» For the wasp genus, see Lanugo (wasp) Lanugo is 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 doesn't normally grow. It occurs on fetuses as a normal part of gestation, but is usually shed and replaced by vellus hair at about 40 weeks of gestational age. As the lanugo is shed from the skin, it's normal for the developing fetus to c… (More on Lanugo)