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.

Congenital forms of hypertrichosis are rare. Only 50 cases of congenital hypertrichosis lanuginosa have been recorded since the Middle Ages, and fewer than 100 cases of congenital generalized hypertrichosis have been documented in scientific publications and by the media. Congenital generalized hypertrichosis is isolated to one family in Mexico. Acquired hypertrichosis and hirsutism are more common. For example, hirsutism occurs in about 10% of women between ages 18 and 45.

Danforth (1921) reported that middigital hair was present in men more often than in women. Caucasians were found to have a higher incidence of middle phalangeal hair than other ethnic groups, including Afro-Americans, American Indians, and Japanese.

Saldanha and Guinsburg (1961) studied the presence or absence of middigital hair in a white population of Sao Paulo, Brazil, including 131 males and 158 females, and compared their findings with those of previous reports. The frequencies of individuals without midphalangeal hair showed striking population differences. The range among northern Europeans varied from 20 to 30%, and among Mediterraneans, from 30 to 50%. Among Japanese, American Indians, and blacks, the figures varied between about 60% and 90%. The trait was virtually absent among Eskimos.

- Midphalangeal hairiness (%)

Midphalangeal hair, or the presence/absence of hair on the middle phalanx of the ring finger, is one of the most widely studied markers in classical genetics of human populations. Although this polymorphism was observed at other fingers as well, for this kind of research, the fourth finger of the hand has been conventionally selected.

The hair is normal in quantity and is usually silvery-blond or straw-colored. It is disorderly, it stands out from the scalp, and cannot be combed flat. The underlying structural anomaly is longitudinal grooving of the hair shaft, which appears triangular in cross section. This is caused by mutations in one of three possible genes; "PADI3", "TGM" or "TCHH3." The characteristic hair shaft anomaly can be demonstrated in asymptomatic family members by scanning electron microscopy. To be noticeable, 50% of hairs must be affected by the structural abnormality. Improvement often occurs in later childhood. An autosomal dominant mode of inheritance has been suggested though an autosomal recessive pattern with varying degrees of penetrance has also been noted. The stiffness of the uncombable hair has been reasoned to be due to the triangular form of the hair shaft in cross section. It has been suggested that the condition may result from premature keratinization of the inner root sheath.

Genetic forms of localized autosomal recessive hypotrichosis include:

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.

Woolly hair nevus (alternatively spelled "Wooly hair nevus") is a congenital condition in which hair in a circumscribed area of the scalp is kinked or woolly.

"Bamboo hair" is a rare autosomal recessive genodermatosis characterized by congenital ichthyosiform erythroderma, trichorrhexis invaginata, and atopic diathesis with failure to thrive. Chronic skin inflammation results in scaling and exfoliation, predisposing these patients to life-threatening infections, sepsis, and dehydration. The Netherton syndrome Mendelian Inheritance in Man is inherited as an autosomal recessive disorder due to mutations of both copies of the "SPINK5" gene (localized to band 5q31-32), which encodes the serine protease inhibitor LEKTI (lymphoepithelial Kazal-type-related inhibitor). LEKTI is expressed in epithelial and mucosal surfaces and in the thymus. Each "SPINK5" mutation leads to a different length of LEKTI protein, resulting in genotype/phenotype correlations in cutaneous severity, susceptibility to atopic dermatitis, growth retardation, skin infection, increased stratum corneum protease activities, and elevated kallikrein levels in the stratum corneum.

Trichorrhexis invaginata, or bamboo hair, is a hair shaft abnormality that occurs as a result of an intermittent keratinizing defect of the hair cortex. Incomplete conversion of the sulfhydryl –SH group onto S-S disulfide bonds in the protein of the cortical fibers leads to cortical softness and subsequent invagination of the fully keratinized distal hair shaft into the softer, abnormally keratinized proximal hair shaft. Intussusception of the distal hair shaft into the proximal hair shaft results in a distinctive ball-and-socket hair shaft deformity. The affected hairs are brittle and breakage is common, resulting in short hairs.

Migratory lesions of ichthyosis linearis circumflexa may be caused by a dermal influx of inflammatory cells that undergo phagocytosis and digestion by keratinocytes, resulting in disruption of keratinization.

Increased transepidermal water loss resulting from the disturbance of corneocyte barrier function in erythroderma may cause profound metabolic abnormalities and hypernatremia, particularly in neonates.

Approximately 200 cases of trichorrhexis invaginata (bamboo hair) have been reported in the literature, but the true incidence is not known. The incidence of trichorrhexis invaginata (bamboo hair) may be as high as 1 case in 50,000 population.

Girls are affected more often by trichorrhexis invaginata (bamboo hair) than boys, but is present in all races.

Uncombable hair syndrome, also known as Pili trianguli et canaliculi, Spun-glass hair, and Cheveux incoiffables, is a rare structural anomaly of the hair with a variable degree of effect. It was first reported in the early 20th century and was described in the 1970s. It becomes apparent from as little as 3 months to up to 12 years of age.

Trichorrhexis invaginata (also known as "Bamboo hair" ) is a distinctive hair shaft abnormality that may occur sporadically, either in normal hair or with other hair shaft abnormalities, or regularly as a marker for Netherton's syndrome. The primary defect appears to be abnormal keratinization of the hair shaft in the keratogenous zone, allowing for intussusception of the fully keratinized and hard distal shaft into the incompletely keratinized and soft proximal portion of the shaft.

