Microplastics (MPs) in Cosmetics: A Review on Their Presence in Personal-Care, Cosmetic, and Cleaning Products (PCCPs) and Sustainable Alternatives from Biobased and Biodegradable Polymers

Abstract

Since the emergence of microplastics, the scientific community has been extremely alarmed regarding their potential risks for and threats to both the environment and human lives. MPs are traced in freshwater and marine environments, day-to-day-life ecosystems, and the bodies of animals and humans. Due to their usage advancements, MPs have become directly or indirectly an integral part of personal care, cosmetics, and cleaning products and appeared as a domestic cause of environmental pollution. Over the years, researchers have ascertained the harmful effects of MPs on the environment. In this regard, the monitoring and assessment of MPs in PCCPs necessitates considerable attention. The worldwide ban legislation on plastic μBs used in cosmetic products has driven researchers to investigate sustainable and eco-friendly alternatives. This review paper summarizes the potential threats of MPs used in cosmetics and the utilization of potential alternatives.

1. Introduction

Plastics have been produced and used since the 1950s, due to their excellent performance. Their low-cost, combined with their unique features, such as durability, usability, and flexibility, made them one of the most popular modern materials to such an extent that researchers note that we are living in the “plastic era” [1,2,3]. However, the worldwide spreading of plastic products has generated vast amounts of plastic wastes that have undeniably aggravated environmental pollution. Once disposed of in the environment, plastic wastes will continuously degrade into small pieces and particles [4].

Since the concept of “microplastics” emerged in 2004, these tiny plastic particles have been discovered in various environmental ecosystems and organisms worldwide. Although there is nouniversally accepted definition of MPs, most researchers and government agencies agree that they comprise solid plastic particles or fibers ranging in size from 5 mm to 100 nanometers [5,6]. In 2019, the European Chemicals Agency (ECHA) proposed a definition for MP: “...a material consisting of solid polymer-containing particles, to which additives or other substances may have been added, and where ≥1% w/w of particles have (i) all dimensions 1 nm ≤ x ≤ 5 mm (ii) for fibers, a length of 3 nm ≤ x ≤ 15 mm and length to diameter ratio of >3 mm” [7].

MPs primarily originate from the fragmentation of larger plastic items, caused by factors such as oxidation, heat, and radiation [8]. However, intentionally produced small plastics have been used in products like abrasives, cleansers, skin exfoliators, fertilizers, or encapsulators since the 1950s, contributing to environmental contamination. The cosmetics industry used to utilize plastics in a wide range of rinse-off formulations. The plastic materials in question are synthetic, non-degradable, water-insoluble materials made up of polymers which, after usage, are anticipated to endure in aquatic environments for centuries.

Lately, the scientific community has focused on intentionally adding solid MPs in the rinse-off cosmetic products, destined for cleansing or exfoliation purposes. These MPs, known as “microbeads” (μBs), have been detected in diverse aquatic environments. Despite their rather undersized contribution to MP pollution, they have received high attention from scientists and environmental agencies, pushing cosmetic manufacturers to phase them out and governments to compel bans [9]. No other form of MPs has faced as many restrictions and prohibitions as those currently being regulated in cosmetic products [10].

The efforts of the cosmetics industry have now focused on the identification of sustainable alternatives to non-degradable polymers that are comparable to exfoliating MPs in terms of performance [11]. Three types of biodegradable materials have been proposed as possible substitutes for cosmetics: (a) natural hard materials (e.g., walnut shells), (b) natural polymers (e.g., cellulose and alginate), and (c) biobased and biodegradable synthetic polymers (e.g., poly(lactic acid) (PLA) and polycaprolactone (PCL)). Hence, in this context, the current paper intends to provide a complete review of the current situation of MPs’ environmental pollution; measures against μB contamination on a worldwide scale, along with their potential limitations; and sustainable biodegradable alternatives for the complete elimination of MPs’ existence in cosmetics industry.

2. MPs in Cosmetic Products

Cosmetic formulations are applied for the treatment of external surfaces of the human body to perform four main functions: (i) preserve good condition, (ii) modify appearance, (iii) provide protection against external factors, and (iv) correct body odor. A more suitable classification includes (i) personal cleansing products (shampoos, deodorants, soaps, etc.); (ii) skin and hair care products (topical treatments, etc.); (iii) beautifying products (lip colors, perfumes, etc.); (iv) protective products (sunscreen, anti-wrinkle treatments, etc.); (v) corrective products (hair dyes, face masks, etc.); (vi) maintenance products (moisturizers, shaving creams, etc.); and (vii) products with active agents (antiseptics, fluoride toothpaste, etc.) [12].

The global cosmetics market reached USD 500 billion in 2017 and is projected to surpass USD 800 billion by 2024, with an annual growth rate of approximately 7% [13]. As baby boomers age, the demand to look younger and more attractive has generated significant market needs and opportunities, making it a global priority. The cosmetics industry has emerged as one of the fastest-growing sectors over the past decade.

