How fast a man’s beard grows, for instance, is partly a function of how much he thinks about sex (because thinking about sex produces a testosterone surge).
Goldey and Van Anders disagree in their paper “Sexual Thoughts: Links to Testosterone and Cortisol in Men” (2011). They found that, “although sexual thoughts in increased sexual arousal, they did not change, testosterone or cortisol compared to control conditions” (p. 1461).
Kowal et al. (2021) found the same. “Beard length (directly measured and self-reported) was not related to testosterone levels or dominance; thus, no evidence was found to support the hypothesis that beards are honest (or dishonest) signals of the beard owners’ testosterone levels and dominance” (“Are Beards Honest Signals of Male Dominance and Testosterone?” Abstract).
Put simply, there is no relationship between testosterone levels and beard growth, nor is there a relationship between sexual thinking, and testosterone levels.
