Clinical aspects of the immediate pigment darkening (IPD) reaction in normal individuals

In order to investigate the clinical characteristics of the immediate pigment darkening (IPD) reaction for normal healthy Caucasian individuals and its conceivable relation to age, sex, skin type and to the minimal erythema dose (MED), a standardized light testing procedure was used and 72 subjects were studied. Skin type III was the most common, being found in 78% of the individuals; skin types II and IV were less common, found in only 12.5% and 9.5% respectively. Skin type I was not observed at all. Individuals with skin type II were found to have a significantly lower mean MED than those with skin types III and IV, and the IPD threshold dose was 9.0 J/cm2 or more, which was significantly more than for skin types III and IV. The IPD reaction was absent in several individuals with skin type II under the experimental conditions used. Some differences were observed concerning the mean MED and IPD threshold doses between skin types III and IV but they were not statistically significant. Age or sex did not appear to be significantly related to the MED and IPD threshold doses observed, and, furthermore, no significant correlation, either positive or negative, was found between the MED and the IPD threshold doses when investigated for individuals with skin type III.