Biologically Active Components and Skincare Benefits of Rice Fermentation Products: A Review

Abstract

With the growing demand for environmental sustainability, the cosmetics industry is increasingly turning to natural ingredients with high bioactivity and efficacy. Rice, a staple food in many cultures, particularly in Asia, is renowned for its nutritional and medicinal benefits, as well as its skincare properties. Numerous studies have emphasized the multifunctional benefits of rice in skincare, ranging from its ability to enhance hydration to its effectiveness in addressing signs of aging, positioning it as a promising ingredient in cosmetic formulations. Recently, fermentation has emerged as an innovative technique that significantly enhances the bioactive potential of rice. This process amplifies the production of beneficial compounds, such as organic acids, amino acids, polyphenols, polysaccharides, vitamins, and minerals. Previous studies have shown that rice fermentation products (RFPs) exhibit a range of skincare benefits, including moisturization, antioxidation, anti-inflammation, whitening, and anti-aging effects. This review provides an overview of the fermentation process and advantages of RFPs, followed by a detailed analysis of their key bioactive components and the diverse skincare benefits they offer. Moreover, we discuss the challenges related to the standardization, component analysis, and efficacy evaluation of these products, and we conclude with potential future research directions to fully explore the skincare potential of RFPs.

1. Introduction

As consumers become increasingly aware of the ecological impact of their beauty choices, there is a discernible shift toward natural, renewable, and eco-friendly alternatives in the cosmetics industry. This growing demand for sustainable solutions is driving the industry to prioritize ingredients with enhanced biological activity and efficacy [1]. Rice, a staple food in many countries, particularly in Asia, has long been valued not only for its culinary significance but also for its extensive nutritional and medicinal properties, making it a key component in both traditional medicine and skincare [2].

Rice, a rich source of amino acids, peptides, organic acids, polyphenols, vitamins, and polysaccharides, has garnered growing attention owing to its diverse skincare benefits [3]. Research has demonstrated its potential to enhance skin hydration, improve skin barrier function, mitigate oxidative stress, promote skin whitening, and address signs of aging [4]. Recent trends indicate a significant rise in scientific interest regarding the skincare applications of rice, demonstrated by the increasing number of related publications in the Google Scholar database (Figure 1). This expanding research underscores the potential of rice as a promising natural ingredient for future exploration, driving innovation in the development of advanced and effective skincare formulations.

In recent years, fermentation has emerged as an innovative process that significantly enhances the bioactive potential of rice, yielding more effective skincare ingredients [5]. During the rice fermentation process, microorganisms such as bacteria, yeast, and fungi break down complex starches into bioactive compounds, including amino acids, peptides, organic acids, and polyphenols [6,7]. This transformation not only increases the content and bioavailability of these compounds but also amplifies their functional properties, making them more suitable for skincare applications [8,9]. Moreover, the fermentation process enhances the biocompatibility and bioavailability of rice, while simultaneously reducing irritation, thereby improving their efficacy in topical skincare applications [10,11].

A growing body of research has demonstrated the significant potential of rice fermentation products (RFPs) in skincare, which is owing to their multifaceted benefits, including moisturizing, skin barrier repair, antioxidant, anti-inflammatory, whitening, and anti-aging effects [12,13]. Previous studies have shown that RFPs can enhance the skin’s barrier function, brighten the complexion, reduce fine lines, and improve elasticity, as evidenced by numerous in vitro, animal, and several human studies [14,15]. Furthermore, the anti-inflammatory properties of RFPs have demonstrated efficacy in managing common skin conditions like acne, eczema, and psoriasis [16]. These benefits are primarily attributed to the synergistic interactions of the bioactive compounds within RFPs, which collectively contribute to improved skin health.

This review aims to provide a comprehensive overview of the biologically active components in RFPs and their skincare benefits. We first discuss the fermentation process and advantages of RFPs, followed by a detailed analysis of their key bioactive components and the diverse skincare benefits they provide. Moreover, we address the challenges related to the formulation and standardization of these products, and we outline potential future research directions to fully explore their capabilities in skincare applications.

2. Rice Fermentation and Its Advantages

Rice generally consists of four main parts: the husk (~20%), the germ (~2%), the endosperm (~70%), and the bran (~8%) (Figure 2). The husk, primarily composed of cellulose, serves as the outer protective layer and is removed during processing. For fermentation purposes, the germ and bran of rice are commonly utilized due to their higher nutrient contents (e.g., proteins, vitamins, amino acids, and polyphenols) and their capacity to support microbial growth. The endosperm, primarily composed of starch, is less frequently utilized in fermentation; however, it can function as a secondary carbon source, as microorganisms are capable of hydrolyzing the starch into fermentable sugars.

