Oliver–McFarlane syndrome is a condition characterized by hypertrichosis of the eyebrows and eyelashes.

The exact genetic mutation that causes congenital circumscribed, localized, and nevoid hypertrichosis is unknown.

Acquired hypertrichosis lanuginosa is commonly present with cancer. This condition is also linked to metabolic disorders, such as anorexia, hormone imbalances, such as hyperthyroidism, or as a side effect of certain drugs.

Acquired generalized hypertrichosis may be caused by cancer. The resulting hair growth is known as malignant down. The mechanism behind cancer induced hypertrichosis is unknown. Oral and topical minoxidil treatments are also known to cause acquired generalized hypertrichosis.

One known cause of hypertrichosis cubiti is Wiedemann-Steiner syndrome.

Genetic forms of localized autosomal recessive hypotrichosis include:

X-linked hypertrichosis is a hereditary disorders characterized by generalized congenital hypertrichosis.

Keppen–Lubinsky syndrome (KPLBS) is an extremely rare congenital disorder.The minimal clinical criteria for the Keppen–Lubinsky syndrome are as follows: normal growth parameters at birth, postnatal growth failure, peculiar face with an aged appearance (large prominent eyes, a narrow nasal bridge, a tented upper lip, a high palate, an open mouth), skin tightly adherent to facial bones, generalized lipodystrophy, microcephaly, and development delay. Keppen-Lubinsky syndrome is caused by mutation in the inwardly rectifying K+ channels encoded by KCNJ6 gene.

Hypertrichosis cubiti (also known as "hairy elbow syndrome") is a cutaneous condition characterized by multiple terminal hairs on both elbows in children.

Hypertrichosis simplex of the scalp is a cutaneous condition caused by defects in the corneodesmosin protein.

Medical knowledge and documentation of this disorder is poor, likely due to a combination of factors including recent discovery, low prevalence, and the more or less aesthetic nature of the effects of the skin disorder. Thus the pathophysiology of Becker's nevus remains unclear. While it is generally considered an acquired rather than congenital disorder, there exists at least one case report documenting what researchers claim is a congenital Becker's nevus with genetic association: a 16-month-old boy with a hyperpigmented lesion on his right shoulder whose father has a similar lesion on his right shoulder.

The most extensive study to date, a 1981 survey of nearly 20,000 French males aged 17 to 26, served to disprove many commonly held beliefs about the disorder. In the French study, 100 subjects were found to have Becker's nevi, revealing a prevalence of 0.52%. Nevi appeared in one half the subjects before the age of 10, and between ages 10 and 20 in the rest. In one quarter of cases sun exposure seems to have played a role, a number apparently lower than that expected by researchers. Also surprising to researchers was the low incidence (32%) of Becker's nevi above the nipples, for it had generally been believed that the upper chest and shoulder area was the predominant site of occurrence. Pigmentation was light brown in 75% of cases (note: subjects were Caucasian), and average size of the nevus was 125 cm² (19 in²).

Prepubertal hypertrichosis is a cutaneous condition characterized by increased hair growth, and is a relatively common finding in otherwise healthy infants and children, most often occurring in individuals of Mediterranean or South Asian descent.

Nevoid hypertrichosis is a cutaneous condition characterized by the growth of terminal hairs in a circumscribed area.

Sabinas brittle hair syndrome is inherited as an autosomal recessive genetic trait.

In a study by Howell et al. patients were located and studied by means of complete histories and physical examinations, analyses of serum trace metals, ceruloplasmin concentration, urine and serum amino acids, and routine metabolic urine screens. In addition, serum and urine luteinizing hormone (LH) and follicle-stimulating hormone (FSH) values were determined, and were interpreted in conjunction with total plasma estrogen, estradiol, and testosterone levels. Close examination demonstrated the scalp hairs were very brittle, coarse, wiry in texture, and broke off quite easily with mechanical trauma such as combing and brushing. Some hairs could be visualized in their follicles, which were broken off at the skin line. Most patients had accompanying hyperkeratosis (thickening of the skin) of moderate degree on exposed surfaces. Maxillary hypoplasia (midfacial retrusion) was significant in many patients. The brittle, short hair, reduced eyelashes, crowded teeth, and dull appearance created a characteristic facial appearance. Post-pubertal patients had development of secondary sexual characteristics consistent with their age, except for sparse pubic escutcheons. All cases studied demonstrated some degree of mental deficiency; I.Q.'s ranged between 50–60. A deficiency in eye–hand coordination was also noted.

Hypotrichosis ("" + "" + "") is a condition of abnormal hair patterns, predominantly loss or reduction. It occurs, most frequently, by the growth of vellus hair in areas of the body that normally produce terminal hair. Typically, the individual's hair growth is normal after birth, but shortly thereafter the hair is shed and replaced with sparse, abnormal hair growth. The new hair is typically fine, short and brittle, and may lack pigmentation. Baldness may be present by the time the subject is 25 years old.

