Integrated Sun Protection Factor: A New Sun Protection Factor Based on Free Radicals Generated by UV Irradiation

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Abstract
The present work uses the initial step of the whole cascade of biological effects in the skin, the creation of free radicals by means of UVA/UVB radiation, to develop a total sun protection factor. Until now, existing in vivo indices have not been fully satisfying: SPF only reflects protection from UVB light, and persistent pigment darkening is restricted to the UVA part of the sun spectrum. The quantitative measurement of free radicals generated in human skin biopsies by means of electron spin resonance X-band spectroscopy allows to determine a new total SPF. This new sun protection index covers all UVA/UVB wavelengths taking into account their effects in the epidermis as well as the dermis. Use of skin biopsies avoids exposure of human volunteers to potentially harmful radiations. The new index is always practically equal or lower than the in vivo SPF depending on the level of a product's UVA/UVB photoprotection balance. With this, we propose to name this new protection index 'integrated sun protection factor'.