2.1. Rice Fermentation Process

Fermentation is a biochemical process in which microorganisms such as bacteria, yeast, and fungi convert complex organic compounds into simpler molecules, including acids, gases, and alcohols [17]. In the context of rice fermentation, this process transforms rice starches into bioactive compounds, thereby enhancing both the nutritional and functional properties of the rice [18]. The rice fermentation process typically involves several critical stages: selecting the raw rice variety, inoculating it with specific microbial strains, controlling fermentation conditions, and subsequently extracting and purifying the bioactive components.

The selection of rice variety, including white, brown, red, black, or glutinous rice, plays a critical role in the fermentation process, nutritional composition, and the efficacy of the final RFP [19]. Brown rice, for example, contains higher levels of vitamins, minerals, and antioxidants than white rice [20]. The fermentation process of brown rice is slower than that of white rice, but it produces a greater variety of organic acids, amino acids, polyphenols, and peptides, which exhibit strong antioxidant, anti-inflammatory, and anti-aging effects. A recent study found that pigmented rice varieties, such as red and black rice, are rich in anthocyanins, which enhance the production of additional antioxidant compounds, including polyphenols, during fermentation. These compounds exhibit potent antioxidant, anti-inflammatory, and anti-aging effects, making them valuable ingredients for skincare [21].

Microorganisms are pivotal in determining the characteristics and benefits of the final RFP. Different microorganisms result in distinct end-products and skincare benefits of RFP. In skincare applications, Lactobacillus (lactic acid bacteria), Saccharomyces cerevisiae (yeast), and Aspergillus species (fungi) are commonly employed to ferment rice. Studies have shown that Lactobacillus strains can produce lactic acid, which significantly lowers the pH of the fermentation process [22,23]. This acidification not only contributes to the production of short-chain fatty acids and other organic acids but also serves as a natural preservative. In contrast, Saccharomyces cerevisiae secretes various enzymes, such as proteases, amylases, and lipases, which facilitate the breakdown of proteins, starches, and fats in rice, leading to the production of amino acids and peptides [24]. Liu et al. investigated the use of lactic acid bacteria and aroma-producing yeasts in rice fermentation and found that the resulting RFPs exhibited significant differences in acid production and antioxidant capacity [25].

In addition to the fermentation strain, the fermentation conditions also influence the fermentation process and the bioavailability of active compounds [26]. Initial rice processing, including milling and soaking, enhances the accessibility of starches and other nutrients in rice, thereby improving fermentation efficiency. Additionally, key fermentation factors such as temperature, pH, and fermentation duration must be carefully controlled to optimize microbial activity and maximize the production of bioactive compounds [27]. Following fermentation, a range of extraction and purification techniques, such as solvent or water extraction, filtration, centrifugation, and chromatography, are employed to isolate and concentrate these bioactive compounds, making them suitable for incorporation into skincare formulations [28].

2.2. Advantages of RFPs

2.2.1. Increased Production of Bioactive Compounds

Fermentation significantly enhances the production of bioactive compounds that are not present in the original raw rice as well as increases the levels of existing components [29]. A recent review highlighted that fermentation substantially increased the bioactive phenolic and peptide contents in rice, resulting in enhanced antioxidant and anti-inflammatory activities [30]. Schmidt et al. demonstrated that the fermentation of rice with the fungus Rhizopus oryzae via solid-state fermentation more than doubled the content of phenolic compounds [31]. Notably, the concentration of phenolic acids increased dramatically, with ferulic acid showing the most substantial rise, increasing from 33 mg/g to 765 mg/g following fermentation. Lim et al. observed that the concentration of γ-aminobutyric acid, a neurotransmitter with significant neuroprotective and antioxidative properties, was increased 16.8-fold in Lactobacillus reuteri-fermented rice compared to raw rice [32].

2.2.2. Enhanced Biocompatibility and Bioavailability

Fermentation increases the biochemical and physiological activity of active ingredients in rice by breaking down high-molecular-weight compounds into smaller, low-molecular-weight substances. This transformation significantly improves their biocompatibility and bioavailability, enabling these compounds to be more effectively utilized by the skin [33]. The fermentation process also facilitates the utilization of active ingredients that might otherwise be too large to efficiently penetrate the skin barrier. For example, the protease generated during fermentation hydrolyzes large proteins into smaller amino acids and peptides, which are more readily absorbed by the skin [34]. Furthermore, a review by Janarny et al. demonstrated that rice fermentation modifies the structural properties of polysaccharides by converting larger molecules into smaller, more absorbable forms, thereby boosting their absorption and efficacy [29].

