Lanugo is very thin, soft, usually unpigmented, downy hair that is sometimes found on the body of a fetus or newborn baby. It is the first hair to be produced by the fetal hair follicles, and it usually appears around 16 weeks of gestation and is abundant by week 20. It is normally shed before birth, around seven or eight months of gestation, but is sometimes present at birth. It disappears on its own within a few weeks.
It is replaced by hair covering the same surfaces, which is called vellus hair. This hair is thinner and more difficult to see. The more visible hair that persists into adulthood is called terminal hair. It forms in specific areas and is hormone-dependent.