Oxygen radicals from photoirradiated human hair: An ESR and fluorescence study

Abstract

Exposure of hair to light causes degradation, the precise mechanism of which is not completely understood. Oxygen free radicals (superoxide and hydroxyl) are believed to be involved, and a variety of indirect evidence has supported this. However, to date, direct observation of oxyradicals from photoirradiated hair has been lacking. We have used complementary electron spin resonance and fluorescence techniques to assess oxyradical production when human hair is irradiated under UVA and visible light (λ ≥ 320 nm). ESR studies include direct observation of intrinsic melanin and keratin radicals as well as spin trapping with DMPO. The fluorescence technique is based on terephthalic acid dianion (TA) as a hydroxyl radical probe. Radical scavengers are used to compete with the probe (TA or DMPO). Our results indicate that (a) oxyradicals are produced during photoirradiation, (b) terephthalate is a convenient method to study hydroxyl production in hair, (c) radical production upon irradiation varies with hair type, and (d) the effects of radical scavengers suggest potential implications for hair care product development.