Influence of Application Amount on Sunscreen Photodegradation in in vitro Sun Protection Factor Evaluation: Proposal of A Skin-Mimicking Substrate

• Published in: Photochemistry and photobiology 2012-03, Vol.88 (2), p.475-482
• Main Authors: Miura, Yoshimasa, Hirao, Tetsuji, Hatao, Masato
• Format: Article
• Language: English
• Subjects: Biomimetic Materials - chemical synthesis; Chemical compounds; Humans; Photochemistry; Photodegradation; Photolysis - radiation effects; Polymethyl Methacrylate - chemistry; Skin; Skin - radiation effects; Skin, Artificial; Spectrum Analysis; Sun Protection Factor - standards; Sunlight; Sunscreen; Sunscreening Agents - chemistry; Sunscreening Agents - radiation effects; Ultraviolet Rays
• ISSN: 0031-8655; 1751-1097
• DOI: 10.1111/j.1751-1097.2011.01042.x

Widely used polymethylmethacrylate substrates for in vitro sun protection factor (SPF) testing of sunscreens do not mimic the rough surface structure of skin, and in addition, sample loading is less than that used in in vivo SPF testing (2.00 mg cm−2). We have developed a skin‐mimicking substrate (SMS), which has furrows and ridges on its surface, like human skin. A comparison of the photodegradation profiles of sunscreens on commercially available substrates (including SMS) at the recommended application amounts, and on SMS at various application amounts showed that the photodegradation rate of photounstable sunscreen was dependent on the application amount being higher at lower application amounts. SMS at the recommended application amount of 2.00 mg cm−2 provided in vitro SPF values that were comparable with in vivo SPF values. Our results confirm that, in order to develop a reliable in vitro SPF method, which is consistent with in vivo SPF determination, it is important to use the same application amount of sample as in the in vivo method, in order to take proper account of sunscreen photostability. We have developed a polymethylmethacrylate skin‐mimicking substrate (SMS), which has furrows and ridges on its surface, like human skin. A comparison of the photodegradation profiles of sunscreens on commercially available substrates (including SMS) at the recommended application amounts, and on SMS at various application amounts showed that the photodegradation rate of photounstable sunscreen was dependent on the application amount, being higher at lower application amounts. The recommended application amount for SMS is as high as that for in vivo measurement (2.00 mg cm−2), and SMS provided in vitro sun protection factor (SPF) values that were comparable with in vivo SPF values.