Effects of the Photostability of Sunscreens on the in vivo Photoprotection

Lee, Ho Seong; Kang, Nam Gyu; Kim, Tae Heung

Abstract

BACKGROUND
Solar ultraviolet (UV) radiation induces sunburn, immune suppression, and various pigmentary disorders. Sunscreens are widely used to protect those untoward effects by UV but there are reports of phototoxicity or stability problems of sunscreens after exposure to UV. OBJECTIVE: We tried to compare sunscreens with different photostability in terms of their protection against various biologic responses like sunburn, immune suppression or pigmentation. METHODS: Three different sunscreens with SPF around 30 were used; Sunscreen-A (Sc-A) was photochemically inert, sunscreen-B (Sc-B) showed intermediate level of photostability, and sunscreen-C (Sc-C) was the least stable. To observe their in vivo effects, we measured sunscreen-protection against sunburn by back-skin swelling and sunburn cell formation, against immune suppression measured by depletion of Langerhans cells, local and systemic suppression of contact hypersensitivity (CHS), and against pigmentation by irradiation with mixed light source with UVA and UVB lamps that mimic solar UV spectrum. RESULTS: Back skin swellings by 5 kJ/m2 of UVB were protected well by sunscreens, but protection of Sc-C against 50 kJ/m2 of UVB was worse than Sc-A or Sc-B. Sunburn cells were increased significantly in mice irradiated with 5 kJ/m2 of UVB and it was protected by sunscreens, and the effect of photostability was minimal. Depletion of epidermal Langerhans cells by 5 kJ/m2 of UVB was protected completely by sunscreens. Local suppression of CHS by 5 kJ/m2 of UVB was protected by sunscreens, and Sc-A had better protection. But, in the experiment with 50 kJ/m2 of UVB, the protective efficacy was reversed; Sc-A showed worse protection. Systemic suppression of CHS by 10 kJ/m2 of UVB was protected well by sunscreens, and Sc-A had better protection and Sc-C had worse protection. In the experiment irradiated with 100 kJ/m2 of UVB, the protection of sunscreens was decreased, and Sc-B showed better protection, whereas Sc-C showed worse protection. In UV-induced pigmentation, all three sunscreens showed significant protection both by L* value and individual topographic angle (ITA) with the best protection by Sc-A and the worst protection by Sc-B. CONCLUSION: These data showed sunscreens can protect various in vivo responses and photostability of sunscreens played important roles particularly in the back-skin swelling and systemic suppression of CHS by high dose of UVB.