In this context, there has been increasing concern about the presence of plastic ingredients in personal-care and cosmetic products (PCCPs) as a potential source of environmental plastic pollution, with MPs being commonly used in PCCPs until they were identified as pollutants. The geometric means of the abundance and mass of MPs found in PCCPs are estimated at 2162 particles per gram and 0.04 g per gram, respectively [14].

The cosmetic and personal-care industry incorporates plastic ingredients into a wide variety of products. These plastics are synthetic, non-degradable, water-insoluble solid materials composed of polymers, combined with additives, to achieve specific properties and functions. The plastic particles used in cosmetics are very small, typically not larger than a millimeter and often as tiny as a few tens of nanometers, making many of them invisible to the naked eye. These particles can be spherical or irregular in shape. The types of plastics used in cosmetics include thermosets, thermoplastics, and silicones. Within these categories, a diverse range of polymers and copolymers are utilized in cosmetic formulations. The roles of these materials in products include film formation, viscosity regulation, skin conditioning, emulsion stabilization, and various other functions [15].

MPs are intentionally added to both rinse-off and leave-on cosmetics. Rinse-off cosmetics are washed down the drain after use, while leave-on cosmetics remain for some time on the body before being washed off or removed with a tissue, wipe, or cotton pad, which usually end up as waste. Examples of rinse-off cosmetics containing MPs include hair- and body-bleaching products, hair-coloring and -nourishing products, shampoos, shower gels, and soaps. Leave-on cosmetics with MPs may include skin care (such as body lotions), makeup (foundations, powders, concealers, mascaras, eye shadows, eye pencils, and eyeliners), lip care, deodorants, sun care, hair-care products (such as leave-on conditioners and dry shampoos), and nail-care products. For instance, a mascara may contain MP fibers, while eye shadow products may contain glitter in the form of MP particles [16].

2.1. Nanoplastics in PCCPs?

Cosmetic formulations containing μBs, such as shampoos and exfoliating scrubs, are mechanically processed and emulsified using high-shear mixers. The degradation of MPs through physical, chemical, and biological processes, includingphoto-oxidation and mechanical abrasion, is likely to result in the formation of nanoplastics (particles smaller than 100 nm), further exacerbating environmental hazards. μBs also experience mechanical stresses during consumer use, and, hence, the potential fragmentation into nanoscale particles should be closely examined [17]. The tiny dimensions of nanoplastics present a unique hazard due to their similarity in size to cell membranes and other cellular constituents. The hydrophobic characteristics of nanoplastics, in conjunction with their small size, may facilitate their penetration into cells through poration or disruption of cell membranes, potentially leading to cytotoxic effects. Investigations utilizing polystyrene (PS) particles on alveolar epithelial cells in laboratory settings have demonstrated that nanoplastic particles are internalized by cells, with the rate of uptake being contingent on particle size (Figure 1) [18].

Despite the increasing concern over the presence of nanoplastics in the environment, there is a lack of information on their successful identification, characterization, and quantification due to significant methodological limitations. A study by Hernandez et al. discovered the unexpected existence of nanoscale particles in commercially available face scrubs, indicating that these particles are intentionally included in the product during manufacturing rather than being a by-product of MPs’ degradation in the environment. The origin of these nanoplastics remains unknown, but it is speculated that they may result from a wide size distribution of the initial material or the breakdown of larger particles during the emulsification process in the production of scrubs [19].This finding is highly alarming since facial scrubs are applied directly on skin, offering a direct route of exposure to the produced nanoplastics.

2.2. Plastic μBs

μBs are solid primary MPs with a diameter of less than 5 mm, intentionally incorporated into cosmetic products for skin cleansing and exfoliation purposes. These μBs are specifically designed within this size range to fulfill various manufacturing functions in PCCPs, such as acting as abrasives. In contrast to MPs that are deliberately prepared at this size range, secondary MPs are derived from the breakdown of larger plastic waste into smaller plastic particles [20]. Initially patented in 1972, μBs saw limited usage until the early 1990s, when cosmetic producers began substituting traditional exfoliating ingredients with them. Their widespread adoption was driven by factors such as durability, cost efficiency, and consistent performance compared to natural alternatives, like inorganic powders, crushed shells, and fruit stones. By the early 2000s, μBs had become so prevalent that it was estimated that nearly every household used a scrub product containing μBs on a daily or weekly basis [21].

Small μBs are utilized in various personal-care products for their abrasive properties. In facial cleansers, smaller μBs are preferred to provide a gentle exfoliation, while larger μBs are incorporated into body scrubs for more intense exfoliation. The size of μBs in facial cleansers and in toothpastes, where a milder cleansing action is required, is typically 2-to-4 times smaller than the size of those in body scrubs. Additionally, μBs can be engineered to exhibit additional beneficial characteristics, such as moisturizing effects, viscosity control, and the ability to prolong product shelf life, by adjusting the composition of the plastic material and additives [22]. Apart from their exfoliating properties, μBs are also commonly used for decorative purposes in cosmetics, such as the spherical, blue-colored μBs found in toothpastes (Figure 2e) [23].