Hypotrichosis is a common feature of Hallermann–Streiff syndrome as well as others. It can also be used to describe the lack of hair growth due to chemotherapy.

The opposite of hypotrichosis is hypertrichosis, where terminal hair (thick) grows in areas that would otherwise normally have vellus hair (thin), for example abnormally thick facial hair growth in women.

Nablus mask-like facial syndrome is a microdeletion syndrome triggered by a deletion at chromosome 8 q22.1 that causes a mask-like facial appearance in those affected.

It is characterized by a narrowing of the eyes, tight, glistening facial skin, and a flat, broad nose. Other features of the syndrome include malformed ears, unusual hair patterns on the scalp, bent fingers and toes and joint deformities in the hands and feet, unusual teeth, mild developmental delay, cryptorchidism, and a generally happy disposition. It is a rare genetic disorder by inheritance found in Palestinian people named after Nablus city in the West Bank. It is part of many new genetic disorders of newborns that is increasing exponentially in Arabs in recent years as reported by Centre for Arab Genomic Studies in Dubai.

A 1991 report documented the cases of nine patients with both Becker's nevus and malignant melanoma. Of the nine melanomas, five were in the same body area as the Becker's nevus, with only one occurring within the nevus itself. As this was apparently the first documented co-occurrence of the two diseases, there is so far no evidence of higher malignancy rates in Becker's nevi versus normal skin. Nonetheless, as with any abnormal skin growth, the nevus should be monitored regularly and any sudden changes in appearance brought to the attention of one's doctor.

Sabinas brittle hair syndrome, also called Sabinas syndrome or brittle hair-mental deficit syndrome, is an autosomal recessive congenital disorder affecting the integumentary system.

Achard–Thiers syndrome combines the features of adrenogenital syndrome and Cushing syndrome. It is also known as diabetic-bearded woman syndrome (diabète des femmes à barbe) and occurs mainly in post-menopausal women.

The disease is named for Emile Achard and Joseph Thiers.

Hairy palms and soles are both a type of cutaneous condition characterized by a hereditary hypertrichosis affecting the palms and soles. This condition is inherited in an autosomal dominant fashion.

Achard–Thiers syndrome affects mostly postmenopausal women and comprises diabetes mellitus, deep voice, hirsutism or hypertrichosis, clitoral hypertrophy and adrenal cortical hyperplasia or adenoma. Patients often also have amenorrhoea, hypertension and osteoporosis.

Cantu syndrome apparently is inherited in an autosomal dominant fashion and appears to be affected by the "ABCC9" gene

There is controversy over whether auricular hypertrichosis is a Y-linked or autosomal trait, or perhaps both (in different families). It was proposed also that this phenotype results from the interaction of two loci, one on the homologous part of the X and Y and one on the nonhomologous sequence of the Y.

Lee et al. (2004), by Y-chromosomal DNA binary-marker haplotyping, suggested that a cohort of southern Indian hairy-eared males carried Y chromosomes from many haplogroups of the Y-phylogeny. According to a hypothesis of Y linkage, it would require multiple independent mutations within a single population. No significant difference between the Y-haplogroup frequencies of hairy-eared males and those of a geographically matched control sample of unaffected males was established. They concluded that the auricular hypertrichosis is not Y-linked in southern India, but it is unlikely to be same in any population.

Gingival fibromatosis with hypertrichosis is a cutaneous condition characterized by dark terminal hairs on the peripheral face, central back, and extremities. It is a RASopathy.

Costello and Noonan syndrome are similar to CFC and their phenotypic overlap may be due to the biochemical relationship of the genes mutated in each syndrome to each other. Genes that are mutated in all three of these syndromes encode proteins that function in the MAP kinase pathway.

- Mutations that cause CFC are found in the KRAS, BRAF, MEK1 and MEK2 genes.

- Costello syndrome is caused by mutations in HRAS.

- Mutations that cause Noonan syndrome have been found in PTPN11 and SOS1.

The relative severity of CFC when compared to Noonan syndrome may reflect the position in the biochemical pathway each gene occupies.

- Shp2, the protein product of the PTPN11, appears to regulate the MAP kinase pathway at or above the level of SOS1.

- SOS1 in turn regulates the activities of RAS, RAF, MEK, ERK and p90RSK.

- SOS1 has been demonstrated to be a target of negative feedback by ERK and p90RSK.

Thus, any activating mutation downstream of SOS1 may be subject to less regulation that may mitigate the consequence of such mutations giving rise to the phenotypic differences seen between these syndromes.

Cantú syndrome (hypertrychotic osteochondrodysplasia) is a rare condition characterized by hypertrichosis, osteochondrodysplasia, and cardiomegaly. Less than 50 cases have been described in the literature; they are associated with a mutation in the "ABCC9"-gene that codes for the ABCC9-protein.