2.2.3. Improved Skin Tolerance and Reduced Irritation

Fermented rice ingredients are generally milder on the skin compared to their non-fermented counterparts, making them particularly beneficial for individuals with sensitive or irritation-prone skin [35,36]. The fermentation process helps with the breakdown of allergenic proteins and potential irritants, thereby reducing the risk of skin irritation or allergic reactions. Additionally, fermentation results in a more stable, pH-balanced formulation, which is especially advantageous for individuals with skin conditions such as eczema and rosacea. Moreover, fermentation stimulates the production of lactic acid, which not only provides gentle exfoliation but also helps maintain the skin’s natural pH balance [37]. This pH-balancing effect is crucial for supporting the skin’s acid mantle, enhancing its ability to protect against harmful microorganisms and environmental pollutants [38,39,40].

2.2.4. Sustainability and Environmental Benefits

Fermentation provides several ecological advantages over traditional extraction methods. It is inherently more sustainable, requiring fewer resources, such as water and energy, and generating less waste [41]. In contrast to conventional extraction techniques that often depend on harsh chemicals and solvents, fermentation is a more environmentally friendly process [42]. Furthermore, it enables the use of renewable agricultural rice, contributing to the development of eco-conscious skincare formulations. This sustainability not only reduces the environmental footprint of cosmetic production but also aligns with the increasing consumer demand for natural and sustainable ingredients in skincare products.

3. Bioactive Components in RFPs

During fermentation, microorganisms decompose the complex starches in rice, converting them into bioactive compounds. This process notably increases the concentration of bioactive compounds and, in some cases, alters their structural characteristics, thereby enhancing their biological activities. This section explores the key bioactive compounds found in RFPs, including amino acids, peptides, organic acids, polyphenols, polysaccharides, vitamins, and minerals (

Table 1. Key bioactive compounds present in rice fermentation products (RFPs).

Key Bioactive Compounds	General Composition	Typical Compounds
Amino acids	10~30%	Glutamic acid, lysine, glycine, serine
Peptides	5~15%	Glutathione, rice peptides
Organic acids	5~15%	Lactic acid, citric acid, malic acid
Polyphenols	1~5%	Ferulic acid, γ-oryzanol, phytic acid
Polysaccharides	15~30%	Mannan, hyaluronic acid, β-glucans
Vitamins and minerals	1~5%	Vitamin B, vitamin E, Mg, P, Se, Zn

).

3.1. Amino Acids

Amino acids are fundamental building blocks for the synthesis of various proteins in biological organisms, playing a critical role in tissue metabolism, growth, and repair [43]. Moreover, amino acids are hygroscopic compounds that attract and retain water, thereby contributing significantly to maintaining the skin’s natural hydration [44]. During the fermentation process of rice, microorganisms break down rice proteins into smaller peptides and amino acids [45]. Consequently, the fermentation process significantly enhances the levels of various amino acids [46]. The most prominent amino acids present in RFPs include glutamic acid, aspartic acid, alanine, lysine, glycine, γ-aminobutyric acid, and serine, all of which are essential for supporting skin hydration and barrier function [47,48]. In particular, certain amino acids, such as glycine, proline, and hydroxyproline, are critical components for collagen synthesis and play a vital role in maintaining skin health, elasticity, and structural integrity [49,50].

3.2. Peptides

Peptides, short chains of amino acids, are among the most important bioactive components in RFPs [51]. During fermentation, the proteins in rice are degraded into smaller peptides, which exhibit a variety of skin-enhancing properties, such as improving skin hydration, stimulating collagen production, and enhancing skin elasticity [52,53]. Due to their smaller size, these peptides can penetrate the skin barrier more effectively than larger proteins, thereby increasing their bioavailability and potency [54]. A notable example of such peptides in RFPs is bioactive peptides, which possess remarkable antioxidant and anti-inflammatory properties [55]. A study by Mo et al. demonstrated that the fermentation of rice with Lactobacillus plantarum produced a mixture of small peptides, each containing fewer than 11 amino acids [56]. These peptides exhibited strong antioxidant activity, effectively scavenging free radicals, reducing oxidative stress, and thereby preventing premature skin aging.

