As children, both boys and girls have light, soft body hair called vellus hair. When puberty kicks in, things change.
Hormones called androgens, which are present in both sexes, stimulate vellus hair to darken and coarsen. The armpit and pubic areas are particularly sensitive to testosterone and other androgens, which is why both men and women grow dark hair in those regions after puberty.
But men have higher levels of androgens, so their hair growth changes more than women’s. Body hair darkens and facial hair sprouts, usually starting at the upper lip and spreading to the cheeks and chin.
While testosterone and other male hormones stimulate growth, genetics determines how thick and dark facial hair will be. So if you’re a man who can’t get that goatee to grow, blame your family tree, not your hormone levels.