Quantitative estimation of hair growth. I. androgenetic alopecia in women: effect of minoxidil.

Quantitative growth of hair over a 40-week period is reported for eight women with androgenetic alopecia. Using a random, double-blind protocol, the women were given either a 2% minoxidil solution or a placebo of vehicle only. Hair in a permanently marked site on the fronto-parietal scalp was pulled through a 1-cm-square clear plastic template, and the outline of the template was drawn on the scalp. The hair was carefully hand clipped and collected at five eight-week intervals (one untreated and four treated), using great care to collect only hairs within the marked area. Subsequent measurements included the total weight of hair grown in the marked area, the total number of hairs, and, on a randomized 50-hair subsample, the weight, lengths, and optical diameters. Calculated quantities included average weight per hair, average length, and average optical width. The average total hair weight of minoxidil-treated subjects increased over the 32-week test period by 42.5%, compared to 1.9% for the placebo-treated subjects (average p = 0.018). Changes for the average number count were 29.9% and -2.6%, respectively (average p = 0.022). These increases, observed using an unusually small number of subjects, clearly distinguished the treated subjects from the untreated. During the same test period, the averaged quantities of weight, diameter, and length from the 50-hair subsample showed insignificant change (p usually greater than 0.5). In addition to showing a larger percentage increase than did the total number, the total weight is not only easier to obtain, but less prone to error during sampling and measurement. Therefore, we recommend that total weight from a defined area be considered as the primary quantitative estimator for hair growth.

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