Lanugo

Lanugo refers to hair that grows on the body in an attempt to insulate the skin because of lack of fat. It is a type of pelage. Lanugo is very fine, and may grow densely on the body in places where significant amounts of hair does not normally grow. Lanugo occurs on fetuses as a normal part of gestation. Lanugo hair is usually shed and replaced by vellus hair at ~40 weeks of gestational age.

As the lanugo is shed from the skin, it is normal for the developing fetus to consume the hair with the fluid, since it drinks from the amniotic fluid and urinates it back into its environment. Subsequently, the lanugo contributes to the newborn baby's meconium. The presence of lanugo in newborns is a sign of premature birth.

Lanugo is also common on other animals. For example, seals and elephants  are often born with a covering of lanugo.

Lanugo is also a common symptom of serious anorexia nervosa, as the body attempts to insulate itself as body fat is lost.