Manufactured to ensure uniformity in size and abrasiveness, plastic μBs (μBs) are deemed safe for use in cosmetics designed for external application due to their minimal evidence of causing dermal irritation, despite the potential risks associated with ingestion. These plastic μBs are also cost-effective. The predominant material used for over 90% of μBs in cosmetic compositions is polyethylene (PE); however, other plastics, like polypropylene (PP), polyethylene terephthalate (PET), polyamide (PA), and polymethyl methacrylate (PMMA), can also be utilized [24].

A primary concern regarding the environmental impact of μBs is their small size, typically less than 0.8 mm and often less than 0.1 mm, making them susceptible to ingestion by various living organisms, particularly at the lower levels of the food chain. Furthermore, μBs, akin to other MPs (MPs), can accumulate in the digestive system, causing harm to the organisms that consume them, and can be transferred to higher trophic levels, thereby progressing through the food chain [23].

2.3. Environmental Exposure and Toxic Effects of MPs from Cosmetics

MPs found in cosmetic products have a prolonged presence in the environment, far surpassing the lifespan of the consumers who use them. Following their release into natural surroundings, MP particles are anticipated to endure for centuries before undergoing full degradation and reintegration into typical biogeochemical processes [25]. The protracted decomposition rates of plastic macromolecules suggest that all plastic ever introduced into the environment remains extant to date. Consequently, any potential negative impacts stemming from the dispersion of MPs into the environment are expected to endure for forthcoming decades and centuries [25]. Still, Akhbarizadeh et al. [26] reported that the processes of tracking and determining the μBs’ abundances from PCCPs in the environment have been challenging.

The colored μBs utilized in beauty products contribute to an aesthetically pleasing appearance, yet upon rinsing, they disperse into water systems, including sewage, land, canals, freshwater streams, and, ultimately, the ocean. Following their use, these μBs are typically disposed of down drains and subsequently reach Wastewater Treatment Plants (WWTPs), where they may escape into natural water sources, without effective means of retrieval. MPs originating from cosmetics are commonly introduced into terrestrial water bodies via residential or industrial wastewater systems. Although WWTPs aim to capture a portion of these MPs in sludge, a significant amount evades river filtration mechanisms and ultimately reaches marine ecosystems, where they float on the ocean’s surface. Estimates suggest that as many as 94,500 μBs could be washed down the drain during a single cleansing event [20].

Numerous research studies have extensively examined the ingestion, buildup, and harmful effects of various MPs in diverse aquatic organisms, such as bivalves, copepods, urchins, dolphins, fishes, and seabirds [27]. The high adsorption capacity of MPs, attributed to their significant specific surface area and strong hydrophobic properties, facilitates the accumulation of persistent organic pollutants (POPs), like alkylphenols, organochlorides, pharmaceuticals, perfluorinated alkyl substances (PFAS), polychlorinated biphenyls (PCBs), polybrominated diethers (PBDs), and polycyclic aromatic hydrocarbons. MPs present a substantial solid surface area, particularly in marine ecosystems, leading to organic contaminants accumulating on their surfaces at levels several orders of magnitude higher than those found in the surrounding water [28], with studies in Japan showing that the number of accumulated PCBs and PBDs on plastic pellets was 105–106 times higher than those in the surrounding seawater [29].

It is well established there are nearly 700 species of aquatic organisms that are affected by MPs, and these MPs can migrate through the food chains, along with the predation of aquatic organisms. MPs aggregate in the digestive tract of organisms, and smaller particles even can enter and stay in the circulatory system. The size affects the accumulation of MPs in the organism, then affecting the growth and reproduction of living organisms. MPs within the size range of plankton are usually ingested by aquatic invertebrates, which are prone to be transferred to vertebrates at the higher end of the food chain [30]. Thus, microplastics easily enter the human food chain, as marine and terrestrial organisms ingest microplastics, and these MPs can affect human health by damaging tissues and possibly bring other toxic chemicals and microorganisms (Figure 3). In vivo studies revealed that treatment of marine fish (Sebastes schlegelii) with PS significantly promoted ROS production. MPs composed of PE, PP, and PVC have been found to cause a comparable intestinal impairment in the zebrafish (Danio rerio) by increasing the glutathione S-transferase (GST) expression. The acute inflammation was stimulated by PP exposure, which leads to the generation of numerous ROS and can then help trigger the degradation, cracking, and additive leaching from the polymer structures [31]. Moreover, microplastics in the human body can cause various adverse health effects, including lethality, mental and reproduction problems, intestinal damage, immune problems, and neurotoxicity [32,33]. Apart from the direct impact of the accumulation of MPs in biota, the research should also focus on the carried organic pollutants.

