Synthetic Endocrine Disruptors in Fragranced Products

Abstract

Endocrine disruptors are molecules that can interfere with the proper functioning of the endocrine system and lead to harmful effects in living organisms. This review focuses on the impact of synthetic fragrances, which are commonly found in personal care and household products, on the endocrine system. The article discusses the different types of hormones in the body and how they interact with receptors to produce signals. It also explores how endocrine disruptors can interfere with hormone signaling and transport, leading to adverse effects in the body. This work underscores the crucial need for further research into the impact of synthetic fragrances on the endocrine system and the importance of using safer alternatives in personal care and household products.

1. Introduction

The endocrine system is the body’s signaling and messenger pathway [1]. Numerous glands in the body produce specialized chemicals called hormones [1,2,3,4,5]. Hormones attach themselves to special proteins inside and outside cells called nuclear receptors and membrane receptors, respectively [4]. Each receptor has a specific site on the protein called a binding site, a spot on the receptor that fits a particular hormone [5]. A binding site on a hormone receptor consists of several functional groups that will weakly bind to the different parts of a hormone and hold it in place [6,7]. The binding sites of hormone receptors are very selective for each type of hormone to prevent accidental activation [4]. The high selectivity of receptor sites means hormones are present in very low concentrations in the body [1]. Once a hormone binds to a receptor, the receptor will activate and generate a signal. An activated hormone receptor will change its physical shape from an “inactive” state to an “active” state. This “active” state creates a signal, which then reacts with other parts of the cell to create a response (Figure 1 and Figure 2) [2,3,4,5].

There are three main types of hormones: eicosanoids, steroids, and peptide derivatives (Figure 3). An eicosanoid hormone is derived from a long-chain fatty acid such as arachidonic acid [8]. They are usually used to signal either the same cell that produced the hormone or another nearby cell and can produce numerous effects in the body depending on the receptor the eicosanoid binds to [8]. The chemical structure of eicosanoids indicates that they can only bind to membrane receptors as they cannot easily cross the cell membrane [8]. A steroid is a hormone derived from the base structure of cholesterol [2,5]. Steroid hormones are used as signaling molecules for male/female sexual expression and stress responses [2,5]. Most steroid hormones are lipophilic, which means they can cross cell membranes to interact with receptors inside cells [2,4]. Peptide-derivative hormones are either made of a single amino acid or a long chain of amino acids (a peptide) [5]. These hormones are created inside cells through the same DNA transcription method as longer proteins [2]. Most are stored inside vesicles, which are small bubbles within cells used for storage and transport and are often ejected out of the cell to interact with other cell types [2]. They will usually signal on surface receptors, as they cannot cross the cell membrane without special transport proteins or storage within vesicles prior to removal [2,4].

2. Endocrine Disruptors

Every day, humans come into contact with both natural and synthetic substances. Some of these exogenous substances can potentially interfere with the hormonal system, leading to their classification as endocrine-disrupting chemicals (EDCs) [4]. An EDC is any molecule that interferes with the endocrine system’s functioning to create a harmful or adverse effect in the body of an organism or its descendants [1,4]. The molecules can be man-made or come from natural sources [9]. Hormone receptors are very selective regarding what can bind to the active site and usually can only be activated by a specific hormone [4]. An EDC can bind to a receptor site accidentally by possessing either a similar carbon structure to a hormone or by possessing similar functional groups in a similar layout to a real hormone [7,10,11,12,13]. The binding affinity is often much lower for a non-hormone molecule but is still possible with a high enough dose and the correct binding orientation [6,10,14]. A few cases exist where an EDC may bind to a receptor despite having no chemical similarity with a hormone. This can be caused by the endocrine disruptor binding in a completely different way than the hormone [6,12].

Both hormones and EDCs can exhibit a nonlinear binding effect [4]. This means that the amount of the substance present in the body does not increase the effect on the endocrine system in a linear pattern [1]. Hormones have such high specificity for their target receptor that a small amount is all that is required for activation. [4]. Trace amounts of an EDC may create a much larger biological response than is expected through the same mechanism [15].

