A Comprehensive Review on Sunscreen: Guidelines and Natural Alternatives

Table1. Classification of sunscreen agents

 Mechanism of Phyto-Photoprotection:

Phyto- photoprotection refers to the use of plant-derived bioactive compounds that protect the skin from the harmful effects of ultraviolet (UV) radiation.[5] When skin is exposed to UV rays, it generates reactive oxygen species (ROS), which accelerates photoaging, triggers inflammation, and may contribute to skin carcinogenesis[6]. Plants naturally synthesize secondary metabolites such as flavonoids, terpenoids, phenolic acids, glycosides, and carotenoids to defend themselves against sunlight [7]. These phytochemicals exhibit UV-absorbing, antioxidant, anti-inflammatory, and free-radical scavenging activities, making them valuable in sunscreen formulations. Flavonoids and polyphenols absorb UV-A and UV-B wavelengths, thereby reducing erythema and DNA damage [8]. Terpenoids and carotenoids help stabilize cell membranes, prevent collagen degradation, and reduce oxidative stress in the dermis. Due to their biodegradability, biocompatibility, and low toxicity, plant-based sunscreen agents are considered safer alternatives to purely synthetic UV filters [9]. Hence, herbal or phyto-enhanced sunscreens are being widely studied for their potential to provide broad-spectrum, antioxidant-rich sun protection with minimal side effects [10] .

1. Antioxidants:

Antioxidants are one of the most important classes of phytochemicals used in sunscreen formulations because they directly counteract the oxidative damage caused by ultraviolet radiation. When the skin is exposed to UV-A (320–400 nm) and UV-B (280–320 nm) rays, it leads to the formation of reactive oxygen species (ROS), such as superoxide radicals, singlet oxygen, and hydroxyl radicals [11]. These ROS attack structural proteins like collagen and elastin, damage cellular lipids, and break DNA strands, resulting in premature aging, inflammation, pigmentation, and sometimes carcinogenesis. Plant-derived antioxidants including Vitamin C (ascorbic acid), Vitamin E (tocopherols), phenolic acids, polyphenols, carotenoids, and green tea catechins help neutralize these radicals by donating hydrogen atoms or electrons to stabilize them [12].

2. Flavonoids:

Flavonoids are a large class of polyphenolic secondary metabolites widely distributed in fruits, vegetables, teas, and medicinal plants. Their chemical structure contains conjugated aromatic rings, enabling them to absorb UV light, particularly in the UV-B region, thereby functioning as natural UV filters. Examples include quercetin, rutin, kaempferol, catechins (in green tea), naringenin (in citrus), and apigenin (in chamomile).In addition to UV absorption, flavonoids show strong antioxidant and anti-inflammatory activities. They inhibit the activation of matrix metalloproteinases (MMPs), enzymes responsible for breaking down collagen and elastin, thus preventing wrinkles and loss of skin elasticity [13]

3. Terpenoids:

Terpenoids (also known as isoprenoids) represent another major class of phytochemicals with photoprotective benefits. These compounds are derived from isoprene (C5H8) units and are commonly found in essential oils, resins, citrus peels, neem, turmeric, and many herbal plants. Common photoprotective terpenoids include lutein, β-carotene, limonene, menthol, and α-pinene  [14].Terpenoids exhibit membrane-stabilizing and antioxidant activities, protecting skin cells from ROS-mediated oxidative damage. Carotenoids like lutein and β-carotene accumulate in the epidermis and dermis, reducing the intensity of erythema after UV exposure, essentially acting as internal sunscreen agents. They also prevent collagen degradation, reduce inflammation, and promote tissue repair by enhancing fibroblast activity. Therefore, terpenoids not only protect the skin from oxidative damage but also help maintain structural integrity and smooth texture [15].

4. Amino Acid Derivatives

Amino acids and their derivatives are natural components of the Natural Moisturizing Factor (NMF) present in the skin. Examples include histidine, cysteine, glycine, proline, and tyrosine. These molecules play key roles in hydration, protein synthesis, and tissue repair. During UV exposure, protein structures undergo denaturation and generate acidity in the skin environment (16). Amino acids help restore pH balance, improve barrier function, and support the regeneration of structural proteins like collagen and keratin.Some amino acids (e.g., histidine and cysteine) have antioxidant potential because they can chelate metal ions and neutralize ROS. Tyrosine acts as a precursor in melanin synthesis, providing natural photoprotection by enabling controlled tanning and reducing sunburn sensitivity [17]. Thus, amino acid derivatives contribute not only to skin hydration but also to recovery and repair following UV damage.

5. Glycosides

Glycosides consist of a bioactive aglycone component bound to a sugar moiety. This structure enhances their stability, solubility, and skin penetration, making them valuable in dermatological formulations. Many flavonoids exist naturally in glycosylated forms, such as rutin, which shows anti-inflammatory, vasoprotective, and antioxidant activities [17]. Salicin, a glycoside from Salix alba (willow bark), exhibits anti-inflammatory and soothing properties, reducing erythema and irritation caused by sun exposure. Glycosides reduce UV-mediated inflammation by inhibiting COX-2 and NF-κB pathways, which are responsible for inflammatory signaling. They also help maintain collagen and elastin structure, preventing wrinkle formation and loss of elasticity. Due to these mechanisms, glycosides are increasingly being incorporated into herbal sunscreen and anti-aging formulations [18].

