Excessive hair growth and its various causes

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Causes of Hypertrichosis

Hypertrichosis is the term used to describe excess hair growth in any part of the body as compared to that of a normal person of the same race, age or sex excluding androgen induced growth.

Hypertrichosis is usually categorized as either generalized or localized but age of onset and the site of growth can also be a basis of classification. Each of the generalized and localized types is further sub-divided into congenital and acquired sub-types. Hypertrichosis involves lanugo, vellus and terminal hairs.

Generalized Congenital Hypertrichosis

Generalized Congenital Hypertrichosis is associated with many abnormalities and could also be a symptom of a more complex syndromatic disorder. In this condition, excessive facial or body hair is present at birth or could appear during infancy or even later at puberty. Some forms of this disorder may involve terminal hair.

The occurrence of this disorder in successive generations shows autosomal dominant inheritance. However, a case in Mexico, where an affected father passed this disorder to all his four daughters but to none to his nine sons, suggests a X-dominant inheritance.

Congenital hypertrichosis lanuginose is associated with dental abnormalities. This disorder may be inherited as an autosomal dominant trait but may also occur sporadically.

Generalized Acquired Hypertrichosis / GAH

Generalized acquired hypertrichosis (GAH) conditions are caused by drug intake and by underlying abnormalities. GAH induced by drugs is more common and needs to be separated from other forms of generalized hypertrichosis.

Drug induced GAH

Phenytoin, cyclosporine and minoxidil are the better known among the several drugs that cause significant generalized hypertrichosis.

Phenytoin induces hypertrichosis three months or so after its intake. Hypertrichosis induced by phenytoin affects women more than men and is more prominent on the extensor aspects of the limbs and less on the face and trunk.

60% of patients treated with cyclosporine develop hypertrichosis within six months. Thick pigmented hairs appear on the face, trunk and limbs.

Oral minoxidil and, to a lesser extent, topical minoxidil cause hypertrichosis after a few weeks of therapy. Face and extremities are the affected areas.

The hair growth disappears within a year on discontinuation of these drugs. Time for the condition to resolve depends on the hair cycling characteristics of the affected area.

GAH caused by underlying abnormalities

Several types of underlying pathological states also cause Generalized Acquired Hypertrichosis.

Exposure to chemicals, such as hexachlorobenzene induces hepatic porphyria and associated hypertrichosis. A Turkish epidemic produced such extremes on the face that the affected were called ‘monkey children’.

Head injuries often result in hypertrichosis. Earlier the condition was attributed to phenytoin drug intake by the patient but later hypertrichosis was found even in those with head injuries but who were not on the drug. This explains why some lose their hair and some do not after discontinuation of this drug.

Malnutrition and anorexia nervosa causes hypertrichosis on the limbs and trunks of some people. Hypertrichosis may also occur in children with celiac disease and in dieting women when carbohydrates are omitted for prolonged periods of time.

Children with primary hypothyroidism may have hypertrichosis where the back and the extensor surfaces of the limbs have a diffused hair growth.

Quite often, AIDS infection causes localized hypertrichosis, but a generalized form has also been observed. The mechanism for the development of hypertrichosis is unknown, but probably there are several contributing factors related to malnutrition, metabolic changes, immunological deregulation and drug intake.

Congenital hypertrichosis lanuginosa has also been frequently found associated with colorectal cancer and also with gall bladder, pancreas, urinary bladder, uterus and ovary malignancies.

A hypertrichosis of the terminal type is caused by the POEM syndrome and is most common on the extensor areas, malar areas and the forehead.

Localized congenital hypertrichosis

Spinal hypertrichosis shows excess hair over the spine and could be the effect of spinal or vertebral defects. Hair growing in a patch on the lower back of children called ‘faun tail’ may have similar underlying causes.

Smooth muscle hamartoma is a slightly hyperpigmented pebbly patch occurring mostly on the trunk. There is an excess of smooth muscle fibers associated with hair follicles. Histological studies show that it is associated with a kind of muscle hyperplasia.

Hypertrichosis cubiti is a condition where elbows have excess hair during childhood and is partially resolved later in life. Some say it indicates nevoid abnormality and others label it as simply exaggerated growth. Of the 22 cases reported of this condition 10 had short stature though in other cases there were adequate reasons to explain short stature.

Nevoid hypertrichosis is a symmetrical patch excessive hair growth. Its cause is believed to be a developmental defect in the absence of any other explanation.

Localized acquired hypertrichosis

Localized hypertrichosis occurs when the vellus hair is changed into terminal hair following repeated friction or trauma, pressure and dermal inflammation.

Becker’s nevus is a localized condition involving the shoulders, anterior chest or the scapular regions and is often caused by sunburn.

AIDS has reportedly been the cause of acquired localized hypertrichosis of eyelashes, eyebrows and ears.

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