UV PROTECTION AND EVALUATION OF EFFICACY OF SUNSCREENS 337 In case of photo-unstable sunscreens, photoprotective effi cacy gets reduced on UV expo- sure. Thereafter, LPx leads to generation of potentially toxic breakdown products that reside on skin besides the presence of sunscreen on the skin. For example, butyl me- thoxydibenzoyl methane on UV exposure undergoes cleavage and generates ROS. These toxic products also interact with other excipients present in sunscreen and with skin components and increase the thiobarbituric acid reactive species level depicts LPx (86). The question here is that what are the challenging photoreactions that lead to breakdown? Previous investigations have disclosed photodecomposition of dibenzoylmethanes into com- plex mixtures in solution, loss of an N-methyl group from N,N-dimethylaminobenzoate (87), photooxidation of dibenzoylmethanes and photodimerization of dibenzoylmeth- anes (88). Gonzalez et al. (2007) investigated photostability of seven commercial sunscreens with absorption spectrum analysis. Sunscreen product (0.5 mg/cm2) was placed between plates of silica, and the area under the curve (AUC) in the spectrum was calculated for UVA (320–400 nm), UVA1 (340–400 nm), UVA2 (320–340 nm), and UVB (290–320 nm) before (AUCbefore) and after (AUCafter) UV artifi cial exposure (UVart) (980 kJ/m2 UVA and 12 kJ/m2 of UVB) and before and after UV natural (UVnat). AUC Index (AUCI), that is, AUCI = AUCafter/AUCbefore, was 0.80, then sunscreen was considered photostable. Here, joules/cm2 = J/cm2 and kilojoules/cm2= kJ/cm2. The investigations revealed that several commercially available sunscreens are not photo- stable. Instability was noticeable in the absorption region in the UVA range. Sunscreens with TiO2 particles appeared to be more photostable. UVA absorber butyl methoxydiben- zoylmethane, which was present in three out of six sunscreens in the study, was degraded during UV exposure (89). Avobenzone is not photostable and hence encouraged the need to stabilize the formula- tion so as to improve effi cacy. After UV exposure, avobenzone molecule gets transformed into a molecule that does not absorb UVA radiation consequently, UVA protection de- creases with the time spent under the sun (88). To make it a commercially viable product, manufacturers have developed systems to stabilize avobenzone in the fi nal formulations, for example. The combination of avobenzone with octocrylene, salicylates, methylben- zylidene camphor, micronized ZnO/TiO2 (90), or Bis-ethylhexyloxyphenol methoxyphe- nyl triazine (32) makes avobenzone photostable. A combination of diethylhexyl 2,6-naphthalate, avobenzone, and oxybenzone is a constituent of various sunscreens (Table IV). Dometrizole trisiloxane is effective for mid-range UVA protection. The addi- tion of dometrizole trisiloxane to terephthalylidene dicamphor sulphonic acid improves UVA protection in a synergistic manner. Tarras-Wahlberg et al. (1999) investigated UV spectrum of some photoactive organic spe- cies common in sunscreens before and after irradiation with UVA and UVB light. Possi- ble presence of breakdown products was determined using gas chromatography mass spectrometer (103). Moyal et al. (2002) utilized diffuse refl ectance spectroscopy technique that allows mea- surement of the UVA effi cacy of sunscreen products in vivo on human volunteers. The absorption spectrum of the product is obtained by measuring the change in refl ection of the skin with and without product. The obtained absorption spectrum helps in revealing

Table IV Composition of Few Commercially Available Sunscreens Marketed by Pharmaceutical Companies Product (Brand name) Active ingredients Company SPF PA factor (UVA coverage) Ref. (website) ANSOLAR Gel cream Avobenzone, Bis-ethylhexyloxyphenol methoxyphenyl triazine, octyl triazone, octocrylene and isoamyl p Stiefel SPF 30 PA+++ (91) Ansolar Lotion Methylene bis-benzotriazolyl tetramethylbutylphenol, Octyl Methoxycinnamate, Homosalate, Octyl Triazone Stiefel SPF 60 PA+++ protection Nongreasy, Hypoallergenic, noncomedogenic, water resistant (91) Spectraban sun screen serum control gel Cyclopentasiloxane, dimethicone cross polymer Stiefel SPF 40 PA+++ (PPD 13) prevents skin darkening and helps to reduce brown spots/pigmentation, offers high protection against UVA rays, protects against photoaging (92) Spectraban sensitive cream Methylene bis-benzotriazolyl tetramethylbutylphenol, octyl methoxy cinnamate Stiefel SPF 30 PA++ water-resistant properties (91) Suncros Aqua Gel Octinoxate Ranbaxy Laboratories Ltd. SPF 26 - (93) Suncros Aqua Lotion Zinc oxide, octinoxate, avobenzone and oxybenzone Ranbaxy Laboratories Ltd. SPF 50 - (94) Sunkare Lotion Avobenzone, octinoxate, oxybenzone Unichem Laboratories Ltd. SPF 26 - (95) Sunban Lotion Octyl methoxycinnamate, oxybenzone, titanium dioxide Hh Pharmaceuticals Pvt Ltd. - (96) Photoban Avobenzone, octyl Methoxycinnamate, oxybenzone Micro Labs Ltd. SPF 30 - (97) Melagard 50 Avobenzone, octinoxate, oxybenzone, zinc oxide Nicholas Piramal India Ltd. SPF 50 - (98) JOURNAL OF COSMETIC SCIENCE 338