Melanin index

The results are showu as index numbers, pigmentation index also denominated melanin index, which can vary from 0 to 1000 (Edwards, 1995). The system can also be used to calculate haemoglobin index from the same experimental determinations this index is of interest to quantily the cutaneous degree of erythema (Fullerton et al, 2003) and consequently skin improvanent after using after-sun cosmetics. 

Figure 14.3 Absorption spectra of water, skin melanin, hemoglobin, and fat. Also shown is the scattering spectrum of 10% intralipid, a lipid emulsion often used to simulate tissue scattering. Data are obtained from http //omlc.ogi.edu/spectra/index.html.

The fate of radiation incident upon the skin is determined by the optical properties of the tissue. Two basic interactions with photons occur - scattering and absorption. When radiation strikes the skin, part is scattered back to the environment, part is absorbed in various layers, and part is transmitted inward until the energy has been dissipated. At the surface of the stratum corneum a fraction of about 5-7% of the incident radiation is scattered backward (reflected), since the refractive index of the stratum corneum (nsc l-55) is much higher than that of air (n = 1.00). In the epidermis, aromatic amino acids (both free and in protein, wavelength of absorption maximum Xmax near 275 nm), urocanoic acid (X av near 277 nm at pH 7.4), nucleic acids (X ax near 260 nm), and melanin (broad absorption... 

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