Nanotechnology-Based Herbal Sunscreens: Current Trends, Challenges and Future Perspectives

One of the most common environmental insults to human skin is ultraviolet (UV) radiation from the sun. The solar UV spectrum, which is divided into UVA (320–400 nm), UVB (280–320 nm), and UVC (<280 nm), mediates a variety of biological consequences, from the production of helpful vitamin D3 to harmful DNA damage, immunosuppression, photoaging, and carcinogenesis [1,2]. The World Health Organization estimates that over 1.5 million new cases of skin cancer occur globally each year, a burden that is disproportionately linked to prolonged sun exposure [3]. The incidence of both melanoma and non-melanoma skin cancers is rising at an alarming rate. Historically, synthetic UV filters including avobenzone, oxybenzone, octocrylene, and octinoxate have been used in conventional sunscreen formulas. Even though these compounds are effective at reducing UV radiation, there has been a lot of scientific and regulatory attention due to growing concerns about systemic absorption, endocrine disruption, coral reef damage, and contact sensitization [4,5]. In its 2019 proposed regulation, the US Food and Drug Administration (FDA) noted that out of 16 approved filters, only zinc oxide and titanium dioxide were GRASE (Generally Recognized as Safe and Effective), highlighting the need for safer substitutes [6]. With several modes of action, such as UV absorption, free radical scavenging, anti-inflammatory activity, and DNA repair facilitation, herbal photoprotective agents—which are derived from plant secondary metabolites like flavonoids, polyphenols, carotenoids, and tannins—represent an appealing natural substitute [7,8]. Nevertheless, many phytoconstituents have intrinsic drawbacks that limit their medicinal use as independent sunscreen agents, such as hydrophobicity, photolability, poor and unpredictable skin penetration, and chemical instability [9]. A paradigm-shifting strategy to deal with these biopharmaceutical issues is nanotechnology. Improved skin penetration, increased photostability, controlled and sustained release, targeted delivery to skin layers, and increased Sun Protection Factor (SPF) values can all be achieved at the same time by encasing herbal actives within engineered nanocarriers at the 1–1000 nm [10,11]. Thus, the discipline of nanophytocosmetics a fast developing topic with significant implications for dermatology and cosmetic science was created by the intersection of herbal pharmacognosy and nanotechnology. The current review thoroughly looks at the following topics: (i) skin structure and UVmediated damage mechanisms; (ii) herbal photoprotective agents and their phytochemical basis; (iii) the types of nanocarriers used and their rationale; (iv) formulation strategies and evaluation methodologies; (v) recent clinical and experimental findings; (vi) regulatory considerations; and (vii) future perspectives, including green nanotechnology and AI driven formulation design.

SKIN STRUCTURE AND UV RADIATION

STRUCTURE OF SKIN

The epidermis, dermis, and subcutaneous tissue (hypodermis) are the three main layers that make up human skin, which is the biggest organ in the body at 1.5–2.0 m². Each of these layers has a unique function in photoprotection [12]

The five sublayers of the stratified squamous epithelium that make up the epidermis are stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum Basale. The primary physicochemical barrier to transdermal penetration is the stratum corneum, which is made up of 15–20 layers of anucleate corneocytes embedded in a lipid matrix. Over 95% of epidermal cells are keratinocytes, which undergo a 28-day cycle of increasing differentiation from the basal layer to the surface. Melanocytes are found in the stratum Basale at a ratio of roughly 1:10 to keratinocytes. They produce melanin pigment in specialized organelles called melanosomes, which are then transported to keratinocytes to create supranuclear caps that protect DNA from ultraviolet light [13].

The dermis, which contains collagen (Type I and III), elastin, glycosaminoglycans, fibroblasts, mast cells, and a rich vascular network, supports the epidermis both structurally and nutritionally. By activating matrix metalloproteinase (MMP), collagen, which makes up 70–80% of the dry weight of the skin, is the main target of UV-induced photoaging [14]. Adipocytes and loose connective tissue make up the hypodermis, which serves as a mechanical cushion, thermal insulator, and energy storage. Multiple interconnected biochemical pathways that work in concert to induce skin damage are mediated by UV radiation [16, 17]:

TYPES OF UV RADIATION

According to wavelength and biological activity, solar UV radiation that reaches the Earth's surface is typically divided into three physiologically significant bands [15]:UVA (320–400 nm): Approximately 95% of solar UV that reaches the Earth's surface is in this range. Deeply penetrating the dermis, UVA causes oxidative damage mainly by producing reactive oxygen species (ROS). By indirectly damaging DNA through photosensitization reactions, it promotes tanning, photoaging, and carcinogenesis.

