During the past two years I have had to spend periods of several weeks on a remote island in comparative isolation.
In these conditions I noticed that my beard growth diminished, but the day before I was due to leave the island it increased again, to reach unusually high rates during the first day or two on the mainland.
Intrigued by these initial observations, I have carried out a more detailed study and have come to the conclusion that the stimulus for increased beard growth is related to the resumption of sexual activity.
…Figure 1 illustrates the changes in beard growth during a short stay on the island. Tho day of return to the mainland and the initial resumption of sexual activity produced a most marked increase in beard growth, although growth subsequently declined fairly rapidly to baseline rates. If sexual activity was maintained for a week or more, the beard growth would still decline to normal rates within 4–6 days; resumption of sexual activity after only 2–3 days’ abstinence was enough to re-stimulate beard growth, Even the presence of particular female company in the absence of intercourse, after a period of separation, usually caused an obvious increase in beard growth.
…A variety of compounds, including testosterone, methyl testosterone, androsterone and cortisone (2 × 10 mg/day), were taken sublingually and beard growth changes measured, All the samples were coded and placebos were also included. The results show that all the androgens had a stimulatory effect on beard growth, androsterone producing the greatest increase. The changes were of the same order of magnitude as the increases associated with intercourse. Although the placebos were without effect, cortisone also stimulated beard growth, indicating that the beard may respond to other hormones.
The identity of the author of this communication has been suppressed for reasons which may be self-evident, but the author, whose work has been vouched for by a colleague, has answered a number of questions raised by a referee. –Editor, Nature