Medical Content

Werewolf Syndrome: The Story of Hypertrichosis

Jan 3, 2023


Hypertrichosis, also called werewolf syndrome, is a rare condition characterized by excessive hair growth anywhere on the body and can be found in both men and women. This condition can appear at birth or develop later in life, and the abnormal hair growth may cover the face and body or be present in small patches.1

Types and Symptoms of Hypertrichosis

Hypertrichosis can be classified based on the distribution of hair growth (generalized vs. localized), age of onset (congenital vs. acquired), and type of hair (lanugo vs. vellus vs. terminal). Each type has a different etiology and clinical presentation.2 Some major types of hypertrichosis are as follows:1

  • Congenital hypertrichosis lanuginosa: A neonate is born with normal lanugo (i.e., the fine hair found on a baby). However, this soft hair does not disappear with time and instead keeps growing in various parts of the infant’s body.
  • Congenital hypertrichosis terminalis: The growth of abnormal hair begins at birth and continues thereafter; with time, long and thick hair (called terminal hair) starts to cover the face and body.
  • Nevoid hypertrichosis: In this condition, excessive hair growth occurs in a defined patch or patches.
  • Acquired hypertrichosis: This type of hypertrichosis manifests later in life. Hair can grow in patches (localized) or across the body (generalized).

In addition to abnormal hair growth, individuals with hypertrichosis may face dental problems, such as missing teeth or enlarged gums.1


All types of hypertrichosis are infrequently observed. However, congenital hypertrichosis lanuginosa is particularly rare, with only around 50 cases having been documented previously.1 Prepubertal hypertrichosis has been reported in healthy infants or children of Mediterranean or South Asian descent. While most types of hypertrichosis affect men and women equally, hypertrichosis of the auricle and nasal tip and some types of hereditary hypertrichosis show a male preponderance.2


Congenital generalized hypertrichosis can be caused by several hereditary genetic syndromes involving mutations in proteins controlling hair follicle development. Some studies suggest that exposure to drugs like minoxidil in utero could predispose infants to congenital generalized hypertrichosis. Prepubertal hypertrichosis has been linked to elevations in free and total testosterone in some patients.2

Acquired generalized hypertrichosis is usually caused by drugs; the common culprits are2:

  • Antibiotics (e.g., streptomycin)
  • Anti-inflammatory drugs (e.g., benoxaprofen and corticosteroids)
  • Vasodilators (diazoxide, minoxidil, prostaglandin E1)
  • Diuretics (acetazolamide)
  • Anticonvulsants (phenytoin)
  • Immunosuppressives (cyclosporine, mycophenolate mofetil)
  • Interferon-alpha
  • EGFR inhibitors (cetuximab, panitumumab, erlotinib, gefitinib)

However, it can also be caused by the following factors:1,2

  • Traumatic brain injury
  • Juvenile hypothyroidism
  • Juvenile dermatomyositis
  • Malnutrition
  • Cancer or advanced HIV infection
  • Porphyria cutanea tarda, a condition in which the skin shows high light sensitivity

Some possible causes of localized acquired hypertrichosis are:1,2

  • Lichen simplex, a chronic condition involving itchiness and repeated scratching of a patch of skin
  • Repetitive trauma, friction, irritation, or inflammation
  • Medical interventions, such as PUVA therapy
  • Increased vascularity, a strategy used for bodybuilding in which prominent blood vessels develop near the skin’s surface

The pathophysiology of hypertrichosis is dependent on the etiology, but the pathological mechanisms underlying increased hair growth remain to be fully elucidated.2

Differential Diagnosis

The major differential diagnosis for hypertrichosis is hirsutism. Unlike hypertrichosis, which occurs in both men and women, hirsutism refers to the growth of male-pattern terminal hairs in women at androgen-dependent sites. Elevated androgen levels are the causative factor of hirsutism and this condition is thus accompanied by other signs of androgen elevation.2


There are no cures for hypertrichosis, and its congenital forms cannot be prevented. Genetic hypertrichosis is generally a lifelong disorder, although drug-induced hypertrichosis can be managed by discontinuing the medication.

In general, the treatment of hypertrichosis involves some short-term solutions, such as:1

  • Shaving
  • Chemical epilation using depilatory creams
  • Waxing
  • Plucking
  • Hair bleaching
  • Intense pulsed light treatment

Unfortunately, these solutions are only temporary and can cause skin irritation and lesions. Long-term treatments include:1,2

  • Electrolysis: Individual hair follicles are destroyed using small electrical charges
  • Laser surgery: Special lasers, e.g., 1064 nm Nd:Yag laser, 755 nm Alexandrite laser, and diode laser, are used to remove several hairs at once


  1. Hypertrichosis (Werewolf Syndrome). [Updated 2017 April 26]. In: Healthline [Internet]. Available from:
  2. Saleh D, Yarrarapu SNS, Cook C. Hypertrichosis. [Updated 2022 Jul 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from:

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