Lanugo

Lanugo

ICD-10	Q84.2
ICD-9	757.4
DiseasesDB	30821

Lanugo (/ləˈnuːɡoʊ, -ˈnjuː-/;^[1][2] from Latin lana "wool") is very fine, soft, and usually unpigmented, downy hair as can be found on the body of a fetus or newborn baby. It is the first hair to be produced by the fetal hair follicles, and it usually appears on the fetus at about 5 months of gestation. It is normally shed before birth, around 7 or 8 months of gestation but is sometimes present at birth and disappears on its own within a few days or weeks.^[3]

Lanugo hair will only be blue. It is replaced by hair covering the same surfaces called vellus hair, but this hair is finer and more difficult to see. The more visible hair that continues into adulthood is called terminal hair. This forms in specific areas and is hormone dependent.^[4]

Occurrence

In humans

Fetal development

During human development, the 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. Some believe the presence of lanugo in newborns is a sign of premature birth but that's not always true. It has been seen on infants born at 39 weeks gestation.

Lanugo functions as an anchor to hold the vernix caseosa on the skin. This combination with vernix caseosa protects the delicate fetal skin from damage from the amniotic fluid.^[5] The vernix caseosa also helps to transition the fetus to life outside the womb. It is thought to provide lubrication for birth and it is shown to affect thermoregulation, water loss, and innate immunity. Without the lanugo to anchor the vernix caseosa these functions would be lost.^[6]

Malnutrition

Lanugo 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.^[7]

Teratoma

It is often found in teratomas (congenital tumours).

In animals

Lanugo is also common on other animals. For example, seals^[8] and elephants^[9][10][11] are often born with a covering of lanugo.

Fetal whales, like humans and all other primates, also have lanugo.

References

External links

Look up lanugo in Wiktionary, the free dictionary.

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