• UVB (280–320 nm): Approximately 5% of solar UV reaches the surface of the Earth. DNA directly absorbs UVB, which causes 6-4 photoproducts (6-4PPs) and cyclobutane pyrimidine dimers (CPDs), the main photolesions that initiate skin cancer. The epidermis is the primary absorber of UVB rays.

• UVC (<280 nm): Under typical meteorological conditions, it is entirely absorbed by stratospheric ozone and does not make it to the Earth's surface. Erythema and severe keratitis can be caused by artificial UVC sources, such as germicidal lamps.

MECHANISMS OF UV INDUCED SKIN DEMAGE 

Multiple interconnected biochemical pathways that work in concert to induce skin damage are mediated by UV radiation [16, 17]: Oxidative Stress: ROS such as singlet oxygen (1O2), superoxide anion (O2), hydrogen peroxide (H2O2), and hydroxyl radical (OH) are produced by UVA and UVB. Lipid membranes, proteins, and nucleic acids are oxidized by ROS, which overwhelms the body's natural antioxidant defence’s, such as glutathione peroxidase, catalase, and superoxide dismutase [18].

DNA Damage: UVB directly causes CPDs and 6-4PPs at dipyrimidine sites, which can lead to mutagenic C→T and CC→TT transition mutations in tumour suppressor genes, such as TP53, if they are not fixed by nucleotide excision repair (NER) mechanisms [19]. UVA mostly results in 8-oxo-7,8-dihydroguanine (8-oxoG) oxidative DNA damages, which produce G→T transversions [20].

Photoaging: Prolonged exposure to UV light activates nuclear factor-kB (NF-kB) and activator protein-1 (AP-1) transcription factors, upregulating matrix metalloproteinases (MMP-1, MMP-3, and MMP-9) that break down dermal collagen and elastin, resulting in the clinical phenotype of photoaged skin, which includes wrinkles, laxity, telangiectasias, and dyspigmentation [21].

Skin cancer: The main carcinogenic pathways include UV-induced mutations in TP53 (basal cell carcinoma, squamous cell carcinoma) and BRAF pathway activation (melanoma). Immune surveillance of transformed cells is further compromised by immunosuppression caused by UV-damaged keratinocytes that release prostaglandins, IL10, and cis-urocanic acid [22].

HERBAL AGENTS USED IN SUNSCREENS

 ROLE OF PHYTOCONSTITUENTS IN PHOTOPROTECTION

Over millions of years, plants have developed complex UV defence mechanisms by accumulating a variety of secondary metabolites that both absorb UV light and neutralize ROS. Beyond just UV filtering, these phytoconstituents offer a multifunctional approach to photoprotection [23, 24]: Flavonoids: This structurally varied class of polyphenols, which includes isoflavones, flavones, flavonols, and flavanones, has distinctive chromophoric systems that allow UV absorption in the 280–350 nm range. Strong anti-inflammatory and antioxidant properties are exhibited by quercetin, kaempferol, and luteolin by direct ROS scavenging, COX-2 suppression, and inhibition of NF-kB signaling [25].

Polyphenols: Resveratrol, rosmarinic acid, chlorogenic acid, and ellagic acid are significant photoprotective polyphenols. While resveratrol stimulates SIRT1 deacetylase, a regulator of DNA repair and cellular stress responses, ellagic acid suppresses MMP-1 production and melanogenesis [26]

Tannins: Condensed tannins (proanthocyanidins) and hydrolyzable tannins (gallotannins, ellagitannins) absorb UV light and show metal chelation activity, which lowers the production of hydroxyl radicals caused by the Fenton reaction. In animal models, grape seed proanthocyanidins show strong UVB protection [27].

Terpenoids: Triterpenoids (ursolic acid, oleanolic acid) and carotenoids (beta-carotene, lycopene, astaxanthin) act as membrane stabilizers and UV absorbers. Singlet oxygen is quenched by carotenoids at a rate constant of around 3×10^10 M-1s-1 [28].

Carotenoids: UV-absorbing pigments and broad-spectrum antioxidants include lycopene, beta-carotene, and astaxanthin. In singlet oxygen quenching, astaxanthin has ten times the antioxidant activity of beta-carotene [29].