An EDC can affect the endocrine system in several ways, including interfering with or enhancing hormone creation and removal, interfering with hormone signaling, either by binding to a receptor and activating it or blocking access to the receptor site, interfering with the signaling pathway of the hormone after it has activated a receptor, or interfering with or overexpressing transport proteins that move hormones in the body.

Interference or enhancement of hormone creation and removal. Several classes of EDCs can interfere with either the creation or release of hormones from several glands in the body [3,9,16,17]. They can also accelerate the removal of free hormones, causing a loss of hormone activity in the body. There is also a possibility of interfering with the removal process, causing a higher than required number of hormones [9,14].

Interference with hormone signaling, either by binding to a receptor and activating it or blocking access to the receptor site. Hormone receptors are very selective about which hormones bind to them but can be fooled by synthetic molecules with a similar structure [7,9]. If an EDC possesses a similar structure, it can activate the receptor like a hormone and trigger undesired responses (Figure 4) [6,16,17]. When an EDC activates a receptor, it is referred to as an agonist for that receptor type [9]. An endocrine disruptor can also bind to keep the receptor locked into an inactive state, preventing it from being activated at all. This leads to a decrease in the desired signal in the cell and is considered an antagonistic response [9,10,17].

Interference with the hormone’s signaling pathway after it has activated a receptor. This can include activating other molecular binding sites without a hormone signal, interference with secondary messenger molecules at binding sites, activation or interference with enzymes and transcription proteins, and triggering cell signal cascades without a hormone signal [9,13].

Interference with or overexpression of transport proteins that move hormones in the body. Several types of hormones cannot pass through the cellular membrane independently and require special transport proteins. An EDC can block access to the transport proteins, keeping hormones inside or outside of the target cell [16,17]. They can also cause cells to overproduce transport proteins and cause hormones to move too freely.

Health Effects of Endocrine Disruption

Endocrine disruption has been linked to several health concerns, including loss of fertility, reproductive health concerns, various forms of cancer, birth defects/mutations, premature/delayed puberty, obesity/diabetes, hyper and hypothyroidism, immune system interference, and mental health disorders [1,4,14,18,19,20]. The effects of EDCs can extend to other systems of the body, including the nervous (neurotransmitter interference, blood–brain barrier dysfunction, neurodegenerative disease) and cardiovascular systems (hypertension, arrhythmia, atherosclerosis) [21,22].

3. Endocrine Disrupting Chemicals in Fragranced Products

The chemical structures of endocrine-disrupting compounds in fragranced products are shown in Figure 5.

3.1. Phthalates

A phthalate is an ester of phthalic acid, with various varieties named after the carbon chain length attached to the base molecule (Figure 5A) [7,14,23]. Several examples are dimethylphthalate (DMP), diethylphthalate (DEP), dibutylphthalate (DBP), and di-(2-ethylhexyl)phthalate (DEHP) [24]. Small-chain phthalates can be aerosolized; longer varieties will usually stay in solution [18]. They are used as fixatives and solvents in perfumes, and as components of the plastic bottles in which many types of personal care products are stored [7,24,25,26]. The phthalate molecules are not directly bound to the plastic polymers, allowing them to transfer to other liquids or solids that contact the plastic [1,24,27]. Even if phthalates are not part of a particular product’s formula, they may still be found in products due to the phthalate dissolving into the product from the bottle itself [14,18,26,28]. Phthalates have been found to interfere with both thyroid and androgen receptors, along with being suspected of causing several types of cancer and birth defects [1,14,17,20,22,23,29,30,31].