The ability of MPs to influence the structure and composition of microbial communities is a significant concern regarding their presence in freshwater ecosystems [34]. MPs have the capacity to accumulate nutrients, and, as they can be transported between different environments, they create a stable, enduring, and mobile habitat that supports microbial growth. This novel habitat formed by MPs is referred to as the “plastisphere”. While plastispheres were initially identified in marine ecosystems, they have also been observed in freshwater environments. The formation of plastispheres is influenced by various physicochemical and environmental factors, such as oxygen and nutrient levels, temperature, light exposure, and pressure [35].

To date, there is limited knowledge available on the toxicological impacts, mechanisms, and dynamics of MPs in the human body, despite regular exposure through ingestion, inhalation, and skin contact (Figure 4). MPs deriving from cosmetic products are most likely to be ingested by humans though seafood, drinking water, and table salts. MP dermal exposure usually occurs when cleaning the body with products such as body scrubs and toothpastes. Due to the fact that skin pores range in size from 40 to 80 µm, the dermal barrier could be crossed by fragmented nanoparticles [36]. Numerous works have shown that factors such as the shape, size, and surface functionalization of microparticles are significant aspects regarding their internalization by cells and distribution in different tissues and human organs [37]. Research suggests that individuals may consume between 39 × 10³ to 52 × 10³ MP particles annually through food alone, with additional exposure through inhalation potentially increasing this estimate to 74 × 10³ to 12.1 × 10⁴ particles per year. The small size of these particles plays a significant role in enhancing their bioavailability, with nanoparticles, due to their smaller particle size, showing greater capability to penetrate into the cell membranes [26].

2.4. Glitter: An Overlooked Source of Primary MPs

While the use of MPs in cosmetic products is largely restricted, there exists another significant source of MPs that is comparable to μBs, whose environmental impact has received relatively limited attention [38].These shimmering particles, commonly known as glitters, are frequently incorporated into various cosmetic products, including eye pencils, liquid and powder eyeshadows, highlighters, bronzers, lip glosses, lipsticks, makeup, body paints, facial scrubs, nail polish, and lacquers (Figure 5). At a significantly reduced cost, glitter particles are introduced into the environment either directly or indirectly (such as through discharge into sewage systems during cleaning or washing) upon initial application. Glitter is utilized more extensively in cosmetic formulations compared to μBs; however, it has garnered limited scrutiny from researchers, who focus more on the environmental impact of MPs. This is primarily due to its tendency to settle in sediments, while many studies typically collect samples that are located on the surface [39].

Glitter is commonly employed for decorative purposes due to its highly appealing shiny, small, vibrant, and colorful appearance. A majority of glitter particles are typically composed of metalized PET, possessinga true density of 1.38 g cm⁻³ and a melting point of 260 °C. Additionally, there are commercially accessible variations in glitter made from acrylic, PMMA, poly(vinyl chloride) (PVC) and plastic epoxy resin mixtures, or melamine and phenolic resin mixtures. Notably, glitter exhibits insolubility in water [41]. Upon application, glitter particles begin to sparkle on surfaces such as the body, clothing, and other objects, as well as dispersing throughout the surrounding environment. Through contact, these particles can easily transfer from one surface to another. Studies have identified the presence of glitter particles in sewage sludge samples collected from riverbed sediments in the UK [42,43] and samples from a wastewater plant located in Norway [44]. Moreover, mussels and oysters gathered from mollusk farms located in Southern Brazil contained glitter particles in their soft tissues [45].

While glitter is considered safe for human use within specified levels, there is ongoing debate concerning its potential toxicity towards aquatic organisms. Studies have indicated that, even at low concentrations, glitter can be harmful to zebrafish embryos (Danio rerio) [46]. Furthermore, exposure to glitter has been shown to trigger oxidative stress in adult specimens of the mussel Mytillusgalloprovincialis [47] and brine shrimp Artemia salina [48]. Abessa et al. concluded that, at high concentrations, glitter was responsible for causing adverse effects on the embryonic development of the sea urchin Echinometra lucunter (Figure 6A,B), mussel Perna perna (Figure 6C,D), and urchin Arbacia lixula (Figure 6E); therefore, glitter particles may potentially affect other marine organisms [45].In comparison to μBs, which typically exhibit circular or irregular shapes, glitters are characterized by their thin form and sharp edges. Consequently, the ingestion of glitters by marine organisms may cause more severe problems. Furthermore, glitters have been associated with inducing allergic reactions, itching, and skin wounds in certain individuals. Lastly, they have the potential to cause ocular injuries, such as eye lesions, swelling, inflammation, vision loss, corneal abrasions, and even blindness.