COMMON HERBAL PHOTOPROTECTIVE AGENTS

A thorough list of important herbal photoprotective agents and their main active ingredients is given in Table 1. The most extensively researched agents' brief profiles are shown below:

Table 1: Herbal Agents, Active Phytoconstituents, and Photoprotective Activities

Aloe vera (Aloe barbadensis Miller) is a succulent plant with a long history of use in ethnomedicine for photoprotection. Acemannan, a beta-1,4-acetylated mannan, aloin, aloeemodin, and flavonoids are all present in the mucilaginous gel. Aloe vera has been shown to have anti-inflammatory, wound-healing, moisturizing, and UVB-attenuating characteristics in clinical settings. These effects are partly explained by the suppression of the thromboxane A2 pathway and the encouragement of fibroblast proliferation [30].

Curcuma longa (turmeric): The rhizome of this Zingiberaceae member produces curcuminoids (75–80% curcumin, 15–20% bisdemethoxycurcumin, and 5% demethoxycurcumin) with strong UV absorption at 430 nm, anti-inflammatory qualities through inhibition of the NF-kB and MAPK pathways, and photoprotective activity against UVB-induced DNA damage [31].

Camellia sinensis, or green tea: Packed in catechin polyphenols, especially (−)epigallocatechin-3-gallate (EGCG), which at 10 µM suppresses the activation of AP-1 and NF-kB caused by UVB. In human volunteers, topical EGCG treatment decreases UVBinduced erythema and CPD development [32].

Pomegranates (Punica granatum): Punicalagins, ellagic acid, and anthocyanins are abundant in fruit extracts. These substances prevent MMP activity, melanogenesis, and DNA damage brought on by UVB. In vitro, pomegranate peel extract has estimated SPF values of 12–18 [33]

MECHANISM OF HERBAL PHOTOPROTECTION

Herbal medicines' photoprotective action functions via four complimentary, frequently synergistic mechanisms [34, 35]:

• UV Absorption: Flavonoids and polyphenols' aromatic chromophoric complexes absorb UV photons and release energy as heat through excited-state deactivation, which stops UVinduced photochemical reactions in skin biomolecules

• Antioxidant Activity: Hydrogen atoms are donated by phenolic -OH groups to stop ROS chain reactions. Resonance delocalization stabilizes the resultant phenoxyl radicals, preventing them from being sufficiently reactive to spread harm.

• Free Radical Scavenging: Direct quenching of reactive species (1O2, •OH, O2•−, ONOO−) by hydrogen atom transfer (HAT), metal chelation, and electron donation

• Anti-inflammatory Activity: By suppressing prostaglandin, leukotriene, and cytokine synthesis in UV-exposed skin, inhibition of the COX-2, LOX, iNOS, and NF-kB pathways reduces erythema, oedema, and immunological suppression.

NANOTECHNOLOGY IN HERBAL SUNSCREENS

INTRODUCTION TO NANOTECHNOLOGY

The engineering, characterization, and use of materials and devices with at least one dimension in the range of 1–100 nm (or, more generally, up to 1000 nm for pharmaceutical systems) constitute nanotechnology. When compared to their bulk counterparts, materials at the nanoscale display significantly different physicochemical characteristics, such as quantum effects, an increased surface-to-volume ratio, improved reactivity, and modified solubility [36].

In the context of dermal drug delivery, nanotechnology confers several pharmacokinetic and pharmacodynamic advantages: enhanced permeation through the stratum corneum via follicular and intercellular routes, improved solubility of lipophilic actives, protection from environmental degradation, sustained and controlled release, and targeted delivery to specific skin compartments [37].

ADVANTAGES OF NANO HERBAL SUNSCREENS

• Enhanced SPF: By improving dispersion and reducing particle size, nanoencapsulation increases the effective UV-absorbing surface area of herbal actives, allowing for better SPF values at equal active doses. SPF values for nano-curcumin formulations are three to four times greater than those for bulk curcumin preparations [38].
• Better Skin Penetration: Nanoparticles (10–300 nm) transport active ingredients to viable epidermis and dermis where photoprotection is required by penetrating the stratum corneum through the transfollicular, intercellular lipid, and disturbed barrier areas [39].
• Enhanced Photostability: By limiting direct photon exposure, encapsulation protects labile phytoconstituents from photodegradation. In comparison to free curcumin, curcumin stability in nanoemulsions is significantly enhanced during UV irradiation [40].
• Controlled Release: By allowing for sustained release over 8–12 hours, matrix or reservoir nanocarrier topologies lower the frequency of reapplication while preserving protective concentrations [41].
• Enhanced Bioavailability: By overcoming solubility constraints, nanoencapsulation raises the percentage of active ingredients that are accessible for skin contact. EGCG skin absorption is increased by four to five times using phytosome technology [42].
• Aesthetic Acceptability: Transparent or translucent nanoparticles in the 20–50 nm range do not have the whitening impact of traditional mineral sunscreens.

