The forms of hair appearing throughout life!
Lanugo hair is the first to be produced by the follicles. This usually un-pigmented, very fine hair grows from the foetus at around 20 weeks and it falls off approximately 36 weeks from conception, which is nearly full term. This means that infants are not usually born with the lanugo hair but sometimes it remains present, especially in premature births. This baby will ingest this lanugo hair as part of the amniotic fluid so it can be found in the meconium, a sticky green substance found in the gut that forms the babies first poo.
Lanugo has the purpose of holding the vernix caseosa on the skin. This is a white substance, often compared to cheese and primarily made up of sebum from the sebaceous glands at around 20 weeks from conception. This substance is hydrophobic, meaning it repels water, a quality that seems central to its purpose. This has led to the theory that its function is to prevent evaporative heat loss after birth. Others add that it also lubricates so as to facilitate passage through the the birth canal. Lanugo hair is not only found on the foetus and some newborns but it can also be found on patients of anorexia and bulimia nervosa as it is a sign of malnourishment.
After birth lanugo hair is replaced by vellus hair which is even finer and less noticeable than lanugo hair. It does not grow long (2-4cm), it doesn’t often have pigment and it is not associated with sebaceous glands. The name for this hair comes from the latin meaning ‘a fleece’, or ‘wool.’ This seems appropriate since its function is thermoregulation; this hair is associated with arrector pili muscles which when contracted cause the vellus hair to stand up. This holds a layer of insulating air on the body which slows down the rate of heat loss though radiation.
Eating disorders such as anorexia nervosa can also increase the vellus hair on a person as well as hormonal imbalances. For example in Cushing’s Syndrome the over production of cortisol, a steroid hormone produced by the adrenal glands, causes the over abundance of vellus hair. Vellus hair can also be found on the scalp of males with androgenic hair loss as modified testosterone (DHT) causes the terminal hair follicles to miniaturise such that vellus hair is produced instead.
Androgenic hair is body hair which is acquired as of puberty, this hair is thicker, coarser and darker than the other types. This hair, sometimes known as pubic hair starts of as vellus hair and then becomes androgenic hair which is often subcategorised with terminal hair (the hair growing from the head) though they are not quite the same. The two are differentiated by appearance and texture (androgenic is coarser and darker) and also by differences in growth cycles. Androgenic hair has a shorter anagen (growth) phase and a longer telogen (rest) phase. In terminal hair the growth phase lasts 2-7 years and the rest phase lasts 3 months whereas in androgenic hair the growth phase lasts several months and rest phase is approximately a year. This explains the difference in length between terminal and androgenic hair, the androgenic is growing for less time so does not grow long.Androgenic hair turns into terminal hair because of the elevated androgen levels during puberty, which are male sex hormones. It’s noteworthy that these also exist in females, as a precursor to female hormones (named oestrogens.) They are converted from one to the other by the enzyme aromatase, especially testosterone. It is thought that men exhibit more androgenic hair than women because they have more androgens than women.
Terminal hair is the hair that grows from the scalp, it grows the longest and is the strongest.
This is part of a recent essay submitted as part of my trichology course.
Authored by Agnes Marufu (Wadzie Claire)