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Keywords:

  • androgenetic alopecia;
  • female;
  • follicular units;
  • hair;
  • hair follicle

Summary

Background  Hair follicles exist within follicular units (FUs). In utero the central primary hair follicles are surrounded by smaller secondary follicles. Each FU is nourished by a single arborizing arrector pili muscle that attaches circumferentially around the primary follicle with variable attachment to other follicles. Androgenetic alopecia (AA) miniaturizes susceptible scalp hair follicles in a distinctive and reproducible fashion manifesting in different patterns between men and women.

Objectives  We hypothesized that there is an additional layer to the patterning in AA, with a hierarchy of susceptibility within FUs to AA, and that the diffuse hair loss seen in women with AA is due to a reduction in the number of terminal hairs per FU rather than uniform miniaturization of entire FUs.

Methods  We compared the mean numbers of FUs and terminal hairs per FU in 4-mm scalp punch biopsies in 24 women with AA with those in 21 controls.

Results  There was no significant difference in the number of FUs; however, women with AA had 2·40 terminal hairs per FU compared with 3·38 in the control group (P = 0·0001) associated with a mean increase of 0·6 vellus hairs per FU. Complete miniaturization of all hairs within the FU was not seen.

Conclusions  Diffuse hair loss in women with AA is due to a reduction in the number of terminal hairs per FU and an increase in the number of vellus hairs. This supports the hypothesis of a hierarchy of susceptibility within FUs to AA. Further investigation is required to ascertain whether secondary and tertiary hair follicles are more susceptible than primary follicles.