TYPES OF NANOCARRIERS USED IN HERBAL SUNSCREENS

• For the delivery of herbal sunscreen, a wide range of nanocarrier platforms have been studied; each has unique structural traits, loading capabilities, and release patterns. A comparative overview is given in Table 2.

Table 2: Nanocarriers Used in Herbal Sunscreen Formulations – Comparison

NANOEMULSION

Nanoemulsions are thermodynamically or kinetically stable, optically isotropic disperse systems consisting of two immiscible liquids (typically oil and water) stabilized by a surfactant/cosurfactant interfacial film, with droplet sizes in the 20–500 nm range [43]. They are classified as oil-in-water (O/W) or water-in-oil (W/O) based on the dispersed phase. Their high surface area, low interfacial tension, and ability to solubilize lipophilic actives make them ideal vehicles for herbal phytoconstituents. Preparation methods include highpressure homogenization, microfluidization, and spontaneous emulsification. Curcumin nanoemulsions have demonstrated SPF values up to 42 with UVA:UVB critical wavelength ratios indicating broad-spectrum protection [44].

LIPOSOMES

Liposomes are spherical, self-assembling vesicles with sizes ranging from 25 nm to several micrometers that are made up of one or more concentric phospholipid bilayers encasing an aqueous core [45]. Hydrophilic (aqueous core) and lipophilic (bilayer) herbal actives can be encapsulated simultaneously thanks to their amphiphilic architecture. They have superior biocompatibility and skin compatibility since their composition resembles biological membranes. For the delivery of macromolecular polyphenols like resveratrol and EGCG, deformable liposomes (transfersomes, ethosomes) with improved skin penetration show great promise [46].

SOLID LIPID NANOPARTICLES (SLN)

A solid lipid core (physiological lipids like stearic acid, cetyl palmitate, or beeswax) stabilized by an emulsifier monolayer makes up SLN, which was first developed in the early 1990s [47]. Superior chemical protection of encapsulated actives, regulated release, occlusive skin moisturization, and UV-scattering qualities that add extra SPF are all provided by the solid matrix. SLN are scalable for industrial production and can be created by either hot or cold homogenization. Drug ejection during lipid polymorphism transitions from the α to the more ordered β crystalline form is one of the main limitations [48].

NANOSTRUCTURED LIPID CARRIERS(NLC)

In order to produce structural disorder that allows for increased drug loading and minimizes polymorphic transitions seen in SLN, NLC, a second-generation lipid nanoparticle idea, incorporates a combination of solid and liquid lipids in the core matrix [49]. There are three types of structural models: the numerous type (oil nano compartments within solid lipid), the amorphous type (no crystalline structure), and the imperfect type (spatially flawed crystals). When compared to both free actives and SLN, NLC including curcumin, quercetin, and pomegranate extracts has shown noticeably improved photostability and SPF [50].

POLYMERIC NANOPARTICLES

Biodegradable polymers including poly(lactic-co-glycolic acid) (PLGA), polylactic acid (PLA), chitosan, and poly(epsilon-caprolactone) (PCL) can be used to manufacture polymeric nanoparticles (50–500 nm) as nanospheres (matrix systems) or nanocapsules (core-shell systems) [51]. Because of their mucoadhesive qualities, innate antibacterial activity, and capacity to form ionic complexes with anionic polyphenols, chitosan nanoparticles are very appealing for herbal administration. EGCG encapsulated in PLGA exhibits prolonged release over a 72-hour period while maintaining its antioxidant efficacy [52].

PHYTOSOMES

Polar phytoconstituents and phosphatidylcholine produce a 1:1 or 1:2 molar complex by coordinate covalent bonding in phytosomes (herbosome technology, Indena S.p.A.) [53]. Transcutaneous absorption is greatly improved by this complexation, which changes the hydrophilic polyphenol into a more lipophilic, membrane-compatible molecule. In comparison to uncomplexed extracts, green tea phytosomes, quercetin phytosomes, and grape seed proanthocyanidin phytosomes have shown gains in skin bioavailability of three to five times [54].

