174 JOURNAL OF COSMETIC SCIENCE Figure 2. Kinetics of the buildup and decay of hair melanin radicals from human hair. a. Red hair. b. Brown hair. Arrows •' and ,• indicate light on and light off. Other conditions as in Figure 1. Eumelanin and pheomelanin respond differently to photoirradiation, and this difference is reflected in the melanins extracted from hair. Conclusions of earlier workers (31) that irradiated red hair melanin produces more oxyradicals than black hair melanin are consistent with our results using ESR spin trapping and HTA fluorescence on sepia and on melanin isolated from red and brown hair (25). These results parallel those of the present study for red and brown hair. As with oxyradical production, we also found that the intrinsic ESR signals of red and brown hair melanin respond differently to irradiation above 320 nm. However, in contrast to oxyradical production, stimulation of the in- trinsic ESR signal for red hair or melanin isolated from red hair is less than that for brown

OXYRADICALS FROM PHOTOIRRADIATED HAIR 175 10 350 400 450 500 550 Wavelength (nm) Figure 3. HTA produced from irradiated wool keratin: 0.1 g wool keratin powder in 2 mM TA phosphate buffer, pH 7.6 (phosphate buffer), irradiated for 30 min. a. No additives. b. Sodium azide added (10 mM). c. Ethanol added (! M). hair or melanin isolated from brown hair. The difference is illustrated in Figure 2 for the two types of hair. Results of previous studies indicate that oxygen consumption rates are similar for pheo- and eumelanin (32,33). This result, coupled with the results of the intrinsic ESR signals, would seem to predict greater photoinduced oxyradical production from eumelanin than from pheomelanin, in contrast to the above observation that red hair and red hair melanin give a higher overall yield of oxyradicals. Thus, while the initial rate of production of oxyradicals may be similar, or even higher, for eumelanin, the fate of these radicals must be different for the two types of melanin/hair. These apparent differences in reactivity may be explained in terms of the different structures of the two types of melanin. Brown hair contains eumelanin that is oxidized enzymatically from tyrosine. Pheomelanin formation includes the cyclization and oxidative polymerization of 5-S-