3.3. Organic Acids

RFPs are rich in various organic acids, including lactic acid, citric acid, malic acid, succinic acid, and butyric acid [57]. These organic acids are essential for exfoliation and moisturization, while also providing skin barrier repair, as well as anti-aging, antioxidant, and anti-inflammatory benefits [58,59]. Furthermore, the organic acids in RFPs help maintain skin pH and exhibit antimicrobial properties that support a balanced skin microbiome by inhibiting harmful bacteria and promoting beneficial microorganisms [60]. Lactic acid, a well-known alpha-hydroxy acid, gently exfoliates the skin and has whitening effects [61]. It enhances epithelial cell metabolism, accelerates the shedding of dead skin cells, promotes skin renewal, and brightens the complexion [62,63]. Another key organic acid, α-ketoglutaric acid, has been shown in numerous studies to possess anti-aging and antioxidant properties, promote collagen synthesis, and support the repair of the skin barrier [64,65].

3.4. Polyphenols

Polyphenols, such as ferulic acid, γ-oryzanol, p-coumaric acids, and phytic acid, are potent antioxidants present in RFPs [66]. These compounds protect the skin from the oxidative stress caused by environmental factors, including UV radiation and pollution [67,68]. By neutralizing free radicals, polyphenols help prevent cellular damage, thereby reducing the risk of premature aging and inflammatory skin conditions [69]. During the fermentation process, these polyphenols are efficiently extracted and concentrated, resulting in a notable increase in total phenolic content and enhanced free radical scavenging activity [6]. A study demonstrated that the fermentation of rice bran by lactic acid bacteria increased the levels of ferulic acid, p-coumaric acid, and γ-oryzanol, thereby boosting antioxidant activity [70]. Li et al. found that ferulic acid, along with flavones such as rutin and apigenin, and flavonols including myricetin, quercetin, and kaempferol, contribute to the antioxidant properties of glutinous rice fermentation, effectively scavenging free radicals [71].

3.5. Polysaccharides

Polysaccharides, due to their hydrophilic nature, effectively attract and retain moisture, making them effective humectants for the skin [72]. Mannan, β-glucans, arabinoxylans, galactomannans, and hyaluronic acid (HA) are the representative polysaccharides found in RFPs [73]. These polysaccharides provide a range of skincare benefits, including antioxidant, anti-inflammatory, immune-modulating, and antimicrobial activities [74,75]. A substantial body of research has shown that fermentation not only increases the total polysaccharide content but also alters the structural characteristics of polysaccharides by breaking down larger polysaccharides into smaller, more bioavailable forms, thereby enhancing their absorption and effectiveness [73]. For instance, β-glucans, which are abundant in RFPs, have been associated with skin repair, anti-inflammatory effects, as well as improved hydration and elasticity [76]. Similarly, HA, recognized for its moisture-retaining properties, helps maintain skin suppleness, smoothness, and elasticity while reducing the appearance of wrinkles [77].

3.6. Vitamins and Minerals

Vitamins and minerals are essential micronutrients that support normal skin physiological functions [78]. A number of studies have confirmed that RFPs are rich in vitamins, including B vitamins and vitamin E, as well as essential trace elements such as magnesium (Mg), phosphorus (P), selenium (Se), zinc (Zn), and iron (Fe) [79]. Notably, during fermentation, microorganisms like lactic acid bacteria can hydrolyze and break down antinutritional factors, thereby enhancing the bioavailability and content of B vitamins and minerals [80]. Niacinamide, a key form of vitamin B, is known to improve skin barrier function, reduce inflammation, and lighten hyperpigmentation [81,82]. Vitamin E, another important vitamin found in RFPs, possesses potent antioxidant properties, helping to protect the skin from UV-induced oxidative damage while promoting wound healing and scar regeneration [83]. Minerals such as Zn and Mg play vital roles in maintaining normal skin function by modulating inflammation, promoting wound healing, and supporting collagen synthesis [84].

4. Skincare Benefits of RFPs

RFPs have garnered significant attention in the cosmetic industry due to their diverse and potent biologically active components. These components offer a multitude of skincare benefits, including enhanced skin hydration, improved barrier function, antioxidant protection, skin whitening, anti-inflammatory effects, and anti-aging properties (Figure 3 and

Table 2. Representative RFPs and their multifaceted skincare benefits at the in vitro and animal levels.

