Hypertrichosis is a rare condition that involves excessive hair growth atypical for a person’s sex, age, and ethnicity. Various forms of this condition can develop, each with unique patterns of hair growth. Because of its rarity, experts understand very little about the mechanisms behind this condition, and research is ongoing.
Hypertrichosis can develop as a congenital condition due to genetic issues or be acquired later in life. Beyond this discrepancy, experts do not fully understand the causes of hypertrichosis. Current theories state that several of the congenital forms involve the reactivation of “shut down” genes that promoted hair growth in early humans. Other types occur due to genetic mutations. The acquired forms are much more variable in their causes, due to the range of potential triggers.
Signs and Symptoms
Excessive hair growth is the characteristic symptom of each form of hypertrichosis. However, each form can have a variety of other symptoms. Some people experience tooth-related issues, including the delayed eruption of teeth. Hearing issues ranging from impairment to full deafness are also possible. Areas with excessive hair growth often have skin pigment changes, as well.
Experts recognize several congenital forms of hypertrichosis:
- Generalized hypertrichosis: hair covering the body. Affected females have a 50% chance of passing on the condition to their children; males can only pass the condition to their daughters.
- Hypertrichosis lanuginosa: Unpigmented, soft, fine lanugo hair covers much of the body after birth. This version may be inheritable or occur due to genetic mutation.
- Hypertrichosis terminalis: fully-pigmented terminal hair covers the body. Gingival hyperplasia, an overgrowth of gum tissue, is common, and the most likely cause is chromosomal changes.
- Naevoid hypertrichosis: solitary patch of terminal hair with a definite edge. This type commonly manifests as a singular bushy eyebrow. A tail-like growth at the base of the spine indicates spina bifida, as well.
Medications and Hypertrichosis
A person may acquire hypertrichosis later in life. Several common medications can trigger generalized or localized forms. These include certain anticonvulsants, immunosuppressants, vasodilators, diuretics, photosensitizers, and antibiotics. The hair is typically unpigmented vellus hair, though terminal or darker hair may also develop. Medication-induced hypertrichosis is usually reversible once a person stops taking the drug.
Several conditions have links to hypertrichosis, though it is often unclear if they are the cause. Metabolic disorders, such as anorexia, are common in people with hypertrichosis. Hyperthyroidism and other hormone imbalances are also typical. Cancer may cause acquired generalized hypertrichosis. Doctors refer to this hair growth as “malignant down,” and the mechanism behind it is unknown.
Hirsutism vs. Hypertrichosis
Hirsutism is a type of hair growth that only occurs in females and children and develops due to excessive male hormones. Because of this, the pattern of hair growth is similar to that of an adult male. Hirsutism can be congenital or acquired, and chest and back hair are most common. The excessive male hormones can cause other effects, such as a deepening voice, acne, and irregular menstrual periods. Experts commonly mistake hirsutism for hypertrichosis.
Several mechanisms can trigger hypertrichosis. In a healthy child, areas of the skin transition from growing vellus hair to terminal hair. Hypertrichosis can involve this same mechanism, but in areas that do not typically produce terminal hair. Changes in the hair cycle may also be responsible for hypertrichosis. If the anagen or growth phase extends beyond what is typical, regions of the body can have excessive hair.
Clinical diagnosis of hypertrichosis is typically straightforward due to the visible symptoms. Excessive hair growth in an area that is not typical for a person’s age, sex, or ethnicity indicates hypertrichosis. To determine the cause, a doctor may look at a patient’s medical history, test their hormone levels, or perform a variety of imaging tests to detect cancer.
Congenital forms of hypertrichosis have no cure, though they are manageable. Hair removal techniques can help achieve a more typical appearance. For hypertrichosis with terminal hair, lasers appear to be the most effective removal technique. Acquired hypertrichosis treatments target the underlying cause. Removing the triggering factor usually results in a reduction of hair growth.
Hypertrichosis is a rare condition, with the congenital forms being the least common. Fewer than 100 cases of congenital generalized hypertrichosis appear in scientific publications. Congenital hypertrichosis lanuginosa is even rarer, with only around 50 recorded cases. Acquired hypertrichosis and hirsutism are more common, with the former developing in roughly 10% of females between the ages of 18 to 45.