Lanugo hair, which is fine, delicate, and downy, emerges to cover a fetus. This type of hair typically emerges during the fourth or fifth month of pregnancy and tends to vanish by the ninth month. In certain cases, lanugo hair might still be present in premature infants.
Lanugo hair can resurface in adults who are dealing with cancer. It may also manifest in individuals experiencing the eating disorder anorexia nervosa, or as a potential side effect of specific medications, particularly ciclosporin.