NANOGELS

Particle sizes in the 100–1000 nm range are found in nanogels, which are three-dimensional crosslinked polymeric networks inflated with solvent [55]. They have adjustable mechanical characteristics, a high water content (which makes them aesthetically pleasing), and the capacity to react to environmental cues (pH, temperature, ionic strength). Excellent spreadability, stability, and moderate SPF values have been shown by carbopol and HPMC based nanogels containing aloe vera and neem extracts (28–35) [56].

METALLIC NANOPARTICLES

Through both absorption and scattering mechanisms, inorganic metallic nanoparticles in particular, zinc oxide (ZnO) and titanium dioxide (TiO2) act as physical/mineral UV blockers. Compared to their micronized counterparts, they offer better cosmetic transparency and broad-spectrum UVA/UVB protection at the nanoscale (10–50 nm) [57]. Additionally, ZnO nanoparticles exhibit inherent antifungal and antibacterial qualities. Green nanotechnology and herbal pharmacognosy have come together to create green-synthesised ZnO and AgNPs utilizing plant extracts (neem, aloe vera, tulsi), where phytoconstituents act as both reducing/capping agents and photoprotective agents [58].

FORMULATION STRATERIGES NANO HERBAL SUNSCREENS

SELECTIONS OF HERBAL EXTRACTS

The following factors must be carefully taken into account when choosing herbal extracts for nanoformulation: (i) phytochemical standardization (HPLC marker compound quantification); (ii) UV absorption spectrum (identification of chromophoric constituents); (iii) antioxidant capacity (DPPH, FRAP, ABTS assays); (iv) physicochemical compatibility with chosen excipients; and (v) safety profile (cytotoxicity, allergenicity, phototoxicity data) [59]. Batch-to-batch repeatability, which is necessary for regulatory compliance, is ensured by standardized extracts represented as marker chemical equivalents (e.g., % curcumin, % EGCG, % quercetin).

PREPARATION TECHNIQUES

High-Pressure Homogenization (HPH): Uses cavitation, turbulence, and shear forces to reduce droplet/particle size by applying pressure differentials of 200–1500 bar. While cold HPH is better for thermolabile actives, hot HPH is used for SLN preparation (melted lipids, distributed in hot aqueous surfactant solution, homogenized at increased temperature). Narrow size distributions (PDI <0.2) are produced by HPH, which is scalable in the industrial setting [60].

Ultrasonication (Probe Sonication): Localized energy densities produced by acoustic cavitation are high enough to break apart interfacial layers and reduce particle size to nanoscale dimensions. extensively employed in the creation of nanoemulsions. Localized heat production and possible metal contamination from probe tip degradation are limitations that are addressed by titanium probe replacement schedules and pulse mode operation [61].

Solvent Evaporation/Emulsion Diffusion: This process involves dissolving lipophilic agents in a volatile organic solvent (such as ethanol or acetone), emulsifying the mixture into the aqueous phase, and then removing the solvent under low pressure. extensively utilized in the synthesis of lipid and polymeric nanoparticles (PLGA, PLA). Pharmaceutical applications require residual solvent monitoring using GC headspace analysis [62].

Microfluidization: A high-pressure method that creates very homogeneous nanodroplets (50200 nm) by repeatedly impinging emulsions at high speeds using an interaction chamber with fixed geometry microchannels. especially well-suited for producing nanoemulsions on a large scale with high consistency [63].

EVALUATION PARAMETERS

 PHYSICOCHEMICAL  EVALUATION

Particle Dimensions and Polydispersity Index (PDI): The most used method for determining particle size is dynamic light scattering (DLS), which measures hydrodynamic diameter in the range of 1-6000 nm. Pharmaceutical nanoparticles are deemed acceptable if their PDI is less than 0.3. Complementary information on size and concentration is provided by Nanoparticle Tracking Analysis (NTA). Sunscreen nanocarrier acceptable ranges are usually between 20 and 500 nm [67].

Zeta Potential: Electrophoretic light scattering is used to quantify electrostatic surface charge, which is a predictor of colloidal stability. Adequate electrostatic stability against aggregation is indicated by absolute zeta potential values greater than ±30 mV. Steric stabilization with PEGylated or polymeric surfactants may be necessary for values between ±10–30 mV [68].

Entrapment Efficiency (%EE) is computed as [(total drug − free drug)/total drug] × 100 after the encapsulated and free active are separated using ultracentrifugation, ultrafiltration, or dialysis. For topical treatments, values greater than 70% are typically regarded as acceptable [69].