The harmful effects of glitter are mainly attributed to the presence of metals, such as silver (Ag), oxidant compounds, and volatile substances. These components can be found in plastics or generated during the degradation of plastic materials in water environments. An examination of water samples from Brazil revealed that the levels of silver exceeded the permissible limits for marine waters, indicating that glitter particles have the potential to leach metals into the surrounding waters [45]. Many individuals lack awareness regarding the environmental consequences associated with the utilization of glitters. For example, the unregulated application of PET glitters, characterized by their diminutive size, metallized composition, non-biodegradability, and enduring presence in ecosystems, presents substantial risks to environmental integrity and biodiversity. Consequently, it is imperative to impose restrictions on the production and uncontrolled deployment of these components through the implementation of efficacious measures [41]. Renewable botanical resources, including soluble seaweed, regenerated cellulose primarily sourced from Eucalyptus trees, and plant-derived glycerin, are being developed as substitutes for traditional glitters. Biodegradable glitters composed of plant-based components and adorned with mineral pigments exhibit a narrower range of color and shape choices compared to their plastic alternatives. Furthermore, these eco-friendly components are approximately 35% less rigid than plastic glitters [41,49].

2.5. Legislation of MPs in Cosmetics

In 2013, major global personal-care and cosmetic corporations, including L’Oréal, Colgate-Palmolive, Unilever, Johnson & Johnson, Beiersdorf, Procter & Gamble, and Unilever, made a collective pledge to eliminate μBs from their full product lines. Consequently, this initiative led to the comprehensive exclusion of μBs from all rinse-off items certified under the European Union Ecolabel [50]. Prohibiting the use of plastic μBs in rinse-off cosmetics as a strategy to combat marine pollution offers a solution that targets the root cause of the issue with potentially minimal consequences. Such bans are supported by public sentiment and necessitate only limited involvement from policymakers, without causing substantial disruptions to the cosmetics industry [20].

Considering the widespread distribution and potential harm caused by MP pollutants, addressing this issue on a global scale is necessary, as it is not feasible to resolve by simply prohibiting MP-containing products in a few countries. While the μBs found in cosmetics may not be the primary source of MP pollution, they still present environmental risks when released into water bodies and are only partially filtered by Wastewater Treatment Plants. Various environmental organizations have advocated for the elimination of MPs in personal-care and cosmetic products (PCCPs), leading to the implementation or planning of bans in several countries. In January 2019, the European Chemicals Agency (ECHA) proposed restrictions on the intentional inclusion of MP particles in consumer and professional mixtures across the European Union, with the expectation that this measure would reduce the environmental release of MPs by approximately 400,000 tons over a span of 20 years [23]. The first measures, for example, the ban on plastic-based loose glitter and μBs added to cosmetic formulations, entered into force on 17 October 2023 [51,52]. The transitional periods for the implementation of the sales ban of these products in the EU are indicated in

Table 1. Transitional period for the application of the ban (according to paragraph 6 under entry 78 of Annex XVII to R/EC 1907/2006) [52].

Designation of the Substance, of the Group of Substances, or of the Mixture	Date of Application
Rinse-off products (intended to be removed after application), unless they contain beads for exfoliation, polishing, or cleansing	From 17 October 2027
Detergents, waxes, polishes, and air fresheners, unless they contain μBs	From 17 October 2028
Synthetic polymer microparticles for use in the encapsulation of fragrances Leave-on product (intended to stay in prolonged contact with the skin)	From 17 October 2029
Lip products, nail products, and makeup products, unless they contain μBs	From 17 October 2035

.

According to the European Cosmetic Ingredient Database (CosIng), the following polymers are currently employed in cosmetics as abrasives and will be reasonably abolished in Europe [23]: 1,4-butandiol copolymer, ammonium acryloyldimethyltaurate copolymer, ethylene/propylene copolymer, and PE/polylactic acid.

Since 1 January 2020, it has been illegal in Italy to advertise cosmetic rinse-off products that contain MPs and have an exfoliating or detergent function [11].

Apart from the European Union, USA, Canada, and China, New Zealand and South Korea are the only non-European countries, alongside the Taiwan province, that have already banned the use of μBs in rinse-off cosmetics [52].

The United Arab Emirates (UAE) is amongst the nations that have not yet introduced any regulations regarding the presence of MPs in rinse-off cosmetics. Despite this, the UAE is characterized by a substantial expatriate community and is recognized as a diverse cultural hub. It holds the seventh position globally in terms of per capita consumption of cosmetic products. Owing to its diverse population, cosmetics are sourced from various countries worldwide. Additionally, a notable local cosmetic industry has emerged, with international brands also manufacturing cosmetics under licensing agreements in the UAE. A study conducted in 2020 examined 74 randomly selected PCCPs, revealing that 12% of them contained plastic μBs, specifically polyethylene (PE) [53].