Rice Variety	Main Active Ingredients	Skincare Benefits	Model	Reference
Brown rice	Peptides	Antioxidation	UVA-irradiated mouse model	[56]
Brown rice	Not mentioned	Moisturizing	HaCaT cells	[85]
Red rice	Peptides, polyphenols, amino acids, and vitamins	Moisturizing, skin barrier repair, and antioxidation	HaCaT cells, 3D epidermal models	[86]
Rice	α-ketoglutaric acid	Moisturizing and skin barrier repair	NHEKs cell	[87]
Rice bran	Ferulic acid, arabinose, xylose, and glucose	Antioxidation	DPPH· ABTS+,·OH	[88]
Black rice	Organic acids and phenolic compounds	Whitening	B16F10 melanoma cells	[89]
Rice bran	Polyphenolic compounds	Antioxidation and whitening	DPPH, B16F10 melanoma cells	[90]
Rice bran	γ-aminobutyric acid	Anti-inflammation	LPS-activated macrophage	[91]
Rice bran	Not mentioned	Anti-inflammation	OVA-induced mouse model	[92]
Brown rice	Protein, vitamin, mineral, and polyphenols	Anti-inflammation	IMQ-induced mouse model	[93]
Broken rice	Gallic acid, ascorbic acid, and ferulic acid	UV protection	HSF cells	[94]
Rice	Succinic acid and choline	UV protection and antioxidation	HDF cells	[95]
Rice koji	Fatty acids and phenolic compounds	Anti-aging and antioxidation	HDF cells	[96]
Rice bran	Polyphenolic compounds	Anti-aging and anti-inflammation	HSF cells	[97]
Glutinous rice	Oligosaccharides	Balance the skin microecology	2D and 3D skin models	[98]
Black rice and brown rice	Protein, lipid, and carbohydrate	Balance the skin microecology	In vitro and rats	[99]

). This section delves into the multifaceted effects of RFPs on the skin, supported by in vitro and clinical studies.

4.1. Moisturizing

Moisturization is essential for maintaining skin health, as it strengthens the skin’s natural barrier, prevents dehydration, and protects against external environmental stressors. One of the primary benefits of RFPs is its ability to enhance skin hydration, owing to their rich contents of amino acids, small molecular peptides, polysaccharides, and other effective moisturizing components. A study showed that a brown rice filtrate fermented with Saccharomyces cerevisiae demonstrated the ability to significantly elevate the levels of HA and enhance the expression of hyaluronan synthase 2 and aquaporin 3 (AQP3) in HaCaT cells, both of which are vital for maintaining skin hydration [85]. Similarly, Chen and coworkers employed Aspergillus oryzae for the liquid fermentation of red rice and evaluated the moisturizing benefits of the resulting red rice Aspergillus oryzae fermentation broth [86]. They found that the red rice fermentation broth significantly increased the expression of AQP3, the expression of filaggrin, hyaluronan synthase 1, and AQP3 mRNA, as well as increased the moisture levels in a 3D epidermal model.

4.2. Skin Barrier Repair

The skin barrier serves as the first line of defense for the skin. A healthy skin barrier is crucial for maintaining physiological homeostasis, protecting against external threats, and ensuring optimal hydration and structural integrity [100]. Many studies have demonstrated that rice fermented products can enhance the integrity and function of the skin barrier. Tight junction proteins, including claudins and occludin, play a vital role in maintaining epithelial barrier integrity by regulating cell–cell adhesion and permeability [101]. Yang et al. reported that treatment with a yeast/rice fermentation filtrate significantly increased the protein levels of claudin-1, claudin-4, and occludin in normal human epidermal keratinocyte (NHEK) cells [87]. Additionally, they evaluated the skin-barrier-enhancing effects of the yeast/rice fermentation filtrate in a double-blind, placebo-controlled clinical trial. The results revealed that after applying an emulsion containing rice fermentation filtrate for ten minutes, transepidermal water loss (TEWL) decreased significantly by 25.05%. In another study, Zhou and coworkers identified α-ketoglutaric acid as a key component in a yeast/rice fermentation filtrate, which significantly promoted the mRNA expression of filaggrin, serine palmitoyltransferase, and involucrin—three critical factors involved in maintaining skin barrier integrity [102].

4.3. Antioxidation

Oxidative stress is a key factor in both skin aging and the onset of dermatological disorders. RFPs are rich in antioxidants, including ferulic acid, γ-oryzanol, vitamin E, and antioxidant peptides, which effectively neutralize free radicals and protect the skin from oxidative damage. Chi et al. fermented rice bran with Hypsizigus marmoreus and identified several bioactive compounds, including ferulic acid, arabinose, xylose, and glucose, in the fermentation broth [88]. The in vitro experiments demonstrated that the purified fermentation broth exhibited scavenging rates of 85.43% for hydroxyl radicals, 70.29% for ABTS radicals, and 92.46% for DPPH radicals, which were 1.98, 2.24, and 2.94 times higher, respectively, compared to the unpurified broth. Similarly, Mo et al. fermented rice with Lactobacillus plantarum, resulting in the production of small peptides [56]. This rice fermentation product effectively scavenged reactive oxygen species (ROS) and malondialdehyde, reducing UVA-induced oxidative stress in a human skin fibroblast (HSF) model via the NRF2 pathway. Furthermore, it increased catalase activity, promoting the decomposition of hydrogen peroxide (H₂O₂) and mitigating oxidative stress in UVA-irradiated mice. In this animal model, it also alleviated the skin photoaging induced by UVA radiation and oxidative stress.

