Lanugo is very thin, soft, usually unpigmented hair that is sometimes found on the body of a fetus or infant. It is the first hair to be produced by the fetal hair follicles, and it usually appears around sixteen weeks of gestation and is abundant by week twenty. 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 is called terminal hair. It forms in specific areas and is hormone-dependent.
Humans
Fetal development
During human development, the lanugo grows on
as a normal part of
gestation, but it is usually shed and replaced by
vellus hair at about thirty-three to thirty-six weeks of gestational age. As the lanugo is shed from the skin, it is normal for the hair to be consumed by the developing fetus, since it drinks from the
amniotic fluid and urinates into its environment. As a result, lanugo contributes to the newborn baby's
meconium. The presence of lanugo on newborns is not necessarily a sign of
premature birth, as it is also seen on infants born at thirty-nine weeks of gestation (full term).
Lanugo functions as an anchor to hold the vernix caseosa on the skin. Together they protect the delicate fetal skin from being damaged by the amniotic fluid.
Malnutrition
In the absence of
fat, lanugo grows to serve as a replacement insulator, and thus can be observed in malnourished patients, including those with eating disorders. When found along with other physical symptoms, for example, lanugo can help a physician make a diagnosis of
anorexia nervosa or
bulimia nervosa.
Teratoma
It is often found in
(congenital tumours).
Other mammals
Lanugo is also common on other
Mammal. For example, seals
and elephants
[ The Hair , Paul MacKenzie, Elephant Information Repository website ][ Elephant Hair, Elephant Anatomy, Animal Corner website ] are often born with a covering of lanugo. Some species of fetal whales and dolphins also have lanugo.
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