Progressive decrease in hair diameter in Japanese with male pattern baldness.

Fifty-six Japanese with male pattern baldness were evaluated for changes in their hair diameters over three years. The mean hair diameter significantly decreased each year. The average decrease was 1.1 microns per year. Although the percentage of vellus hair increased by 3.6% over three years, this increase rate was lower than that found in Caucasians. To precisely examine the change in hair diameter, the mean distribution of this diameter was investigated. At the beginning of the study, clear peaks were observed at 95 microns in the twenties and 45 microns in the fifties. The number of thicker hairs decreased and the high frequency peak shifted to a thinner hair diameter over 3 years. To quantify the change in the distribution of hair diameter, the percentage of hairs of more than 60 microns was examined. There was a statistically significant 5.61% decrease in the percentage of hairs with a diameter of more than 60 microns over three years. Our findings suggest that the progression of male pattern baldness in Japanese is slower than that of Caucasians and that the percentage of hairs of more than 60 microns is a sensitive index to evaluate the progression of male pattern baldness and the effects of hair growth or hair loss preventive agents.