It’s often said that bald men are more virile. The popular theory is that they have higher levels of the male hormone testosterone, which makes them more masculine and increases their sex drive, but they lose their hair at a younger age than average as a result. The truth, though, is a little more complex.

it is not the amount of testosterone circulating in the bloodstream that dictates baldness, it’s down to genetics. Several genes are thought to be involved, all resulting in hair follicles becoming particularly sensitive to tiny amounts of circulating testosterone.

The process still isn’t fully understood, but it involves an enzyme that converts testosterone into a substance called dihydrotesterone, which causes the hair follicles to shrink in some people, possibly by choking off their supply of blood and nutrients. As the follicle shrinks, the growing cycle gets shorter and new hairs become finer and finer until only the finest so-called vellous hairs remain on the scalp. Eventually the follicle becomes dormant and no more hair is produced. This starts on the top of the scalp and then moves down over the head in the characteristic shape of male pattern baldness. Bald men are genetically more predisposed to be more sensitive to dihydrotestosterone, but the follicles on the chin are unaffected by the hormone, which is why beards continue to grow.