The difference is in the hair each follicle makes
A hair follicle is a tiny pocket in the skin that produces a hair shaft. Many follicles across the human body make vellus hair: short, fine, lightly pigmented strands that are easy to miss. Chimpanzee body hair is generally longer, thicker, and more visible, so a similar number of follicles can create a much fuller-looking coat.
Follicle count alone does not determine how hairy someone—or another primate—looks. The diameter and color of each strand, how long it grows, and where it appears all affect whether it stands out. Human follicles on the scalp, for example, produce conspicuous hair, while many on the arms and torso produce barely noticeable fuzz.
From visible coat to fine body hair
The contrast is often described as humans having lost most of their body hair, but the follicles did not simply vanish. Across much of the body, hair became finer and less conspicuous. Some follicles still produce thicker terminal hairs, including those on the scalp and, after puberty, in areas such as the underarms and face.
That distinction also explains why shaving does not make hair grow back thicker: cutting a strand changes its blunt tip, not the follicle beneath the skin. The surprising part is that a comparatively bare-looking body can still be densely equipped with hair-producing structures; what changed most is what those structures produce.
