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Melanin is the naturally occurring dark brown/black polymeric pigment produced in the skin of humans. It is beyond the scope of this article to elaborate on the formation and structure of melanins; if you would like to know more, I recommend Professor Giuseppe Prota's excellent review of the current status of our knowledge on the subject.
As a polyphenol and a free radical, melanin is unique in its ability to act both as an antioxidant and free-radical neutralizer.
Melanin's distribution within the epidermis is the single most important factor protecting the skin from the chronic effects of sunlight-induced damage: aging and skin cancer. However, melanin is a very poor classical sunscreen.
Melanin as Absorber
A comparison of the UV-absorption spectra of 0.001% solutions of both melanin and octyl methoxycinnamate (OMC) clearly shows that melanin is a poor substitute for OMC for preventing erythema [ILLUSTRATION FOR FIGURE 1 OMITTED]. Its absorbance is much less in the 290 to 320 nm region of the UV spectrum where the sun protection factor (SPF) is measured. To compare product performance, we gathered monochromatic protection factors for formulations containing 1% melanin and 1% OMC, using an Optometrics SPF-290S analyzer and the method of Diffey and Robson. Again, both the raw data and extrapolated in vitro SPFs show OMC to absorb much more UV than melanin (Table 1, [ILLUSTRATION FOR FIGURE 2 OMITTED]).
With OMC, using 2-7% produces an effective sunscreen. However, unlike OMC, melanin is highly colored; a product containing as little as 1% melanin is so highly colored that it has limited marketing potential. Thus, from a practical position, the effectiveness of melanin as a classical sunscreen must be evaluated at concentration levels below 1%. At these levels, melanin exhibits little or no SPF or UVA protection.
Melanin in skin: Even highly pigmented human skin does not contain …