3.2. Parabens

A paraben is an ester of hydroxybenzoic acid (Figure 5B) [14,23]. Several examples include ethylparaben, propylparaben, and butylparaben [31,32]. Due to their antimicrobial properties, they are used as preservatives in many cosmetics, lotions, and makeup formulations [1,26,32]. Parabens are odorless, colorless, heat- and pH-stable, and resistant to chemical reactions [26,31,32]. Though they are generally classified as “safe”, shorter-chain parabens can be absorbed into the skin intact and pass into the bloodstream [18,31]. Long-chain parabens are more concerning due to a higher chance of binding to estrogen and androgen receptors [14,18,26]. There is evidence that parabens can act as artificial estrogens and mild androgen/thyroid blockers and are also suspected of increasing breast cancer risk [3,14,18,31,32]. There is also evidence that parabens cause allergic skin reactions and contact dermatitis in some cases [23,32].

3.3. Alkylphenols

An alkylphenol is a phenol ring combined with a hydrocarbon chain (Figure 5C) [33]. The chain can be straight or branched, with multiple isomers present within a product [24]. Alkylphenols are usually found as ethoxylates (ethylene oxide polymers) in a product but will break down into the base alkylphenol when in the body or natural environment [31]. The ethoxylate form is relatively unstable, but the basic alkylphenol form has shown greater stability and bioaccumulative properties [33]. Alkylphenol ethoxylates are used as surfactants (foaming agents) and cleansers in products like soaps, shampoos, conditioners, and toothpaste [3,18,31,33]. Alkylphenols with longer chains, such as nonylphenol and octophenol, have estrogenic activity and possible antiandrogenic effects [3,18,24,31,33].

3.4. Nitro Musks and Polycyclic Musks

Synthetic musk compounds are used as a substitute for natural musk compounds extracted from animal glands [29,34,35,36]. Natural musk is currently very expensive due to strict regulations on harvesting, so synthetic musks are used in most products to reduce production costs and increase profit [35,37]. Most animal musk compounds are macrocyclic ketones, meaning they are a single large carbon ring containing double-bonded oxygen [35,36]. Nitro musks are benzene rings that contain multiple nitro (NO₂) groups (Figure 5D) [34,36,37]. Several common examples are musk xylene, musk ketone, and musk moskene [36,38]. Polycyclic musks are several linked rings, usually with an oxygen molecule as part of one ring (Figure 5E) [34,37,38]. Several examples are tonalide (AHTN), galaxolide (HHCB), and phantolide (AHMI) [35]. These compounds are found in many perfumes and scented products and are added as a base note to enhance the smell of other components [34,37,38]. Synthetic musks have been found to be endocrine disruptors for all types of hormones, and several are identified as possible carcinogens and organic pollutants [29,31,35,39]. Nitro musks have been found to have a much stronger effect, and several varieties have already been banned or restricted in several countries [18,31,34,36,37].

3.5. UV Filters

A UV filter is a chemical that either absorbs or reflects UV light and is found in sunscreens and in some varieties of cosmetics, such as lip balms, make-up, and lotions [14,17,39,40]. They can either be organic, usually a derivative of benzophenone or cinnamate, or inorganic, like titanium dioxide [14,17,18,31]. Organic filters have chemical structures that absorb the UV region, protecting the skin underneath (Figure 5F) [14,31,40,41]. Inorganic filters block and scatter the incoming light, reducing its impact (Figure 5G) [31,40]. Inorganic UV filters are suspected of endocrine disruption, but organic filters have shown stronger endocrine-disrupting effects on estrogen receptors (ER), androgen receptors (AR), and thyroid receptors (TR) [14,18,31,39,41]. Benzophenones and camphor derivatives have shown concerningly high levels of receptor binding and skin penetration [1,17,18,31,39,40]. Octyl methoxycinnamate, another organic blocker, has also been shown to form highly toxic photoproducts that cause even more harmful effects than the parent molecule [42]. If left in contact with the skin for long enough, organic filters have been shown to be able to cross the skin barrier due to their lipophilic structures [31,41,42]. Inorganic filters have a much harder time crossing the skin barrier, except in cases where nanoparticles are used [31].