4.4. Whitening

Melanogenesis is a complex process involved in the synthesis of melanin pigments, which is the primary cause of skin pigmentation [103]. Sangkaew and collaborators demonstrated that fermented unpolished black rice significantly reduced cellular melanin content and markedly decreased intracellular tyrosinase activity in B16F10 melanoma cells [89]. Furthermore, the fermentation product notably decreased the mRNA and protein expression levels of tyrosinase-related protein 1 and 2 as well as microphthalmia-associated transcription factor (MITF). Chung et al. found that the co-fermentation of rice bran with Lactobacillus rhamnosus and Saccharomyces cerevisiae significantly inhibited α-melanocyte-stimulating hormone (MSH)-induced melanin synthesis and notably reduced MITF expression [90]. Several clinical trials have also reported a significant reduction in hyperpigmentation or a whitening effect following the use of RFPs [15,87,104,105]. For example, Jufri et al. evaluated the efficacy of a lotion containing 10% fermented black rice bran extract in 34 female subjects [104]. After 14 days of use, the lotion significantly reduced both the melanin and erythema on the forearm, indicating its effectiveness in reducing skin melanin production. In another study, Manosroi et al. formulated a cream containing fermented rice bran-encapsulated niosomes, and skin pigmentation changes were evaluated using a mexameter. The results showed that, after 28 days of treatment, skin melanin levels were reduced by a factor of 33.2 compared to the untreated group [105].

4.5. Anti-Inflammation

Inflammatory factors can accelerate the degradation of collagen and elastin fibers while inhibiting their synthesis and regeneration [106]. Chronic inflammation, if prolonged, can also lead to further complications, including pigmentation disorders. RFPs exhibit significant anti-inflammatory properties, primarily due to their rich content of anti-inflammatory peptides and polysaccharides. Ngo et al. reported that an aqueous solution of rice bran fermented with Lactobacillus fermentum decreased the production levels of interleukin-6 (IL-6), IL-1β, tumor necrosis factor-α (TNF-α), and monocyte chemoattractant protein-1 in a lipopolysaccharide (LPS)-activated macrophage model [91]. In another study, Fan et al. evaluated the anti-inflammatory effect of water extracts of fermented rice bran using an ovalbumin (OVA)-induced mouse model [92]. Their findings demonstrated that the fermented rice bran extract significantly reduced the levels of inflammation-related factors, including those of TNF-α, IL-6, interferon-γ (IFN-γ), and interleukin-10 (IL-10). Similarly, Umeyama et al. evaluated the anti-inflammatory effects of fermented brown rice with Aspergillus oryzae on mice using the imiquimod (IMQ)-induced psoriasis model [93]. The findings revealed a significant inhibition of the mRNA expression of IL-17A, IL-1β, and COX-2 in the skin tissue of the mice.

4.6. Ultraviolet Protection

UV radiation causes substantial damage to the skin, leading to DNA mutations, oxidative stress, inflammation, and the degradation of collagen and elastin, all of which contribute to premature skin aging and hyperpigmentation [107]. Due to the presence of various photoprotective compounds, RFPs have been reported to exhibit strong ultraviolet protection properties. Anisah et al. investigated the effects of fermented broken rice (FBR) with Aspergillus oryzae and fermented rice water extract (FBrR) on UVB-irradiated keratinocytes [94]. The results demonstrated that both FBR and FBrR significantly reduced the secretion of matrix metalloproteinase-1 (MMP-1). Additionally, their study found that these rice fermentation extracts also significantly decreased elastase activity, suggesting their potential role in mitigating photoaging by inhibiting elastase activity in UVA-irradiated fibroblasts. Li et al. investigated the effects of yeast/rice fermentation filtrate and its key components on UVA-exposed human dermal fibroblasts (HDFs) [95]. The results revealed that treatment with 1 mg/mL filtrate reduced fibroblast senescence, inhibited MMP-1 expression, and increased the production of glutathione (GSH) and superoxide dismutase (SOD).

