Lanugo is a type of fine hair that grows on the bodies of human fetuses while they are developing in the womb.

These hairs disappear either by birth or shortly after when vellus hairs replace them. Vellus hairs are also naturally fine and transparent, but thicker than lanugo hairs. Vellus hairs are the hairs typically seen over much of the body in childhood.

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In this article, we examine the role of lanugo and why it might grow on adults.

What is lanugo?

Lanugo hair on back.
Lanugo hair develops on fetuses and usually dissapears before or just after birth. However, in some cases it may be present in adults, particularly in those with eating disorders.

Scientists do not fully understand the role that lanugo plays in the development of a fetus.

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Scientists do know, however, that lanugo hairs combine with a waxy substance called vernix caseosa to cover the body of a fetus.

As suggested in a 2009 paper, this combination of lanugo hairs and vernix, along with other factors, might play a role in the production of different hormones within the fetus.

Lanugo appears to play an essential role in the healthy development of a fetus. However, the appearance of lanugo on adults experiencing various diseases is a bit more mysterious.

One theory is that the appearance of lanugo hairs on an adult is a result of the body trying to insulate itself and preserve heat. Scientists think this because lanugo often appears alongside conditions that reduce the body’s ability to control its own temperature, such as anorexia nervosa.

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Causes

It is natural for babies to be covered in lanugo, especially if they were born prematurely. However, the reappearance of lanugo in adults is unnatural and a sign of various health conditions.

Lanugo and vellus hairs are similar in appearance, and it can be easy to confuse them. One way to tell whether someone is developing adult lanugo as a symptom of a health condition is to check for the growth of fine hairs in places where they did not grow before, such as on the face or hands.

Eating disorders

The growth of lanugo hair on an adult is almost always associated with the eating disorder anorexia nervosa.

A 2009 review lists the growth of lanugo-like hairs as one of the skin disorders that is nearly always present in people with severe anorexia cases.

The same review lists the growth of lanugo-like hairs as the second most common skin symptom to occur due to starvation in people experiencing anorexia.

The authors also mention that lanugo growth is especially common in younger people and appears mostly on the back, upper body, and forearms.

Cancer

Certain types of cancer or tumors may cause a person to develop lanugo-like hair, but this is rare.

A 2007 study reported that a person with prostate cancer developed lanugo-like hairs while experiencing the condition, but the hairs disappeared after treatment.

The study is far from conclusive. The authors note that the research only dealt with a single individual case, and was the first recorded incident of an association between prostate cancer and lanugo growth that they were aware of.

Older research, dating back to 1978, also reports the case of a man with lung cancer who experienced lanugo-like hair growth on his face, torso, hands, and feet.

These accounts are inconclusive and only involve individual cases. However, they do suggest that lanugo growth in adults might at times occur alongside various cancers. Overall, there are very few reports in the literature of lanugo hair growth associated with cancer.

Celiac disease

One 2006 review refers to a study that found one case of lanugo-like hair growth in a person who had celiac disease. The reviewers described it as the only case of such an association reported in the literature.

Treatment

Lanugo itself is not a medical condition but a natural biological response to certain health conditions and stages of life. As a result, it is not something that requires direct treatment.

In infants, lanugo is common and no cause for concern. Babies will naturally lose the hairs over the space of a few days or weeks following birth.

Adults who develop lanugo as a symptom of anorexia or other health conditions will lose the lanugo hairs as those conditions are successfully treated. For people experiencing anorexia, the hairs will disappear as they recover through improved nutrition.

Summary

Lanugo is a natural feature of the body during the growth of a fetus and often lasts for a short time following birth. It appears as fine, downy hair on the normally “hairless” parts of the body, including areas of the torso, arms, hands, and even face.

The role of lanugo in the development of fetuses is a bit mysterious, but it may play an important role in hormone regulation.

Shortly after birth, a child will lose their lanugo and vellus hairs will replace them. These hairs are also fine and will last throughout the person’s life.

Lanugo rarely reappears in adulthood. When it does, it is almost always due to advanced-stage eating disorders, particularly anorexia.

There is also some evidence to suggest that lanugo can appear as a side effect of other health conditions, including certain types of cancer and celiac disease. The research on these links is sparse and inconclusive, with very few cases being recorded, but it is worth keeping the possibility in mind.

Lanugo hairs in adults may be mistaken for vellus hairs, but can be identified as new, fine hairs growing in greater quantity in unexpected areas of the body.

The growth of lanugo in adults is thought to be an attempt by the body to warm itself in response to conditions that negatively affect body temperature.

As lanugo is not a health condition itself, it does not require treatment directly. Adult lanugo will naturally disappear when the condition triggering it, such as anorexia, is effectively treated.