JEB also affects the human population. Symptoms are closely related to those that are seen in horses. Blisters occur over a large portion of the body and are very susceptible to agitation. There are other symptoms associated, such as alopecia (hair loss), abnormalities of fingernails and toenails, and joint deformities.

Children born with JEB may not live past the first year of age if the condition is severe enough. Other children that have a less severe case of JEB may live a normal lifespan.

JEB has documented in Belgian drafts, American Cream Draft, Breton drafts, Comtois, and American Saddlebreds. Of these horses, 12% of Belgians and 4% of Saddlebreds are thought to carry the disorder.

Monilethrix (also referred to as beaded hair) is a rare autosomal dominant hair disease that results in short, fragile, broken hair that appears beaded. It comes from the Latin word for necklace ("monile") and the Greek word for hair ("thrix").

Monilethrix is caused by mutations affecting the genes KRTHB1 (KRT81), KRTHB3 (KRT83), or KRTHB6 (KRT86) which code for type II hair cortex keratins. The disorder is inherited in an autosomal dominant manner. This means that the defective gene(s) responsible for the disorder is located on an autosome, and only one copy of the gene is sufficient to cause the disorder, when inherited from a parent who has the disorder.

Overheating: The scaling of the skin prevents normal sweating so hot weather and/or vigorous exercise can cause problems.

Eye problems: The eyelids can be pulled down by the tightness of the skin and this can make eyelids (but usually just the lower one) very red and they are prone to drying and irritation.

Constriction bands: Very rarely children with this condition can have tight bands of skin around their fingers or toes (usually at the tips) that can prevent proper blood circulation to the area.

Hair loss: Severe scaling of the skin on the scalp can lead to patchy loss of hair, but this is rarely permanent.

This condition is an autosomal recessive genetic disorder, which means the defective gene is located on an autosome, and both parents must carry one copy of the defective gene in order to have a child born with the disorder. Carriers of a recessive gene usually do not show any signs or symptoms of the disorder.

One form of ichthyosis lamellaris (LI1) is associated with a deficiency of the enzyme keratinocyte transglutaminase.

Genes involved include:

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.

While the condition has been seen in over 60 breeds of dog (including cross breeds), certain breeds have been found to be more susceptible than others to sebaceous adenitis:

- American Akita and Akita Inu

- Standard Poodle

- Vizsla

- English Springer Spaniel

- Chow Chow

- Samoyed

- Weimaraner

- Havanese

Breeds also mentioned in scientific literature as having some susceptibility include:

- German Shepherd

- Dachshund

- Old English Sheepdog

- Lhasa Apso

- Boxer

- Collie

- Toy Poodle

- Mixed-breeds

Sebaceous adenitis has no sex-predisposition. Sebaceous adenitis also occurs in cats, rabbits and horses.

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

The condition has been recognized since the mid- to late-1950s.

Research into the genetics of LFS has been conducted at the University of California, Davis and Cornell University in the United States, the University of Queensland in Australia, and the University of Pretoria in South Africa. In November, 2009, Cornell University announced a DNA test has been developed to detect carriers of LFS. Simultaneously, the University of Pretoria also announced they had developed a DNA test. Testing is now available at Cornell, Pretoria, and Queensland, Australia.

Sebaceous adenitis in an uncommon skin disease found in some breeds of dog, and more rarely in cats, rabbits and horses. characterised by an inflammatory response against the dog's sebaceous glands (glands found in the hair follicles in the skin dermis), which can lead to the destruction of the gland. It was first described in veterinary literature in the 1980s.

Lavender foal syndrome (LFS), also called coat color dilution lethal (CCDL), is an autosomal recessive genetic disease that affects newborn foals of certain Arabian horse bloodlines. Affected LFS foals have severe neurological abnormalities, cannot stand, and require euthanasia shortly after birth. The popular name originates due to a diluted color of the foals coat, that in some cases appears to have a purple or lavender hue. However, not all foals possess the lavender coat colour, colouring can range from silver to light chestnut to a pale pink. Carrier horses have no clinical signs and DNA testing can determine if a horse carries the gene.

Beech bark disease is a disease that causes mortality and defects in beech trees in the eastern United States and Europe. In North America, the disease occurs after extensive bark invasion by the beech scale insect, "Cryptococcus fagisuga". Through a presently unknown mechanism, excessive feeding by this insect causes two different fungi ("Neonectria faginata" (previously "Nectria coccinea var. faginata") and "Neonectria ditissima" (previously "Nectria galligena")) to produce annual cankers on the bark of the tree. The continuous formation of lesions around the tree eventually girdles it, resulting in canopy death. In Europe, "N. coccinea" is the primary fungus causing the infection. Infection in European trees occurs in the same manner as it does in North American trees. Though the disease still appears in Europe, it is less serious today than it once was.

Peeling skin syndrome (also known as "Acral peeling skin syndrome," "Continual peeling skin syndrome," "Familial continual skin peeling," "Idiopathic deciduous skin," and "Keratolysis exfoliativa congenita") is an autosomal recessive disorder characterized by lifelong peeling of the stratum corneum, and may be associated with pruritus, short stature, and easily removed anagen hair.

The acral form can be associated with "TGM5".