UV PROTECTION AND EVALUATION OF EFFICACY OF SUNSCREENS 323 Chemical sunscreens are usually aromatic compounds conjugated with a carbonyl group. This structure helps in prevention of skin damage due to UV rays as it allows the mole- cule to absorb high-energy UV rays and release the energy as lower-energy rays (31). Furthermore, upon exposure to UV light, most of these chemical sunscreen ingredients (except avobenzone) do not undergo signifi cant chemical changes. Para-aminobenzoic acid (PABA) is one of the initial sunscreen agents to be extensively used, however its use is associated with certain drawbacks that include the use of an alcoholic vehicle, staining of clothes etc. Its limitations have been overcome by ester derivatives, mainly padimate O or octyl dimethyl PABA. Salicylates, for example, Octisalate or octyl salicylate is a weak UVB absorber and is generally used in permutation with other UV fi lters and has a fi ne safety report. However, PABA, cinnamates, and oxybenzone may lead to contact dermatitis or photosensitivity reactions. Most of the UV absorbers used in sunscreens are photostable, which include octocrylene, Zinc oxide (ZnO), Titanium dioxide (TiO2), Tere- phthalylidene dicamphor sulfonic acid, Drometrizole trisiloxane, Bis-ethylhexyloxyphenol methoxyphenyl triazine, methylene bis-benzotriazolyl tetramethylbutylphenol, etc. (4,32). Two exceptions are avobenzone and octinoxate however, avobenzone can be stabilized by UV fi lters octocrylene and bemotrizinol. Furthermore, UV fi lter Bis-ethylhexyloxyphenol methoxyphenyl triazine improves the photostability and effi cacy of sunscreens which have avobenzone and ethylmethoxycinnamate in their formulation (32). Octocrylene is also usually used in combination with other UV absorbers to accomplish superior SPF values. Oxybenzone is well intended as a broad-spectrum absorber (UVB as well as UVA2 absorber) (4). Anthranilates are weak UVB fi lters and they absorb mainly in the UVA2 portion of the spectrum. Avobenzone is used for true broad-spectrum UV protection as it provides a better shield against UV-A range (16). Particle size of TiO2 used in sunscreens range between 10 and 30 nm. On the other hand, in the formulation of dispersion, the par- ticles form aggregates of around 100 nM (4). In case of ZnO, primary particle sizes ranges between 10 and 200 nm, whereas the grades with larger particles are used in commercial Figure 7. Role of ROS in photoaging and immunosuppression.

JOURNAL OF COSMETIC SCIENCE 324 formulation, for example, Badger broad-spectrum SPF 30 Zinc oxide Sunscreen Cream, particle size ~ 70 nm–300 nm (33). To prevent oxygen radical formation TiO2 is coated with aluminum oxide or silica (34). In recent times, many oral sunscreens have also been commercialized. These products fa- cilitate different mechanisms to prevent photodamage of skin. The majority of them own antioxidant behavior, which reload the normal antioxidant potential of the body that is lost through UV exposure after systemic loss of endogenous antioxidants. For example, a com- mon carotenoid present in tomatoes, lycopene, is a very effi cient oxygen quencher and re- duces sensitivity to UV-induced erythema (35). Photoprotective and anticarcinogenic properties of dietary fl avonoids and phenolics are endorsed for their antioxidant and anti- infl ammatory activities, for example, polyphenol-enriched natural extract from the leaves of the fern Polypodium leucotomos has shown cutaneous photoprotection after single doses (36– 40). Epigallocatechin-3-gallate is the major photoprotective polyphenolic component of green tea. Investigations have revealed that oral administration prevents UVB-induced skin tumor in mice mediated through the induction of immunoregulatory cytokine IL-12. In addition, oral administration of Green tea polyphenols (GTPs) to mice, also suggested that GTPs have a potential antiphotoaging effect (41,42). Omega-3 polyunsaturated fatty acid has been reported to decrease UVB-induced sunburn and infl ammation (43). Classifi cation Figure 8. Broader mechanism of photocarcinogenesis.