3.6. Triclosan

Triclosan is an antibacterial agent used in many cleaning products, such as soaps, shampoos, toothpaste, and hospital disinfectants [18,26,43,44]. It is a weak endocrine disruptor with various effects on ER, AR, and TR [1,18,43]. Due to its presence in many types of oral and skin care products, it tends to enter the body through accidental ingestion and dermal absorption [26,31,44]. Triclosan and its metabolites can enter the environment through wastewater treatment [26,44]. It shares a similar structure with several other categories of molecules, including PCBs (polychlorinated biphenyls) and PCDDs (polychlorinated dibenzodioxins), which are known carcinogens and highly bioaccumulative (Figure 5H) [44]. Triclosan is possibly metabolized into several forms of dioxin under UV radiation while in water [26,44]. On its own, triclosan has not shown definitive carcinogenic properties, but testing has been limited to animal studies [44].

3.7. Cyclic Methylsiloxanes

A siloxane is a silicon-based molecule bonded to oxygen and carbon (Figure 5I) [31,43,45]. Cyclic siloxanes are used as conditioners, smoothing agents, and viscosity-controlling agents in various hair products, lotions, and skin care products [31,43,45,46]. Dermal absorption is usually low, but cyclic siloxanes can be easily volatilized and inhaled [45,46,47]. Evidence shows that cyclic siloxanes can activate ER and possibly block AR. However, the results are inconclusive due to minimal testing [18,31,43]. Smaller rings, such as D4, show a stronger binding effect, but larger rings have a higher chance of bioaccumulation [45,47].

4. Exposure Pathways of Endocrine Disruptors

4.1. Inhalation

This is the most common exposure pathway for small molecules that can evaporate into the air. Other EDCs may be inhaled through dust and powder residues left behind after product use [1,23,28,43,48]. Some small molecules are also slowly released from construction materials like plywood, drywall, linoleum tiles, industrial epoxy, and paints [1,46,48,49]. It also allows for direct access to the bloodstream without barriers for compounds that could be blocked by the skin. Exposure can occur by either direct application of a scented product to the body (such as perfume) or by residual inhalation of molecules absorbed into surfaces or furniture (from an air freshener or cleaning product) [23,38,45,46,49]. While inhalation is the most direct exposure pathway, the amounts of molecules that enter the body this way are in trace amounts compared to other exposure pathways [49,50]. In addition, smaller molecules are easily metabolized and have a lower affinity for binding to receptor sites [18,26].

4.2. Dermal Application

Larger molecules (UV filters, long-chain parabens, etc.) cannot enter the air but can be absorbed through the skin when products containing them are applied. Many types of EDCs are lipophilic, which means they can bypass the skin’s moisture barrier and enter the body [38,41,51]. This absorption occurs more often with products that are made to be left on the skin, such as lotions, some perfumes, and sunscreens [26,34,37,39,41,45,51]. The body can metabolize many types of molecules as they diffuse across the skin barrier, but some of the intact molecules will get through in their pure form [25,30,31,38]. This absorption can be accelerated by additional ingredients found in products like lotions that aid skin penetration and hydration [26,38]. The skin barrier usually prevents water and other polar molecules from entering or exiting, but certain active ingredients in personal care products aid in the diffusion of polar molecules across the barrier. Longer and larger molecules can have a higher endocrine-disrupting effect due to more closely resembling hormones [7,15,18]. They are also harder for the body to metabolize effectively and can accumulate more readily [26].

4.3. Ingestion

Ingestion of EDCs is usually unintentional but can still occur due to trace amounts of personal care products or perfumes settling on food or drinks after use [48,49]. Other EDCs can enter food from packaging or drink containers containing plasticizers like phthalates [7,23,28]. Triclosan can enter the body through products like mouthwash and toothpaste [44]. Many EDCs can also be found in food and water due to human pollution [1,44,52]. These environmental pollutants are highly resistant to removal and will remain in water, plants, and animals until they end up being ingested by humans [52].

