X-ray photoelectron spectroscopy (XPS) has been used to study the chemical states of the sulfur and nitrogen atoms in human epidermal skin and melanin it contained, as well as the oxidation mechanism of the disulfide bonds and sulfhydryl groups. It shows that when melanin is treated with hydrogen peroxide, the valence of the sulfor atoms changes from two to four and six while the colour changes from brownish-black to yellowish-brown.

Key words: CYSTINE, OXIDATION, SULFUR, REACTION MECHANISM, NITROGEN, SKIN, MERCAPTO GROUP, X-RAY PHOTOELECTRON SPECTROMETRY, HYDROGEN PEROXIDE, PIGMENTATION