4.7. Anti-Aging Effects

Aging skin is characterized by wrinkles, a loss of elasticity, and reduced collagen production [108]. Due to their rich contents of bioactive compounds that promote collagen synthesis and inhibit collagen degradation, RFPs have demonstrated anti-aging effects in numerous in vitro and animal studies as well as in several clinical studies. For instance, JournLee et al. evaluated the anti-aging effects of rice koji fermented with Aspergillus oryzae and Aspergillus cristatus in HDFs [96]. They found that the fermented products significantly increased the RNA expression levels of collagen, elastin, and MMP-1. A study by Seo et al. demonstrated that fermented rice bran extracts enhanced type I collagen synthesis, reduced MMP-1 expression, and suppressed IL-1α production in a photoaged human fibroblast model [97]. Moreover, Mo et al. found that rice fermented with Lactobacillus plantarum protected mice from UVA-induced aging [56]. Histological analysis revealed improvements in skin photoaging, including reduced wrinkles, enhanced collagen organization, and a smoother epidermis, compared to untreated mice. In a randomized controlled trial, Zhou et al. reported that, after 8 weeks of using a face cream containing yeast/rice fermentation filtrate, subjects exhibited significant reductions in the area and length of wrinkles around the eyes as well as improvements in skin firmness and smoothness [102].

4.8. Balance the Skin’s Microecology

The skin microbiome, composed of a diverse array of microorganisms, plays a crucial role in maintaining skin health and homeostasis [109]. Disruptions to this delicate balance can lead to various skin conditions, including acne, eczema, and atopic dermatitis. During rice fermentation, beneficial microorganisms such as Lactobacillus and Saccharomyces are often introduced. These probiotics, along with their metabolites, can positively influence the skin microbiome. An increasing number of studies have demonstrated that RFPs can help balance the skin microbiome by increasing the abundance of beneficial microorganisms while reducing harmful pathogens [98,99,110,111]. For instance, Iemsam-arng et al. investigated the prebiotic potential of fermented glutinous rice filtrate and found that it enhanced the growth of beneficial bacteria (Staphylococcus epidermidis) while inhibiting pathogenic bacteria (Staphylococcus aureus) [98]. In another study, Sutthanut et al. reported that fermented rice bran extracts from black rice and germinated brown rice exhibited antipathogenic activity against Escherichia coli and Staphylococcus aureus [99].

5. Challenges and Limitations of RFPs

Despite their promising bioactive components and multifaceted skincare benefits, the widespread application of RFPs in cosmetic field faces several challenges.

Firstly, ensuring the standardization and consistency of RFPs remains a significant challenge due to the inherent variability in fermentation processes. This process is highly dependent on various factors, including the quality of the raw materials, the specific microbial strains used, and key fermentation parameters such as time, temperature, and pH. Each of these factors can contribute to considerable batch-to-batch variability, complicating the achievement of a consistent final product with uniform smell, texture, and composition. Moreover, RFPs generally contain a wide range of amino acids, peptides, organic acids, and other components, the concentrations of which can fluctuate between batches. This complexity not only complicates standardization but also affects the quality and effectiveness of the final product. Variability in bioactive compound concentrations can lead to inconsistent product performance, undermining consumer trust and regulatory compliance. Additionally, the impurity content in RFPs must be strictly controlled to ensure compliance with safety requirements for cosmetic ingredients. The stringency of regulatory oversight also exacerbates the challenges involved in the production, use, and promotion of RFPs.

Secondly, there is a lack of comprehensive understanding regarding the components and inter-related mechanisms of RFPs. These products often contain a diverse array of amino acids, peptides, organic acids, vitamins, and other bioactive components, making it challenging to determine their precise composition. Advanced analytical techniques, such as high-performance liquid chromatography–mass spectrometry (HPLC-MS) and nuclear magnetic resonance, are required to accurately profile and quantitatively evaluate their chemical composition. Although RFPs have been reported to exhibit skin hydration, antioxidant, anti-inflammatory, and anti-aging properties, the mechanisms underlying these actions remain poorly understood. While several individual bioactive compounds have been identified, their interactions and potential synergistic effects, which are likely critical for modulating biological processes and molecular functions in the skin, have yet to be fully elucidated. A deeper understanding of these interactions is essential to unlock the full therapeutic potential of RFPs in skincare applications.

Thirdly, the existing research on RFPs has been predominantly limited to in vitro studies and a few animal models, with a notable lack of clinical trials involving human subjects. While cell-based and animal studies offer valuable insights into the biological activities and potential benefits of RFPs, they may not fully reflect the complexities of human skin’s responses. The absence of well-designed clinical trials significantly hinders the comprehensive understanding of RFPs’ efficacy, safety, and long-term benefits in practical applications. To bridge this gap, future research must prioritize human clinical studies to validate the promising findings from preclinical models, assess the practical applicability of RFPs in skincare, and explore the potential variability in skin reactions across different populations. Specifically, large-scale, multi-center clinical trials involving diverse age groups, skin types, and geographic regions are essential to ensure the reliability and generalizability of the findings.

