Depigmenting action of phenylhydroquinone,an O-phenylphenol metabolite,on the skin of JY-4 black guinea-pigs

The effects of o-phenylphenol (OPP) and its metabolite, phenylhydroquinone (PHQ) on the skin of JY-4 black guinea-pigs were studied. Topical application of 1 or 5% PHQ on the black skin of the back caused marked depigmentation and hypopigmentation of the skin after 5 weeks, whereas OPP applied at the same concentrations had little effect. Depigmented skin had an increased L* (lightness) value in the CIE-L*a*b* color system. This corresponded with a decreased number of melanocytes and melanosomes in the melanocytes and keratinocytes, the disruption of melanosomes in the melanocytes, and destruction of the membranous organelles of the melanocytes. These morphological and numerical changes in epidermal melanocytes indicate that selective melanocyte toxicity occurred. Furthermore, application of PHQ to the skin of white guinea-pigs caused skin irritation, as shown by a colorimetric increase in a* value (redness) and by histological observation of inflammation. This study confirmed that OPP, which is a reported depigmenter, has little depigmenting action, while its metabolite, PHQ, is a potent depigmenter preferentially affecting melanocytes.