Hundred male volunteers with mild to moderate dandruff and somewhat oily scalp, have used, in a double-blind fashion, a 1% ketoconazole shampoo or a 1% zinc pyrithione shampoo. The test shampoos were applied 2 to 3 times weekly for a total period of 6 months. Several parameters that affect the general health of hair and scalp were assessed at start, and after 1, 3 and 6 months. These parameters included the percent of hairs in anagen phase, the diameter of the hairs, sebum excretion rate at the hairline, and the number of hairs shed in the 24-hour period prior to each assessment. At the end of the study, the participants were asked to complete a questionnaire regarding the cosmetic acceptability of the test shampoos.
Forty-four ketoconazole users and forty-three zinc pyrithione users completed the 6 month study period. Analysis of the different parameters shows that the hair diameter gradually increases with chronic ketoconazole use (+8.46%) over a 6 month period, whereas the diameter shows a trend to decrease with zinc pyrithione use over the same period (-2.28%). The sebum excretion rate is reduced with ketoconazole (-6.54%) while it increases with zinc pyrithione (+8.2%) over the same period of time. The number of hair shed over a 24-hour period is reduced by 16.46% with ketoconazole and 6.02% with zinc pyrithione after 6 months. Finally, the percentage hairs in anagen phase increased by 6.4% and 8.4% respectively during the study time. Except for the percentage of hairs in anagen, which showed no difference between the two groups, all other parameters were significantly different in favor of the ketoconazole shampoo.
Both shampoos have been shown to be good anti-dandruff ingredients. Assessment of parameters than can affect the health of hair and scalp, suggests that both ingredients show distinct differences in the way they affect the scalp; indicating that ketoconazole increases hair diameter and reduces scalp oil, whereas zinc pyrithione seems to yield opposite effects. This suggests that, besides their effect on the lipophilic yeast Malassezia spp, ketoconazole and zinc pyrithione act though quite different mechanisms. An overall analysis of hair diameter changes as a function of changes in sebum excretion rate suggests that a reduction in scalp oiliness seems to result in an increased hair diameter. This suggests that, in people with oily hair, regular use of ketoconazole shampoo may result in overall hair fullness.
