Lanugo is fine, downy hair

Hair

Hair is a filamentous biomaterial, that grows from follicles found in the dermis. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class....

 as a type of fur

Fur

Fur is a synonym for hair, used more in reference to non-human animals, usually mammals; particularly those with extensives body hair coverage. The term is sometimes used to refer to the body hair of an animal as a complete coat, also known as the "pelage". Fur is also used to refer to animal...

. It is often found in teratoma

Teratoma

A teratoma is an encapsulated tumor with tissue or organ components resembling normal derivatives of all three germ layers. There are rare occasions when not all three germ layers are identifiable...

s (congenital tumours).

Fetal development

Lanugo grows on fetus

Fetus

A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...

es as a normal part of gestation

Gestation

Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....

, but is usually shed and replaced by vellus hair at about 33 to 36 weeks of gestational age

Gestational age

Gestational age relates to the age of an embryo or fetus . There is some ambiguity in how it is defined:*In embryology, gestational age is the time elapsed since conception. This interval is also termed fertilisation 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

Amniotic fluid

Amniotic fluid or liquor amnii is the nourishing and protecting liquid contained by the amniotic sac of a pregnant woman.- Development of amniotic fluid :...

 and urinates it back into its environment. Subsequently, the lanugo contributes to the newborn baby's meconium

Meconium

Meconium is the earliest stools of an infant. Unlike later feces, meconium is composed of materials ingested during the time the infant spends in the uterus: intestinal epithelial cells, lanugo, mucus, amniotic fluid, bile, and water. Meconium is almost sterile, unlike later feces, is viscous and...

. The presence of lanugo in newborns is a sign of premature birth

Premature birth

In humans preterm birth refers to the birth of a baby of less than 37 weeks gestational age. The cause for preterm birth is in many situations elusive and unknown; many factors appear to be associated with the development of preterm birth, making the reduction of preterm birth a challenging...

.

Some theorise that this is a left over stage in human development from our more recent common primate ancestors.(needs citation) Another theory, according to the NHS, is that lanugo has to do with temperature regulation.

Malnutrition

Lanugo can be observed in malnourished patients, including those with eating disorders. When found along with other physical symptoms, lanugo can help a physician make a diagnosis of anorexia nervosa

Anorexia nervosa

Anorexia nervosa is an eating disorder characterized by refusal to maintain a healthy body weight and an obsessive fear of gaining weight. Although commonly called "anorexia", that term on its own denotes any symptomatic loss of appetite and is not strictly accurate...

.

In non-human animals

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

External links

• Photo of lanugo in a human infant, The Royal Infirmary of Edinburgh