In India, the Indian Bureau of Standards (ISB) is responsible for regulating the cosmetics industry. While the regulations mention the use of polyethylene (PE) in cosmetics, there is no specific reference to “solid plastic μBs of size less than 5 mm” in personal-care and cosmetic products. Despite India’s significant position in the global cosmetic market, many products lack complete or clear labeling and ingredient information. Plastic μBs are present in various personal-care and cosmetic products, either on their own or in combination with natural alternatives. A recent study has revealed that 49.12% of products contained irregular or smooth μBs, predominantly made of PE, followed by PP, PS, polyurethane (PU), and polycaprolactone (PCL) (Figure 7). A considerable proportion of products (23.33%) contained cellulose μBs, with uncertainties regarding their biodegradability. The total annual emission of μBs from personal-care products was estimated to be 1.37 × 10¹⁹ (average) in 2021, and it is projected to increase to 1.61 × 10¹⁹ (average) by 2030, a concerning figure compared to studies on personal-care and cosmetic products from other regions. The high emission estimates are attributed to factors such as the large population, rapidly expanding consumer market, and inadequate wastewater treatment efficiency [54].

Currently, existing bans prohibit the sale of PCCPs containing μBs; however, there is ambiguity regarding whether the manufacturing and importation of such products are also restricted. International agreements may also influence national bans, such as the “Trans-Tasman Agreement” between New Zealand and Australia, as it may allow the importation of products with μBs into New Zealand from Australia, even though their sale is banned in New Zealand. Similarly, Canada has banned both the manufacturing and inclusion of μBs in Canadian toiletries, yet it permits their transportation through the country [16]. PCCPS that are currently being sold in the UAE market are imported from countries where enacted restrictions exist, like the US, pointing out that multinational companies may still manufacture and sell cosmetics in markets that have not implemented any bans [55].

3. Natural μBs

In 2020, the beauty and skincare industry had to reinvent itself to quickly adapt to the latest demands of an unpredictable and attentive market [56]. The increased prevalence of social media and internet platforms has heightened public awareness regarding the potential hazards associated with the use of various chemicals in cosmetics, while also emphasizing the health advantages of utilizing natural ingredients sourced from plants and other organic materials. Consequently, both the cosmetic industry and scientific-research sector are directing greater focus towards natural products. One of the primary challenges faced in this context is determining an optimal equilibrium between the concepts of “natural” and the chemical composition of cosmetic products.

Algae-derived phyto-molecules are considered to be viable alternative sources for promoting the sustainable development of μBs, offering a range of biological activities. Polysaccharides are recognized for their significant role as key bioactive components in PCCPs and are therefore being explored as sustainable substitutes in the cosmetics industry [57].

Alginates are a type of salt derived from alginic acid that are categorized as linear, block copolymers consisting of α-L-guluronic acid and β-D-mannuronic acid residues connected by a glycosidic bond. These compounds are primarily sourced from the cell walls of marine algae, particularly brown algae (Phaeophyceae). When combined with divalent cations, alginates have the ability to create a gel-like structure that offers structural integrity and a form similar to that of the μBs [58]. Kozlowska et al. [59] prepared natural microparticles of sodium alginate and sodium alginate with starch as abrasive agents for the exfoliation of dead skin cells. Figure 8 shows that the obtained microparticles had a regular, spherical shape, which minimizes the risk of skin irritation during the application of the exfoliating product. Alginate microparticles were characterized by a smoother surface than that made by the combination of alginate and starch. Skin examination after the application of the peel-off formulations containing the prepared natural μBs showed no irritation or redness, regardless of the type of the microparticles tested or their composition.

Bae et al. [60] produced micronized alginate μBs via solution electrospraying, involving an ion-exchange reaction between sodium alginate and calcium chloride. With an increase in alginate concentration and needle diameter, the size of the alginate μBs proportionally increased due to the mass flow rate of alginate. The swelling capacity of the alginate μBs was found to be 160% in distilled water, while rapid degradation occurred in seawater, owing to the reversible ion-exchange reaction between Ca²⁺ in the μBs and Na⁺ in seawater. These findings suggest that alginate μBs hold promise as environmentally friendly additives in cosmetics.

Similarly, novel seaweed polysaccharide-based encapsulated curcumin-loaded μBs were fabricated by Selvasudha [58] and his team as an alternative to plastic μBs in exfoliating biocosmetic products. Biodegradation studies in marine water revealed approximately 98% weight loss by the end of the 10th day, compared to the 0% weight loss of the commercial synthetic polymer used in cosmetic products. The encapsulation of curcumin provided enhanced antioxidant and antimicrobial properties and exhibited a profound release profile and considerable stability in lipophilic olive oil that is highly significant in exfoliating cosmetics. Furthermore, cell viability assays revealed that the curcumin-loaded μBs exhibited cell viability. In general, natural polysaccharides, such as alginates, are considered to be safe even at high concentrations, in contrast to synthetic polymers like PS, where significant cytotoxicity has been reported in the human-derived HDFs, HMC-1, and PBMCs cells at concentrations up to 500 µg/mL, as well as skin toxicity.