5. Environmental Impact

Many types of EDCs in personal care products are highly resistant to removal from the environment and do not easily break down over time. Some compounds can even react to form even more dangerous molecules or highly stable analogs after introduction to the environment [44,53]. These chemicals enter the environment through sewage treatment and waste disposal when products are rinsed off or thrown away [33,37,54,55,56,57,58]. Other products can enter the environment from human waste as metabolites or the parent compound, depending on their reactivity [30,59,60]. Even with processes in place, such as wastewater treatment plants, many EDCs can get released into natural water sources at a substantial rate [33,52,53,54,56,58,59]. The discharge is significantly higher in treatment plants connected to industrial processors or companies that produce personal care products [33,44,55,59,61]. Sediment can act as a storage medium for endocrine disruptors, slowly releasing them back into the water over long periods of time [56,61,62]. Certain organisms, such as earthworms, may also be able to pull EDCs out of soil [62].

EDCs are hazardous to humans and can also affect animals that drink contaminated water or eat contaminated plants, leading to biomagnification and damage to the ecosystem [4,18,57,59]. Their effects on animals can lead to fertility loss, species depopulation, and a higher chance of non-viable offspring [59,62,63]. Evidence shows that EDCs persist in the environment and reach areas with little to no human contact through water systems and ocean currents [52,64].

These environmental effects are not limited to EDCs from personal care products. Additional contaminants such as polyhalogenated compounds (PCBs, brominated flame retardants, polyfluoroalkyls), pesticides, bisphenols (BPA), and others are also accumulative in the environment and act as EDCs [1,3,24,59]. These other categories of endocrine disruptors have shown far more hazardous health effects and can be even harder to remove from the environment due to forming highly stable metabolites [24,65]. Many of these types of EDCs have been restricted or banned in many parts of the world but continue to be present due to their highly persistent nature [3,24].

6. Bioaccumulation and Biomagnification

Bioaccumulation occurs when certain molecules cannot be removed easily from the body and slowly build up to a high concentration [62]. This is mainly caused by repeated exposure to chemicals from various sources (Figure 6) [27,28,43,66]. Hydrophobic molecules tend to bioaccumulate more easily by being absorbed into fat deposits inside organisms [27,56,66]. The human body will attempt to metabolize and remove small amounts of EDCs, but when the number and amount of chemicals from external sources entering the body are too high, the body can no longer remove them effectively [26,28]. Bioaccumulation can easily lead to health concerns, as accumulating molecules can exceed recommended use levels in individuals exposed to multiple sources of the same molecule [1,26,28]. Bioaccumulation also occurs in animals and plants in environments exposed to EDCs [56,57,59,63,66].

Biomagnification occurs when the level of a chemical, such as an EDC, increases with each step up the food chain [62,64,65]. In a contaminated ecosystem, all organisms will have some acquired concentration of the EDC [56,57,61,65]. The amounts acquired are initially small, but with each step up in trophic level, they accumulate more and more from the previous food source (Figure 7) [44,56,61]. Exposure to EDCs starts in the water and soil, accumulating in producers, such as plankton, bacteria, or small plants, and continues to increase as animals consume organisms with higher concentrations [57,65]. Humans are at the top of most food chains and thus receive the highest doses of environmental EDCs [26].

7. Synergistic Effects

Mixtures of EDCs can exert synergistic effects with one another, causing ever stronger effects. A synergistic effect is when a mixture of two or more molecules produces a greater biological effect than a single molecule produces on its own [15,16,18,67]. Some mixtures can possess unpredictable synergy (1 + 1 = 8), where each component magnifies the effect of each other several times higher than what a simple additive effect (1 + 1 = 2) would be expected to produce [1,12,18,68]. The intensity of the synergistic effect is often difficult to predict due to the large number of binding sites in the body, combined with all the possible EDCs that could synergize with each other [15,16,68].