PHOTOPROTECTIVE EVALUATION

The Mansur equation is used to compute the in vitro SPF spectrophotometrically: SPF = CF × Σ[E(λ) × I(λ) × Abs(λ)], where E(λ) is the erythemal action spectrum, I(λ) is the sun spectral irradiance, Abs(λ) is the absorbance, and CF is a correction factor (10). By simulating surface roughness, the PMMA (polymethylmethacrylate) plate method (ISO 24443) more closely resembles in vivo circumstances [70]. In vivo SPF is determined using minimal erythema dose (MED) measurement in human volunteers in accordance with ISO 24444:2010.

nm (FDA criteria). The in vitro UVAPF method or the persistent pigment darkening (PPD) method (ISO 24442) are used to calculate the UVA Protection Factor (UVAPF). UVAPF ≥1/3 of SPF is required by EU rules for a broad-spectrum claim [71].

ADVANCED CHARACTERIZATION 

FTIR (Fourier Transform Infrared Spectroscopy): Determines the polymorphic state of lipid nanoparticles (crystallinity index from CH2 scissoring bands at ~1473 and ~1462 cm-1), encapsulation evidence (change in typical phytoconstituent peaks), and functional group interactions. For SLN/NLC characterisation, quantitative information on lipid crystallinity, melting enthalpy, and phase transitions is provided by Differential Scanning Calorimetry (DSC) [72]. Surface topography and spherical nanoparticle structure are morphologically confirmed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). X-ray diffraction (XRD) distinguishes between the crystalline and amorphous states of encapsulated active ingredients [73].

RECENT RESEARCH STUDIES AND MARKETED PRODUCTS

The creation and characterisation of herbal sunscreens based on nanotechnology are documented in a rapidly growing body of research. Table 4 contrasts the benefits and drawbacks of nanocarriers for herbal uses, whereas Table 3 provides a curated summary of representative recent formulation research.

Table 3: Recent Research Studies – Nano Herbal Sunscreen Formulations with SPF Values

Table 4: Advantages and Disadvantages of Nanocarriers for Herbal Sunscreen Applications

1. hybrid nanocarrier systems that combine organic carriers with inorganic UV-filters (e.g., SLN + TiO2) to achieve SPF values >50 with broad-spectrum protection; (ii) the increasing use of QbD and RSM for systematic optimization; (iii) the investigation of biopolymer-based carriers (chitosan, zein, gliadin) from renewable sources; (iv) the incorporation of photostabilizers (avobenzone, UV-quenchers) in herbal nanoformulations for use in aquatic and sports [74,75].

COMMERICAL HERBAL NANO SUNSCREENS

Commercialization of nano-based herbal sunscreens is still in its infancy, with the majority of products using nano-minerals (ZnO, TiO2) in combination with herbal extracts instead of phytoconstituents that are actually nano-encapsulated. Notable commercial brands and products include Badger Balm (nano-ZnO with herbal extracts), Coola Suncare (aloe vera and green tea), and several Ayurvedic brands (Himalaya, Forest Essentials) that use innovative delivery technologies to combine aloe vera, neem, and turmeric. The market for natural and organic sunscreen was estimated to be worth USD 3.2 billion in 2023, and it is expected to expand at a compound annual growth rate (CAGR) of 8.5% through 2030 due to the high demand from consumers for clean-label, environmentally friendly photoprotection [76].

REGULATORY AND SAFETY ASPECTS

   SAFETY CONCERNS OF NANOPARTICLES

Three main factors must be considered when evaluating the safety of nanoparticles used in cosmetic applications: photocatalytic activity, nanotoxicity, and skin penetration [77]. Regarding dermal penetration, the scientific consensus from multiple human and animal studies indicates that ZnO and TiO2 nanoparticles do not penetrate through intact stratum corneum to reach viable skin layers, and systemic absorption is negligible [78]. However, further research is necessary to understand penetration via follicular routes and weakened barriers (eczema, psoriasis, abraded skin).

The lipid and phospholipid components of organic nanocarriers (nanoemulsions, liposomes, SLN) are widely acknowledged as biocompatible; their nanotoxicity has been thoroughly investigated. Cationic polymeric nanoparticles (poly-L-lysine, CTAB-capped systems) and metallic nanoparticles are the main sources of cytotoxicity concerns because they can disrupt mitochondrial membrane potential and cause apoptosis at high concentrations [79].

REGULATORY GUIDELINES

Table5summarizes the regulatory frameworks governing nano-basedherbal                                                                       herbal sunscreens across major jurisdictions

Table 5: Regulatory Frameworks for Nano Herbal Sunscreens