Hence, based on the above, natural and sustainable alternatives to MPs should be promoted. Examples include coffee, apricots, walnuts, kiwi seeds, and soluble cellulose beads, among others. While these alternatives may not possess the same vibrant colors, smooth textures, and visual appeal as plastic μBs, they offer superior environmental benefits, making them more appealing to modern consumers.

4. Biopolymers as Sustainable Alternatives

MP contamination is considered to be permanent due to the inherent non-degradable nature of conventional plastics like PE, PP, and PS. Furthermore, the scattered MPs present in the ocean pose a challenge, as there are currently no effective means of collection [61]. Moreover, these polymers are sourced from non-renewable origins like petroleum hydrocarbons. Therefore, there is a growing demand for biobased materials derived from renewable and environmentally sustainable sources [62]. In recent years, there has been a surge in interest regarding the advancement of biobased and biodegradable polymers as a viable and eco-friendly substitute for conventional materials. This emerging category of substances presents promising solutions to prevalent issues such as the depletion of resources and the proliferation of plastic waste. By developing sustainable bioplastics utilizing biobased or biodegradable polymers, opportunities emerge to effectively tackle these environmental concerns. Bioplastics are crafted from materials sourced from either renewable origins or petroleum-based reservoirs, with a primary emphasis on diminishing carbon emissions, improving recyclability, and advocating for biodegradability. Moreover, the manufacturing of sustainable bioplastics is in alignment with the objectives delineated in the United Nations’ sustainability development goals (UN SDGs) and the European circular-economy strategy [63].

Ju and his group [63], in a very interesting work, using a water-in-oil inverse emulsion system, produced environmentally friendly chitosan-based beads (chito-beads) (Figure 9) with a uniform spherical shape and a diameter of 280 µm. Chito-beads displayed a higher cleansing capability than conventional PE μBs, with a hardness of 128 MPa. Additionally, the obtained results indicated that these chito-beads may be used to remove potentially toxic elements and that they are stable and functional for commercial cleansing applications. In general, chito-beads seem to have the ability to absorb potentially toxic elements (PTEs) and organic pollutants, owing to their acetyl amide groups. Also, these chito-beads were fully degraded by microorganisms, enzymes, and seawater, as well as in soil, without inducing any toxicity, while the degradation products in the case of the soil environment exhibited positive effects on both plant germination and growth.

King et al. [64], working with the precursor of chitosan (i.e., chitin), prepared biodegradable, biocompatible, and porous μBs of low toxicity using the ionic liquid (IL) 1-ethyl-3-methylimidazo-lium acetate ([C₂mim][OAc]). Release studies showed that the porous beads can be employed for the encapsulation and release of active compounds with different chemical structures. Approximately 90% of the model bioactive compounds were successfully released after 7 h, providing a steady and prolonged release. Hence, these materials may also be used as μΒs, since, in many cases, there is a common need to encapsulate dyes and/or anti-inflammatory agents.

Nam et al. [65] prepared biodegradable PLA μBs through the eco-friendly melt-electrospraying method. E-beam pretreatment was used to enhance the melt processability of high-molecular-weight PLA. Furthermore, the PLA μBs showed much lower POPs adsorption than commercial PE and MCC, owing to their smooth and non-porous surface, as well as their low specific surface area. The degradability of PLA MBs was investigated in various aquatic environments, such as tap water, distilled water, seawater, and NaOH solutions, with results showing that the hydrolysis rate of the PLA μBs in NaOH solutions was accelerated (Figure 10).

In a similar work, biodegradable PCL μBs were prepared using the melt-electrospraying methodand compared with PLA, PE, and MCC [65]. The rheological results suggested that the PLA showed irradiation-degradable behavior, while the PCL showed irradiation-crosslinking. The cleansing-efficiency evaluation indicated that the PCL-based μBs presented high skin hydration and a low irritation, similar to PE and MCC μBs. Degradation studies in natural seawater and NaOH solutions (pH 11) revealed that the degradation rate of PCL and PLA μBs was dependent on the alkyl chain length between the ester bonds in alkaline environments: PLA showed faster degradation than PCL. Based on these promising results, aliphatic polyesters such as PCL and PLA can be considered suitable eco-friendly materials to replace non-biodegradable beads in cosmetics and healthcare products.

However, using PLA as an alternative to conventional μBs in cosmetic products inevitably involves evaluating its ecotoxicological threats in a comprehensive manner. Malafaia et al. [67] first tested the potential harmful consequences of exposing amphibian representatives to PLA bioMPs (PLA BioMP). During their research, they exposed Physalaemus cuvieri tadpoles to PLA BioMP at environmentally relevant amounts (760 and 15,020 μg/L) and observed physiological changes in them. Their collected data indicated that the biopolymer uptake altered tadpoles’ growth and development features, decreased their lipid reserves, and increased reactive oxygen-species and nitric oxide-species production after 14-day exposure. Furthermore, the two tested concentrations were responsible for the emergence of a cholinesterase effect, which was marked by elevated acetylcholinesterase and butyrylcholinesterase. These findings were indicative of the presence of a neurotoxic action for the PLA BioMP.