While the exact mechanism of action for mixtures is not well known, synergistic effects are mainly believed to occur due to several molecules simultaneously binding to a hormone receptor [1,12,68]. Hormone receptor binding sites have multiple sites where functional groups on the hormone bind, ensuring the binding site’s selectivity. It is very unlikely that an EDC matches a hormone’s structure and will only match a few functional groups. Two or more smaller endocrine disruptors together could make a near-perfect match to certain receptors if they match the functional groups, even if the main structure does not match [12,68].

It is also possible that a mixture of two EDCs may have synergy with one molecule, which indirectly assists the binding of the other [18]. Some receptors can have additional binding sites that other small molecules can bind to. These small sites affect the shape of the hormone-binding site and can allow for easier binding and activation [69]. This is referred to as allosteric binding.

A synergistic reaction may not even be caused by a mixture of two endocrine disruptors. Environmental pollutants, heavy metals, medications, cleaning agents, and other unrelated chemicals could cause unintentional synergistic effects [1,12,16,67]. Anything that matches part of a binding site functional group may bind when combined with another molecule.

8. Natural vs. Synthetic Products

Most essential oils (EOs) are considered non-harmful under the instructions for recommended use. Authentic EOs are free from synthetic additives and contain only molecules present in the plant [70]. Even in the case of diluted oils, the dilution is usually carried out using carrier oils, which are also plant based and have been shown to be safe in recommended amounts. It is crucial to mention that the chemical profiles and component concentrations of most of the common EOs are well documented in the literature [70]. This makes it much easier for consumers to avoid skin contact with oils containing known skin irritants [70].

On the other hand, perfumes often contain synthetic scent molecules, along with fixatives, preservatives, and other chemicals [25,26,30,71]. They are usually diluted in chemical solvents; some can be hazardous in large doses. They contain EDCs, skin allergens, artificial dyes, and other less desirable chemicals [25,26,29,30,38,72]. Most perfumes will not disclose fragrance ingredients, only ingredients required by law [26,29,37,43,54,71,73]. Required ingredients include synthetic scent molecules known to be hazardous in high doses or known to cause contact allergies [51,54,71,72]. Even when potentially hazardous ingredients are disclosed, they are often used at the maximum allowed concentration or misleadingly labeled [26,43,74]. Perfumes also tend to cause much higher rates of allergic reactions, phototoxicity, skin sensitivity, and other undesirable effects [26,29,30,71]. These problems also extend to many other personal care products [43,73].

An important thing to note is that buying from a reputable source is important for both forms of product. EOs and perfumes can very easily be counterfeited to sell at a discount [70,75,76]. Unlike actual oils or perfumes, these counterfeit products have zero regulation on what goes into them and often have low-quality control and safety standards [76]. Counterfeit perfumes have been found to contain toxic solvents, banned fragrance ingredients, and dangerous levels of ingredients that are restricted in genuine perfume [75].

Some EOs contain certain molecules that have shown signs of endocrine disruption. Anethole from fennel, linalool from lavender, terpinen-4-ol from tea tree oil, and geraniol/nerol from citronella and other flowers are some of the most common examples [31,77,78,79]. While the endocrine-disrupting effects of these molecules have been documented, a very high dose over an extended period of time is required to cause any noticeable effect. Experiments performed on isolated EO components show that the binding affinity for hormone receptors is so low that it can require doses over 10,000 times higher than an artificial hormone to trigger a similar response [77]. If all safety instructions on essential oil bottles are followed, the risk of endocrine disorders from EOs will be minimal. It is important to note that the low reactivity of essential oil components applies to pure oil [80]. Personal care products and perfumes that use essential oil for fragrance may still contain other EDCs, such as parabens, phthalates, and xenoestrogens from soy products used in soaps and lotions [12,78,79]. This can trigger a synergistic effect and produce stronger disruptive effects, either from synthetic components synergizing or the natural ones combined with synthetics [4,78,79].

