Lanugo: characteristics and functions of this type of body hair

Lanugo is the first body hair that grows on us. Let's see what it looks like and what it is used for.

Lanugo is a term that refers to a very fine type of body hair, which grows as a skin insulator in response to the skin.which grows as a skin insulator in response to the absence of fat. It occurs in humans during fetal development, but is also present in other mammals.

Although it is a typical structure of the human gestational period, these villi can also appear as a symptom of eating disorders such as anorexia nervosa.

If you want to know more about this type of hair so linked to the first stages of human life, we encourage you to continue reading.

Lanugo: fetal hairiness

Before going fully into the functionality of these very specific structures, it is necessary to clarify what hair is in general and what are the types that humans present throughout their lives.

Hair, an ancestral feature

Hair itself is a continuation of the scalp made up of a keratin fiber, a fibrous structural protein rich in sulfur.a fibrous structural protein rich in sulfur. This structure, so common in basically all mammals, is divided into root and shaft. Lanugo, although very different from the hairs present on the head, shares this basal structure to some extent. Even so, we will describe the hair as a functional unit taking as a reference the "terminal hair", that is, the hair we all have on our head.

High metabolic and mitotic activity takes place at the root. This ends in a bulb, which houses the dermal papilla responsible for nourishing the hair. The shaft is the main section of the hair and is divided into three different zones: cuticle, cortex and medulla, in order of depth.

The cortex, the intermediate zone, occupies 70% of the hair and gives it its characteristic mechanical properties. The cuticle, on the other hand, represents 9% of the hair shaft and is responsible for protecting it from environmental influences. Finally, the medulla, the innermost zone, occupies 21% of the hair surface and is composed of rounded corneas.

Humans have three types of hair throughout their lives:

• Lanugo, velvety hair that is part of the development of the fetus.
• Body hair, of weak color and consistency, which develops during infancy and occupies the entire body.
• The "terminal hair", of resistant consistency and variable coloration. This is the hair present on the head.

As we can see, the world of hair harbors more secrets than you might at first think. If you want to know more about lanugo, we encourage you to continue with the following lines.

Location and function

As mentioned above, lanugo is a type of fine hair that is present in fetuses, newborns and people with certain nutritional disorders.

This type of structure plays an essential role in the attachment of the vernix caseosa (a fatty material that protects the skin of the fetus from chafing and cracking) to the skin of the developing infant.. This is very important, because without the vernix caseosa, the baby's skin would wrinkle excessively due to constant exposure to amniotic fluid.

In addition to this integral function, the lanugo protects the fetus from harmful substances present in the maternal environmentsuch as urea and electrolytes. It also prevents water loss, promotes the innate immunity of the fetus and plays an essential role in thermoregulation. Who would have thought that such a seemingly basic structure would play such an important role in the development of early human beings?

This very special hair appears at approximately the 13th week of gestation and, as we have already mentioned, it is the first type of hair to appear in humans. Its appearance and development is directly linked to the expression of certain hormones.. Its growth begins around the eyebrows, nose and forehead, and later expands all over the body. Around week 20, lanugo covers the entire body surface of the fetus.

During the 33-36 weeks, it begins to disappear and becomes part of the amniotic fluid.. This is digested by the fetus, so it will later become part of meconium, a viscous substance composed of dead cells and stomach secretions that line the newborn's intestine. Clearly speaking, meconium is the first feces of the newborn, since it is expelled by the baby during the first 48 hours of life after birth.

Strange as it may seem, yes, the first hairs that appear on the surface of the newborn are eventually excreted in its first bowel movement. If this meconium is not excreted by the infant after the first 48 hours after birth (which happens in 99% of the cases), it is necessary to visit the pediatrician urgently, as it is likely that something is wrong. The newborn may have anatomical or neuromuscular pathologies.

Lanugo is still present in 30% of newborns.. This is a normal occurrence that certainly does not need to alert the parents. However, if it is present at the birth of the baby, it falls off by itself after the first weeks of delivery, leaving room for the body hair and terminal hairs that we have already described above.

Lanugo and diseases

As we have already said in previous lines, the presence of lanugo in an adult individual is a symptom of a serious pathology. Among the diseases that produce the appearance of these villi are anorexia nervosa, bulimia nervosa, various nutritional disorders or the presence of a teratoma. These pathologies are briefly explained below.

Anorexia and bulimia nervosa

Anorexia and bulimia manifest themselves in different ways on the patient's skin, since these disorders generate malnutrition, psychiatric disturbances and atypical muscular efforts due to the by the continuous induction of vomiting.

Although the reason for the appearance of these villi in patients with anorexia and bulimia is not clear, it could respond to a protective function of the skin due to the absence of fat.

Of course, the appearance of these villi is not the most serious consequence of these eating disorders. Other effects can be hypertension, the appearance of edema or abnormal water retention and anemia due to the lack of iron and protein intake. Emotional symptoms such as depression, sleep disorders and abandonment of normal activities also appear. For all these reasons, both medical and psychological approaches are essential in the treatment of this pathology.

Teratoma

Teratomas are encapsulated tumors with tissue or organ components reminiscent of the "normal" structures of the three germ layers that make them up. Lanugo usually appears in these congenital tumors.

Other specific cases have been detected in which lanugo may appear without apparent correlation with other pathologies. There are cases, for example, in which this type of hair has appeared in patients who were later diagnosed with cancerous processes. Although the causal mechanisms are not fully understood, hypertrichosis (or excessive hairiness) seems to be correlated with the appearance of carcinomas.

Conclusions

As we have seen in the previous lines, lanugo is a type of very fine body hair that grows as an insulator of the skin due to the absence of fat. It is present in fetuses during the development of pregnancy, but it is also present in the fetus. may occur in pathological processes such as the appearance of teratomas or nutritional disorders such as anorexia or bulimia nervosa.

Although characteristic of humans, this type of hairiness is also present in other mammals. is also present in other mammals, such as sealssuch as seals, elephants or deer during fetal development. Despite its anecdotal nature and the lack of knowledge of these structures by the general population, we can affirm that the lanugo is an essential structure for the correct development of the neonate.

Bibliographic references:

• Cabetas Hernández, I. (2004). Malnutrition in Anorexia Nervosa: psychosomatic approach and multidisciplinary treatment. Nutrición Hospitalaria, 19(4), 225-228.
• Changhong, S., & Wei, Z. (2007). Relationship between structure and function of lanugo in roe deer. JOURNAL-NORTHEAST FORESTRY UNIVERSITY-CHINESE EDITION-, 35(3), 68.
• Gworys, B., & Domagala, Z. (2003). The typology of the human fetal lanugo on the thorax. Annals of Anatomy-Anatomischer Anzeiger, 185(4), 383-386.
• Mar, B. (2008). A woman with acquired, diffuse, lanugo-like hair growth. The Medical Journal of Australia, 188(9), 536-536.
• Strumia, R. (2009). Skin signs in anorexia nervosa. Dermato-endocrinology, 1(5), 268-270.
• Verhave, B. L., & Lappin, S. L. (2018). Embryology, Lanugo.