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Lanugo is fine, downy hair as a type of fur. It is often found in teratomas (congenital tumours).

In humans[link]

Fetal development[link]

Lanugo grows on fetuses as a normal part of gestation, but is usually shed and replaced by vellus hair at about 33 to 36 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 can be explained as a remnant of our primate ancestry: fetal monkeys also develop a coat of hair at about the same stage of development. Their hair, however, does not fall out and they are born with a fully fledged coat of hair. There is no known need for a human embryo to have this transitory coat of hair, as the womb is at normal human body temperature.^[1]

A hypothesis, according to the NHS, is that lanugo has to do with temperature regulation.^[2]

Malnutrition[link]

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.^[3]

In non-human animals[link]

Lanugo is also common on other animals. For example, seals^[4] and elephants^[5][6][7] are often born with a covering of lanugo.

Fetal whales^[8] , like humans and all other primates and monkeys, also have lanugo, a remnant of when their ancestors lived on land.

References[link]

External links[link]

Look up lanugo in Wiktionary, the free dictionary.

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