Natural Alternatives:

Table No.2. Examples of plants containing Antioxidants and its role in skin protection

Table No.3. Examples of plants containing Flavonoids and its role in skin protection

Table No. 4 .Examples of plants containing Glycosides and its role in skin protection

Table No. 5. Examples of plants containing Terpenoids and its role in skin protection.

Sunscreen Regulations and Their Governing Acts: [19]

• India cosmetic regulation :

 In India, cosmetic products are regulated under the Drugs and Cosmetics Act, 1940, which provides the legal framework for defining cosmetics, regulating their manufacture and sale, and preventing misbranding and adulteration. The Cosmetics Rules, 2020, consisting of 72 rules and 13 schedules, prescribe requirements for the manufacture, testing, labeling, import, registration, sale, and distribution of cosmetics. These rules were further revised through the Cosmetics (Amendment) Rules, 2025, to clarify various provisions and improve regulatory compliance across the supply chain. The Legal Metrology (Packaged Commodities) Rules, 2011, with the latest amendments effective from 1 January 2024, specify mandatory labeling and packaging requirements for cosmetic products. In addition, the Bureau of Indian Standards (BIS) has issued IS 4707 (Part 1): 2020, which lists colorants generally recognized as safe (GRAS) for cosmetic use; IS 4707 (Part 2): 2017, which classifies ingredients not generally recognized as safe (GNRAS), restricted substances, permitted preservatives, and UV filters with specified conditions; and IS 4707 (Part 4): 2022, which provides the updated list of permitted UV filters with restrictions. This standard incorporates the UV filter list previously included in Annex D of IS 4707 (Part 2): 2017 and aligns Indian regulations with EC Regulation 1223/2009.

• Australian sunscreen regulation:

Australian Cosmetic and Sunscreen Regulation: In Australia, cosmetic sunscreens are regulated under the Industrial Chemicals Act 2019 through the Australian Industrial Chemicals Introduction Scheme (AICIS), while ingredient labeling is governed by the Consumer Goods (Cosmetics) Information Standard 2020 and the Poisons Standard (SUSMP). Therapeutic sunscreens are regulated by the Therapeutic Goods Act 1989, supported by the Therapeutic Goods Regulations 1990, and administered by the Therapeutic Goods Administration (TGA). The Therapeutic Goods (Excluded Goods) Determination 2018 excludes secondary sunscreens, whereas the Australian Regulatory Guidelines for Sunscreens (ARGS) provide regulatory guidance. The Australian/New Zealand Sunscreen Standard AS/NZS 2604:2021, mandatory for new products listed in the Australian Register of Therapeutic Goods (ARTG) since 1 July 2024, specifies performance testing and labeling requirements. In addition, the Therapeutic Goods (Permissible Ingredients) Determination (No. 2) 2024, Therapeutic Goods Order No. 92, Therapeutic Goods (Permissible Indications) Determination (No. 1) 2021, and the Therapeutic Goods Advertising Code 2021 regulate permitted ingredients, labeling, indications, and advertising, while manufacturing must comply with the PIC/S Guide to Good Manufacturing Practice (PE009-16)

• UK Cosmetic Regulation:

The Guidance on the Safety Assessment of Nanomaterials in Cosmetics specifies the information required in the safety dossier for nanomaterials. The SCCS Notes of Guidance for the Testing of Cosmetic Ingredients and Their Safety Evaluation outline the safety assessment requirements for cosmetic ingredients other than nanomaterials. In addition, the Checklists for Applicants Submitting Dossiers on Cosmetic Ingredients to be Evaluated by the SCCS provide a checklist of the information and documents required for submission of safety dossiers.

• South Korea Cosmetic Regulation:

 The Cosmetics Act provides the legal framework for the comprehensive regulation of cosmetic products. Its implementation is supported by the Enforcement Decree of the Cosmetics Act, which guides government supervision and enforcement. In addition, the Regulation on Safety Standards for Cosmetics establishes safety requirements for cosmetic ingredients and other safety management measures applicable to the manufacture, import, and distribution of cosmetic products.

• Canadian Cosmetic Regulation:

The Cosmetic Regulations (CR), established under the Food and Drugs Act, set out requirements for the notification, inspection, importation, sampling, sale, labeling, packaging, and safety of cosmetic products. The Guidelines for the Nonprescription and Cosmetic Industry Regarding Non-therapeutic Advertising and Labelling Claims help distinguish cosmetic claims from therapeutic claims and are used by Advertising Standards Canada for the preclearance of cosmetic advertising. The Classification of Products at the Cosmetic–Drug Interface provides guidance for classifying products that fall between cosmetic and drug categories.

• Guidance on Heavy Metal impurities in Cosmetics:

Many heavy metals are not acceptable as ingredients in cosmetic products sold in Canada as they may cause injury to the health of the user. Yet they may still be found in cosmetics as impurities because they are widely persistent in the natural environment. The purpose of this Guidance is to determine and communicate appropriate limits of impurities in cosmetic products, with the focus on heavy metal with known significant toxicological properties: lead, arsenic, cadmium, mercury and antimony.

COMPOSITION AND FORMULATION OF SUNSCREEN: [20],[21],[22],[23],[24],[25],[26],[27],[28],[29]

QUALITY CONTROL EVALUATION PARAMETER FOR SUNSCREEN: [30],[33],[34]

1.In vitro tests

Where EE (I) - erythemal effect spectrum; I(I)-solar intensity spectrum

2.In Vivo Test