Author(s): E. A. El-Khateeb, M. Abdallah and H. A. Al-Ahmar
Background. Recent accumulating data in the literature indicates a complex photoprotective role of the epidermis where the role of melanin as the major photoprotective mechanism has become debatable. Aim. To make a comparative assessment of the photoprotective roles played by different epidermal structures. Methods. 40 patients with vitiligo, with skin phototypes (SPTs) II to V, were enrolled in the study. Areas of skin (lesional and nonlesional) were delineated where the stratum corneum (SC) was stripped from half of each area to obtain 4 skin models: lesional, lesional stripped, nonlesional, and nonlesional stripped. After 24 h, skin models were exposed to broadband ultraviolet B (BB-UVB) irradiation, to measure the minimal erythema dose (MED) values which were used to indirectly assess the photoprotective role of each epidermal structure; melanin, viable epidermis (VE), and SC. Results. The MED values were significantly (P < 0.001) different among skin models for almost all comparisons, being highest in nonlesional skin, followed by nonlesional stripped, lesional, and lesional stripped skin, and a significant (P < 0.001) positive correlation was observed between MED and SPT. There were also significant (P < 0.001) differences in MED values calculated for epidermal structures for almost all comparisons, being highest for VE, followed by melanin, and then the SC, and a significant (P < 0.001) positive correlation was observed between MED and SPT. Conclusion. Epidermal photoprotection extends beyond melanin production and may involve several factors such as epidermal thickness, optical properties, and chromophores. Such a role was perceived to be reactive to ultraviolet radiation (UVR) and more efficient in those with higher SPTs.
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