8.1. Chirality

Several components of EOs are “-chiral-”, which means two molecules with identical formulas and structures that are mirror images of each other but cannot be superimposed on each other [81]. Most chiral molecules have a chiral center, a single carbon atom bonded to four unique atoms or carbon structures. Molecules may also be considered chiral if they contain an unmoving bond, such as a double bond, connected to four unique atoms or carbon structures. A chiral molecule will have two forms, or enantiomers, each with its own physical and chemical properties (Figure 8) [70,81,82]. The two enantiomers will be labeled either (+) or (-), which is determined by the optical properties of the molecule. Chiral molecules will rotate light passing through them, and the direction of the spin will determine which symbol identifies it [81]. Clockwise is +, and counterclockwise is -. Chiral enantiomers may also be labeled with an S or an R, which is related to the absolute configuration of the chiral center.

Natural EOs will usually contain mostly one form of a chiral molecule, but synthetic scents will have an equal mix of the two. Plants tend to have a biological preference for one form of chiral molecule [70,81]. This is because chemical synthesis within plants is based on the chiral structure of both the plant’s DNA and proteins. Both types of large molecules are made of chiral isomers and will create other molecules that match their enantiomer form [81]. Industrial synthesis, however, does not have a biological preference and will result in an equal mix of the two enantiomers. Creating only one enantiomer of a chiral molecule is possible, but it requires many additional steps, making the final product far more expensive.

Chiral molecules will have different biological activities based on their form and can trigger stronger endocrine-disrupting effects [81,82]. Human proteins are chiral, just like plant proteins, and will more easily bind to molecules with the same chiral form. This increases the chance of binding and triggering a biological effect [81]. This is why some EOs show stronger signs of endocrine disruption than others [78]. Artificial scents, conversely, are more likely to trigger an endocrine effect due to having both forms equally present [78].

8.2. “-Green-” or “-All Natural-” Products

Several varieties of personal care products and perfumes may be labeled as “-green-” or “-all-natural-”; however, there is no legal regulation on what the term means [26,43,46]. Regulations are only in place to ensure safety guidelines are followed and known hazardous ingredients are disclosed and kept below limits, but even those guidelines may be ignored [26,29,54,71,74]. Other terms are used for marketing and have no regulatory backing. All natural products can often contain the exact same types of molecules as regular products of the same type in smaller or equal amounts [43,73].

Perfumes might claim to be using scents from natural sources but use synthetically created molecules that are identical to what is found in a plant to replicate the smell [26,70]. Without extensive testing, such as radiocarbon dating, it is difficult to determine if a scent molecule came from a natural or artificial source, as the structure is identical. While there is no real chemical difference between an artificial scent molecule and a natural one with the same structure, the ratios of molecules in a natural essential oil may differ, leading to different effects on the body [70].

A perfume made with only EOs may still contain up to 90% solvent and additives or fixatives [54,70,71]. Different perfume and cologne varieties will use different solvent ratios based on their intended use [54,70]. Solvents such as ethanol can be toxic, aid in hazardous substances diffusing across the skin membrane, or cause allergic skin reactions after extended use [38].

Other products, such as cleaners and personal care products, may also be called “unscented”. However, this can occasionally be untrue due to the presence of “masking scents” [71,74]. Masking scents are molecules added to a product to cover up the smell of cleaning agents or other undesirable smells to create a neutral result [26]. These masking smells are often synthetic oil components like limonene and various forms of pinene [74].

9. Conclusions

In conclusion, the endocrine system plays a crucial role in our body’s overall functioning, and any disruption caused to this system can have severe consequences. Both natural and synthetic substances can act as EDCs, interfering with hormone signaling and affecting the body’s overall health. Chemicals such as phthalates and synthetic musks show many different effects on human health, and their occurrence across so many types of products makes exposure to them quite common. The health effects of EDCs extend far beyond just humans, affecting the water, plants, and animals around us. It is necessary to be aware of the potential dangers of these substances and take the necessary measures to avoid exposure to them and reduce their environmental impact. Researchers must continue studying endocrine disruptors’ impact on human health to identify and mitigate potential risks. Ultimately, our understanding of EDCs can help us make informed decisions and lead healthier lives.