UV PROTECTION AND EVALUATION OF EFFICACY OF SUNSCREENS 325 of photoprotective agents has been elucidated in Figure 10. Furthermore, properties and spectrum of various photoprotective agents are summarized in Table II. It is worth men- tioning that topical antioxidants have several advantages over oral antioxidants. The skin is exposed to UV rays directly hence undergoes oxidative stress conditions. Topical application of antioxidants leads to increased concentration of AOs in epidermis and dermis. Direct ap- plication of a target area increases reservoir concentration that may be continuously de- pleted in combating ROS. Some of the photoprotectant AOs prevent the penetration of UV rays into the skin and hence act as sunscreens (44). Furthermore, it is desirable to keep these protectants on the skin surface for the best out- comes. However, the stability of antioxidants is an important issue which needs to be Figure 9. Role of oxidative damage in photocarcinogenesis. Figure 10. Classifi cation of topical and systemic photoprotective agents.

Table II Properties and UV Spectrum of Various UV Filters Used in Sunscreen Products USAN/INCI Spectral range Maximum concentration Function Remarks Regulatory status Reference Zinc Oxide UVB, UVA1, UVA2 25% Absorbs and blocks UVA and UVB rays broad-spectrum fi lter Photo stable less likely to cause irritation, responsible for a sunscreen’s white cast FDA approved (44,45) Titanium Dioxide UVB, UVA2 25% Refl ects and blocks UVA and UVB rays, does not protect against a whole range of UVA rays Photo stable, Less likely to cause irritation, responsible for a sunscreen’s white cast FDA approved (46,47) Avobenzone/Butyl Methoxydibenzoylmethane (BMBM) UVA1 3% Absorbs full-spectrum UVA rays Very photo unstable oil-soluble tends to be unstable when there is octinoxate can be stabilized by octocrylene, 4-MBC, bis- ethylhexyloxyphenol methoxyphenyl triazine, terephthalydiene dicamphor sulfonic acid, and other UV fi lters or photostabilizers not irritating to skin microencapsulated avobenzone could minimize its degradation in sunlight FDA approved (48) Bemotrizinol/ Bis- methoxyphenyl triazine (BEMT) UVB, UVA1, UVA2 10% Absorbs UVA and UVB rays, helps in preventing photodestabilization of other actives such as avobenzone Very photo stable, oil soluble, minimal skin penetration Not approved by FDA, marketed in Europe and Australia (49, 50) Bisoctrizole/ bis-benzotriazolyl tetramethylbutyl-phenol (MBBT) UVB, UVA1, UVA2 10% Absorbs both UVA and UVB rays, refl ects and scatters some of them too, helps to stabilize other UV fi lters (e.g., octinoxate) Shows little photo degradation, dissolves poorly in both oil and water, minimally absorbed by the skin, tends to be non-irritating to skin, produced as microfi ne particles Not available in the United States (48,49) JOURNAL OF COSMETIC SCIENCE 326