Lanugo is the soft, fine hair that first grows on a fetus during pregnancy, typically appearing around 16 to 20 weeks of gestation. It covers most of the body, is unpigmented or very lightly pigmented, and serves a surprisingly important purpose: anchoring a protective waxy coating to the baby’s skin. Most babies shed lanugo before birth, but premature infants are often born with it still visible, especially on the shoulders, back, and forehead.
What Lanugo Does in the Womb
Lanugo’s main job is holding vernix caseosa in place. Vernix is the thick, white, cheese-like substance that coats a fetus and acts as a barrier between delicate skin and the amniotic fluid surrounding it. Without lanugo, vernix would simply slide off. The fine hairs increase the skin’s surface area, creating more points of contact between the vernix and the body, essentially acting as a physical anchor. This keeps the protective layer intact so it can shield the fetus from harmful substances in the amniotic environment.
Lanugo also plays a role in temperature regulation. Before a fetus develops enough body fat to retain heat on its own, lanugo provides a thin layer of insulation. Once sufficient fat stores build up in the third trimester, lanugo is no longer needed, and the fetus typically sheds it. Much of this shed hair is swallowed along with amniotic fluid, and it becomes part of meconium, the baby’s first stool after birth.
Lanugo on Newborns
Full-term babies have usually shed most or all of their lanugo by the time they’re born. When some remains, it tends to show up on the shoulders, back, ears, and forehead. It’s completely harmless and falls out on its own within the first few weeks of life. No treatment or removal is needed.
Premature infants are far more likely to be born with visible lanugo because they simply haven’t reached the stage of development where shedding would normally occur. The earlier a baby is born, the more lanugo you’ll typically see. This is one of the visual markers clinicians use when estimating gestational age at birth. As a preterm baby continues to develop outside the womb, the lanugo gradually disappears.
How Lanugo Differs From Other Body Hair
The human body produces three distinct types of hair over a lifetime, and lanugo is the first. It’s extremely fine, soft, and lacks a medulla, which is the central core structure found in thicker hair. It also has little to no pigment, making it nearly invisible on some skin tones.
After lanugo sheds, it’s replaced by vellus hair, the short, thin “peach fuzz” that covers most of your body throughout life. Vellus hair is also unmedullated but persists into adulthood. Terminal hair is the third type: the thick, coarse, pigmented hair on your scalp, eyebrows, and (after puberty) the underarms, legs, and pubic area. Terminal hair contains a medulla, giving it its characteristic strength and color. Lanugo is the finest and most fragile of the three and was never designed to last.
Lanugo in Adults With Malnutrition
Lanugo isn’t only a fetal phenomenon. It can reappear in adults and older children who are severely malnourished, most notably in people with anorexia nervosa. When the body loses too much fat to regulate its own temperature, it responds by growing lanugo as a form of emergency insulation. The fine hair typically appears on the face, arms, back, and abdomen.
This growth is the body’s attempt to compensate for the loss of its natural insulating layer. It’s one of the more visible physical signs of serious malnutrition and often prompts clinical concern. The lanugo itself isn’t dangerous, but its presence signals that the body is under significant physiological stress. Once adequate nutrition is restored and body fat returns to a level that supports normal thermoregulation, the lanugo sheds on its own.
Lanugo as a Rare Cancer Symptom
In very rare cases, sudden widespread growth of lanugo-like hair in adults can be a paraneoplastic syndrome, meaning the body produces it as an indirect response to cancer rather than from the tumor itself. This condition, called acquired hypertrichosis lanuginosa, has been documented alongside several types of malignancy, including lung cancer, bladder cancer, endometrial cancer, and certain leukemias. The fine, downy hair can appear rapidly across the face and body.
This is an uncommon presentation, but it’s medically significant because the hair growth sometimes appears before the cancer is diagnosed, making it a potential early warning sign. Unlike the lanugo seen in malnutrition, this type doesn’t resolve with nutritional changes. It requires identification and treatment of the underlying malignancy.