Lanugo: characteristics and functions of this type of body hair

Lanugo is a term that refers to a type of very fine body hair., 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.

Despite the fact that it is a typical structure of the gestational period of the human being, these villi can also appear as symptoms of eating disorders such as anorexia nervosa.

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

• Related article: "The 3 phases of intrauterine or prenatal development: from the zygote to the fetus"

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 the human being presents throughout his life.

Hair, an ancestral trait

The hair, itself, is a continuation of the scalp formed by a keratin fiber, sulfur-rich fibrous structural protein. This structure, so common in basically all mammals, is divided into a root and a stem. The lanugo, despite being very different from the hairs present on the head, somewhat shares this basal structure. Even so, we will describe hair as a functional unit taking as reference the "terminal hair", that is, the hair that we all present on our heads.

A high metabolic and mitotic activity occurs in the root. This ends in a bulb, which houses the dermal papilla in charge of feeding the hair. The stem, for its part, 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 inclemencies. Finally, the medulla, the innermost area, occupies 21% of the surface of the hair and is made up of rounded corneas.

Human beings have three types of hair throughout their lives.:

• The lanugo, velvety hair that is part of the development of the fetus.
• Body hair, weak in color and consistency, that develops during human infancy and covers the entire body.
• The "terminal hair", of resistant consistency and variable coloration. It is about the hair present on the head.

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

Location and function

As we have already said before, 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 union of the caseous vernix (fatty material that protects the skin of the fetus against chafing and cracking) to the skin of the developing infant. This is very important, because without 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 environment, such 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 an apparently basic structure would play such an important role in the development of the human being in its early stages?

This very special hairiness appears, approximately, in the 13th week of gestation, and as we have already said, it is the first type of hair that appears in human beings. Its appearance and development is directly linked to the expression of certain hormones.. Its growth begins around the eyebrows, nose and forehead, to later expand throughout the body. By week 20, the lanugo covers the entire body surface of the fetus.

During weeks 33-36 it begins to disappear to integrate into the amniotic fluid.. This is digested by the fetus, which is why it will later end up as part of meconium, a slimy substance composed of dead cells and stomach secretions that lines the intestine of the newborn. Speaking clearly, meconium is the first feces of the newborn, as it is expelled by the baby during the first 48 hours of life after delivery.

As strange as it may seem to us, yes, the first hairs that appear on the surface of the newborn end up being excreted in their first stool. If this meconium is not excreted by the infant after the first 48 hours after delivery (which happens in 99% of cases), it is necessary to go to the pediatrician urgently, because it is likely that something is wrong evil. It is possible that the newborn presents anatomical or neuromuscular pathologies.

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

• You may be interested in: "Perinatal psychology: what is it and what functions does it perform?"

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 we find anorexia nervosa, bulimia nervosa, various nutritional disorders or the presence of a teratoma. Next, we briefly explain these pathologies.

Anorexia and bulimia nervosa

The anorexy and the bulimia manifest in various ways on the patient's skin, these disorders generate malnutrition, psychiatric disorders and atypical muscular efforts by the continued induction of vomiting.

Although the reason for the appearance of these villi in patients with anorexia and bulimia is not clear, this could respond to protective work on 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 may be hypertension, the appearance of edema or abnormal water retention, and anemia due to a 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 can appear without apparent correlation with other pathologies. There are pictures, for example, in which this type of villi has appeared in patients who have later been diagnosed with cancer. Although the causal mechanisms are not fully known, hypertrichosis (or excessive villi appearance) seems to be correlated with the appearance of carcinomas.

conclusions

As we have been able to observe in the previous lines, lanugo is a type of very fine body hair that grows to insulate the skin due to the absence of fat. This is present in the fetuses during the development of the pregnancy, but also can occur in pathological processes such as the appearance of teratomas or nutritional disorders such as anorexia or bulimia nervosa.

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

Bibliographic references:

• Cabetas Hernandez, I. (2004). Malnutrition in Anorexia Nervosa: psychosomatic approach and multidisciplinary treatment. Hospital Nutrition, 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.