Polyhydroxyalkanoates (PHAs), a class of bacterial polyesters especially biodegradable in marine environment, have also been investigated as alternatives for applications in cosmetics meeting environmental constraints. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) (Figure 11a) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) (Figure 11b) were used to prepare μBs, with diameter ranging from 50 to 100 μm, using the emulsion-evaporation method. This manufacturing process enabled the preparation of spherical PHA μΒs with increased roughness, as compared to amorphous PLA smooth beads. The degradation behavior of these PHA μBs was tested under a marine environment and revealed a rapid degradation process, faster than that of cellulose, and a degradation rate correlated with the crystalline content. Interestingly enough, the prepared PHA microparticles were stable in aquatic mediums commonly used in cosmetic products, while also being rapidly biodegradable in the marine environment [68].

Using a facile and green production process, You et al. [69] also manufactured biodegradable PHBHV μBs for application as skin exfoliators. The PHBHV μBs were rapidly fabricated via a solvent-exchange method in which dimethyl isosorbide (DMI) acted as a green solvent and a polysorbate 80 aqueous solution was employed as the antisolvent. Phytotoxicity studies showed that the PHBHV μBs caused no harmful effects on wheat and lettuce growth, while biocompatibility testing implied that the μBs were biocompatible and eco-friendly. Moreover, degradation experiments revealed that PHBV μBs can degrade in the presence of microorganisms but remain stable without microbes.

μBs made of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB-4HB) were also fabricated using melt-electrospraying and then incorporated into liquid soaps to investigate their cleansing efficacy. The soap with the MB-free cleanser took nearly 180 s to totally remove contaminants from the inner part of the human forearm, whereas the soap with the sample containing P3HB-4HB MB took approximately 70 s (Figure 12). Moreover, the P3HB-4HB μBs were more effective in the contaminant removal than commercial MCC particles and exhibited a similar removal time as commercial PE and Walnut particles. When tested on pig skin for cleansing an inorganic-based sunscreen, P3HB-4HB μBs were able to completely remove the sunscreen, as compared to fresh water. Similarly, the P3HB-4HB μBs showed a significantly lower POP adsorption as compared to commercial μBs, owing to their smooth and regular surface [69].

5. Conclusions

Plastics have a lasting presence in the environment, posing a persistent threat to marine ecosystems over extended periods. MP pollution is subtle and often goes unnoticed, with its ecological consequences frequently overlooked. While the adverse effects of MPs in marine settings have been a primary focus of concern, there are additional environmental implications associated with the sourcing, production, and transportation processes involved in the lifecycle of plastic-containing products, as well as post-consumer use.

μBs, which are commonly used in PCCPs for skin cleansing and exfoliation, are a significant source of MP pollution in marine environments. Following their use, a noteworthy portion of these μBs escapes from Wastewater Treatment Plants (WWTPs) and enters freshwater bodies or oceans. Numerous studies are increasingly emphasizing the detrimental impacts of MPs of various sizes on organisms and the potential risks to human health. Given that μBs are challenging to retrieve from water post-use and that natural alternatives exist at comparable costs, their permanent exclusion from cosmetics is deemed the most favorable option, despite their minimal contribution to the overall presence of MPs in the environment (less than 3%).

Monitoring different sources of plastic pollution, such as surface runoff into water bodies, is a complex task. However, μBs in PCCPs are identified as significant sources of pollution, and their release can be easily prevented. One effective approach is to encourage the voluntary discontinuation of μBs in PCCPs. Currently, there is a growing global movement towards eliminating plastic μBs from cosmetics, driven by an environmental standard that has demonstrated considerable influence on consumer behavior, government regulations, and corporate marketing strategies.

Various natural materials and biodegradable polymers have been studied as eco-friendly options to replace conventional plastics like PE in the production of μBs for self-cleansing applications. These alternatives demonstrate superior mechanical properties and possess key characteristics such as biodegradability, biocompatibility, low adsorption of POPs, and scalability. Aliphatic biodegradable polyesters like PLA, PCL, and PHA are viable options for creating μBs using environmentally friendly methods, offering a sustainable alternative to non-biodegradable beads in cosmetics and healthcare products.

Although it is anticipated that none of the substitute options will result in more severe or equivalent effects in marine pollution, there has been limited examination of their comprehensive environmental efficacy throughout their life cycle. Numerous non-plastic alternatives are currently employed in PCCPs, with additional options in the developmental stage. It is imperative to ensure that these alternatives do not introduce environmental drawbacks that could surpass the advantages derived from the prohibition. However, a thorough evaluation of the broader environmental impacts of these potential replacements over their lifespan has not been conducted, necessitating caution to prevent potential scenarios where the environmental costs of their utilization outweigh the benefits resulting from the bans.