Lanugo is very thin, soft, usually unpigmented, downy hair that is sometimes found on the body of a fetus or newborn. 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 adulthood is called terminal hair. It forms in specific areas and is

hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...

-dependent. The term is from the

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

'' lana'', meaning "wool."

Humans

Fetal development

During human development, the lanugo grows on

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal dev ...

es 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 The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products between ...

and urinates into its environment. As a result, lanugo contributes to the new-born baby's meconium. The presence of lanugo on new-borns is not necessarily a sign of

premature birth Preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 weeks, very early preterm birth is between ...

, 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 Vernix caseosa, also known as vernix or birthing custard, is the waxy white substance found coating the skin of newborn human babies. It is produced by dedicated cells and is thought to have some protective roles during fetal development and for ...

on the skin. Together they protect the delicate fetal skin from being damaged by the amniotic fluid. The vernix caseosa also helps to prepare the fetus for life outside the womb. It provides lubrication for birth and contributes to thermoregulation, prevention of water loss, and innate immunity. Without the lanugo to anchor the vernix caseosa, these functions would be compromised.

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 Anorexia nervosa, often referred to simply as anorexia, is an eating disorder characterized by low weight, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. ''Anorexia'' is a term of Gre ...

bulimia nervosa Bulimia nervosa, also known as simply bulimia, is an eating disorder characterized by binge eating followed by purging or fasting, and excessive concern with body shape and weight. The aim of this activity is to expel the body of calories eaten ...

Teratoma

It is often found in teratomas (congenital tumours).

Other mammals

Lanugo is also common on other mammals. For example, seals and elephants are often born with a covering of lanugo. Some species of fetal whales and dolphins also have lanugo.

References

External links

{{Authority control Human hair Neonatology