The degrees of UVB-induced erythema and pigmentation correlate linearly and are reduced in a parallel manner by topical anti-inflammatory agents

Abstract

To examine whether it is possible to evaluate the degree of ultraviolet B (UVB)-induced inflammation by measuring the degree of hyperpigmentation, we investigated the relationship between UVB-induced erythema and the subsequent pigmentation quantitatively. At 24 h and 7 d after irradiation with erythemogenic doses of UVB to the backs of 16 Japanese subjects, the degree of induced erythema (delta erythema index) and that of pigmentation (delta melanin index) were examined by an image analytic method using a videomicroscope interfaced with a computer. The relationship between two indices was linear in each subject, and the correlation coefficient was 0.83 when evaluated using whole data. The slope of the regression line for the delta melanin index against delta erythema index tended to become steeper as non-irradiated skin color became darker (r = 0.63), suggesting that more efficient melanogenesis takes place after the same level of inflammation in the subject with darker skin. Both erythema and hyperpigmentation were suppressed significantly and in a parallel manner by corticosteroids and indomethacin applied topically immediately after UVB irradiation. These results imply that the post-inflammatory hyperpigmentation correlates closely with the severity of the prior inflammation and that chemical mediators released in the inflammatory process have considerable influence on the melanogenesis. We conclude that the measurement of UVB-induced hyperpigmentation can be utilized for the assessment of topical anti-inflammatory agents, unless these have direct actions on the tyrosinase activity of melanocytes.