Fourthly, the sensory attributes of RFPs, including irritation potential and odor, require further optimization for skincare applications. Although RFPs are generally considered safe and mild, some individuals may experience irritation upon application. This variability in skin reactions can be attributed to factors such as individual sensitivities to specific components in the fermentation products. For instance, preservatives are often added to prevent microbial growth and extend shelf life, but they can be a source of irritation, particularly for sensitive skin. Therefore, developing milder, non-irritating preservatives for use in RFP-based skincare formulations is essential to ensure both safety and quality. Additionally, certain RFPs may have a strong, unpleasant odor, which is often a byproduct of the natural fermentation process, thereby negatively affecting the consumer experience. To enhance sensory appeal, it is vital to optimize the fermentation process and refine the formulation by incorporating odor-masking agents or fragrance-enhancing ingredients.

Taken together, RFPs face challenges related to standardization, component analysis, and the mechanisms of action of their active ingredients, as well as the lack of large-scale clinical evidence and concerns regarding safety and user experience. Addressing these issues is crucial to fully realizing the potential of RFPs in the global skincare market.

6. Future Directions

RFPs have shown considerable potential in skincare, primarily due to their bioactive components. However, to fully exploit these benefits, further advancements are required in several key areas, including advances in fermentation technologies, a deeper understanding of their mechanisms of action, clinical validation, and the integration of emerging scientific fields.

Central to the development of the bioactive compounds in RFPs is fermentation technology, particularly the optimization of microbial strains and fermentation conditions. A promising avenue for future innovation lies in the convergence of synthetic biology, bioinformatics, computational biology, and artificial intelligence (AI), collectively driving the concept of “smart fermentation”. These interdisciplinary technologies enable the optimization of microorganism selection, fine tuning of fermentation conditions, and the alignment of bioactive compounds with specific skincare outcomes. AI and computational tools offer the potential to refine fermentation parameters, not only ensuring consistency and stability but also enhancing the efficacy of RFPs. Moreover, the integration of high-throughput screening and automated systems can improve the reproducibility and scalability of fermentation processes, facilitating more-efficient large-scale production.

Further research is needed to better understand the mechanisms at the molecular level and to determine the optimal combinations and concentrations of bioactive compounds to improve skincare efficacy and for the development of more effective RFPs. The integration of bioinformatics with advanced 3D skin models offers valuable insights into how RFPs interact with the skin. This approach enables the precise identification and targeting of bioactive compounds to address specific skin concerns, such as dryness, pigmentation, and acne. By leveraging these technologies, personalized skincare formulations can be developed to meet individual needs, considering factors such as skin type, age, and specific concerns. This strategy holds great potential for enhancing the therapeutic efficacy, quality, and precision of fermented-rice-based skincare products.

Another promising development is the integration of RFPs with microbiome science. As research into the skin microbiome advances, it has become increasingly evident that a balanced microbial community is crucial for maintaining healthy skin. RFPs, especially those containing probiotics, can support the skin’s microbiome by promoting beneficial microorganisms and inhibiting harmful ones. Moreover, this innovative integration aligns with the growing trend in personalized skincare, as microbiome-targeted treatments could be tailored to an individual’s unique skin composition and needs. By focusing on the skin’s microbial health, fermented-rice-based skincare products hold the potential to offer more holistic, sustainable, and effective solutions for a wide range of skin conditions.

While in vitro and animal studies have shown promising results, large-scale, long-term clinical trials are essential to validate the efficacy and safety of RFPs across diverse populations. Conducting extensive clinical studies involving various age groups, skin types, and geographical regions is necessary to establish reliable data on the safety and efficacy of these products. Such studies will provide robust evidence to support the skin benefits of fermented-rice-based skincare. The continued development of RFPs has the potential to revolutionize skincare regimens, offering more effective, sustainable, and personalized solutions globally.

7. Conclusions

Microbial fermentation provides an environmentally friendly approach to enhance the value of rice by increasing the production of bioactive compounds, improving their bioavailability and reducing skin irritation. RFPs have demonstrated great promise as cosmetic ingredients due to their rich array of bioactive compounds, including amino acids, peptides, organic acids, polyphenols, polysaccharides, vitamins, and minerals. These compounds provide a wide range of skincare benefits, such as moisturizing, skin barrier repair, as well as antioxidant, anti-inflammatory, brightening, and anti-aging effects. While preliminary studies have obtained encouraging results, further research is needed to optimize production standardization, refine component analysis, elucidate their mechanisms of action, and establish large-scale clinical trials to support their efficacy and safety. As research advances, RFPs are expected to play a pivotal role in the cosmetics industry, offering natural and effective solutions for promoting skin health.