What Is Lanugo & What Is the Purpose of It?

By (embryologist) and (fertility counselor).
Last Update: 07/28/2014

The lanugo is a hair that covers the body of babies during pregnancy. It works as a protective later against infections, also helping to keep the fetus warm, as its skin is still very thin and lacks subcutaneous fat.

Lanugo hair is thin and silky, it grows in the head about the 13th and 16h week of gestation, covering all the body of the fetus around the 20th week.

Provided below is an index with the 3 points we are going to expand on in this article.

When does lanugo fall off?

Some babies are born with some lanugo in a specific area, especially in the back, shoulders and head, because these are the parts that take the most time to fall out, the lanugo being at times quite dark and long. Nonetheless, most of the babies loss the lanugo during the 40th week of pregnancy. The removal takes place inside the uterine cavity.

The hair is suspended in the amniotic fluid, contributing to the formation of meconium, being feasible that the baby swallowed some lanugo if it is floating in the amniotic fluid. That does not represent a major problem to be concerned about, as it will be excreted in the urine.

As stated above, the lanugo is usually removed in the latter stages of pregnancy, although it can happen once the baby is born. This can be interpreted as a sign of a pre-term delivery. However, a baby can reached its full term and be born carrying lanugo; either pre-term or not, it will fall as the baby grows and develops, being replaced by proper hair.

From then on, parents will protect their child from infections, diseases and cold through hygiene, nutrition and loving cares.

It is quite frequent to spot bald areas or total baldness while lanugo is falling down after delivery. The lanugo is very thin and constant friction speeds its loss up. That is solved quickly, as the baby will have his/her head full of shiny hair in a short period of time. The quantity and quality will exclusively depend on genetic factors.

Difference between lanugo and hair

Nevertheless, the eyebrow or eyelash hair is known as terminal hair; it is stronger, longer and thicker, it does not fall down and protects the baby from external agents, such as wind or dust.

Many women that have anorexia experience the growing of lanugo, due to its skin protective function when there is a deficit of adipose tissue.Likewise, lanugo is observed in babies that have been medicated, but it is not an issue of concern, as the lanugo disappears few days later.

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 Cristina Mestre Ferrer
Cristina Mestre Ferrer
B.Sc., M.Sc.
Bachelor's Degree in Biological Sciences, Genetics & Human Reproduction from the University of Valencia (UV). Master's Degree in Biotechnology of Human Assisted Reproduction from the UV and the Valencian Infertility Institute (IVI). Embryologist at IVI Barcelona. More information about Cristina Mestre Ferrer
Adapted into english by:
 Sandra Fernández
Sandra Fernández
B.A., M.A.
Fertility Counselor
Bachelor of Arts in Translation and Interpreting (English, Spanish, Catalan, German) from the University of Valencia (UV) and Heriot-Watt University, Riccarton Campus (Edinburgh, UK). Postgraduate Course in Legal Translation from the University of Valencia. Specialist in Medical Translation, with several years of experience in the field of Assisted Reproduction. More information about Sandra Fernández

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