What is hypertrichosis?

Hypertrichosis is excessive hair growth over and above the normal for the age, sex and race of an individual, in contrast to hirsutism, which is excess hair growth in women following a male distribution pattern. Hypertrichosis can develop all over the body or can be isolated to small patches.

Hypertrichosis may be congenital (present at birth) or acquired (arises later in life).

Hypertrichosis is really a blanket medical term that refers to excessive body hair. It can actually be generalized, symmetrically affecting most of the torso and limbs, or localized, affecting only a small area or location. The term is, however, usually reserved to refer to very above-average amount of normal body hair that is unwanted.

Nearly all the skin of the human body – with the exception of the palms and soles of the feet – are covered with hairs or hair follicles. The density of the hairs per square centimeter, the thickness of the hairs, color of the hairs, speed of hair growth, and qualities such as kinkiness tend to vary from one part of the body to another and also from one person to another. But in hypertrichosis all of the various controllers for the regulation of that genetic information are these lacking, damaged or none existent. Furthermore, there are a few subcategories of hypertrichosis.

Congenital hypertrichosis terminalis is the variation most people associate with the condition. This version involves all over body hair growth. Interestingly this form of hypertrichosis is almost always associated with gingival hyperplasia – meaning these ‘savage and vicious’ wolf men often posses very few teeth. Furthermore persons afflicted are said to have soft, smooth and gentle voices. Naevoid hypertrichosis is an unusual form of hypertrichosis where a solitary circumscribed area of hair growth occurs. It is not usually associated with any other diseases, except if it arises as a faun-tail on the lower back, then it may indicate underlying spina bifida. Naevoid hypertrichosis can occur at birth or appear later in life and symptoms can range from hairy tufted ears, tails, a heavy unibrow or excessive beard growth in females and males alike. Finally, Congenital hypertrichosis lanuginosa is a very rare form of hypertrichosis with only about 50 cases reported worldwide since the Middle Ages.

The condition is characterized by excessive hair growth on a child at birth. Most of the body is covered with lanugo hair, which is a fine, soft and silky hair that covers the fetus and which is usually shed at around 8 months gestation and replaced with fine vellus hair. In this condition the hair continues to grow throughout life. The initial shock of a fur covered infant, however, is luckily a very rare occurrence.

The exact cause of hypertrichosis is unknown. But it is believe to be a genetic disorder that is inherited or occurs as a result of spontaneous mutation.

Types of hair involved:

To understand hypertrichosis, it is necessary to be familiar with the three types of hairs that grow on humans.

Lanugo hairs: These are long, silky and light colored hairs which normally grow on embryos in the womb and are shed anytime from the seventh month of pregnancy to the first several months after birth.

Vellus hairs: These are short non-pigmented hairs, which after birth replace the lanugo hairs on all parts of the body except the scalp and eyebrows of a baby.

Terminal hairs are coarser and thicker hairs and usually pigmented. These hair follicles cover the scalp and eyebrows and, later with the onset of puberty, start to grow in the groin and underarm areas.

Generalized hypertrichosis can involve all three types of hair while localized hypertrichosis usually involves conversion of vellus hairs into terminal hairs.