Congenital forms of hypertrichosis are caused by genetic mutations, and are extremely rare, unlike acquired forms. Congenital hypertrichosis is always present at birth.

- Hypertrichosis lanuginosa

Congenital hypertrichosis lanuginosa is noticeable at birth, with the infant completely covered in thin lanugo hair. In normal circumstances, lanugo hair is shed before birth and replaced by vellus hair; however, in a person with congenital hypertrichosis lanuginosa, the lanugo hair remains after birth. The palms of the hands, soles of the feet, and mucous membranes are not affected. As the person ages, the lanugo hair may thin, leaving only limited areas of hypertrichosis.

- Generalized hypertrichosis

Congenital generalized hypertrichosis causes males to exhibit excessive facial and upper body hair, whereas women exhibit less severe asymmetrical hair distribution. The palms, soles, and mucous membranes are not affected.

- Terminal hypertrichosis

Congenital terminal hypertrichosis is characterized by the presence of fully pigmented terminal hair that covers the entire body. This condition is usually accompanied by gingival hyperplasia. This form is most responsible for the term "werewolf syndrome" because of the thick, dark hair that appears. People with this condition are sometimes performers at circuses because of their unusual appearance.

- Circumscribed hypertrichosis

Congenital circumscribed hypertrichosis is associated with the presence of thick vellus hair on the upper extremities. Circumscribed signifies this type of hypertrichosis is restricted to certain parts of the body, in this case, the extensor surfaces of the upper extremities. Hairy elbow syndrome, a type of congenital circumscribed hypertrichosis, shows excessive growth on and around the elbows. This type of hypertrichosis is present at birth, becomes more prominent during aging, and regresses at puberty.

- Localized hypertrichosis

Congenital localized hypertrichosis is a localized increase in hair density and length.

- Nevoid hypertrichosis

Nevoid hypertrichosis may be present at birth or appear later in life. It features an isolated area of excessive terminal hair and is usually not related to any other diseases.

Acquired hypertrichosis appears after birth. The multiple causes include the side effects of drugs, associations with cancer, and possible links with eating disorders. Acquired forms can usually be reduced with various treatments.

- Hypertrichosis lanuginosa

Acquired hypertrichosis lanuginosa is characterized by rapid growth of lanugo hair, particularly on the face. Hair also appears on the trunk and armpits, while palms and soles are unaffected. The excess hair is commonly referred to as malignant down. This hair is very fine and unpigmented.

- Generalized hypertrichosis

Acquired generalized hypertrichosis commonly affects the cheeks, upper lip, and chin. This form also affects the forearms and legs, but is less common in these areas. Another deformity associated with acquired generalized hypertrichosis is multiple hairs occupying the same follicle. It may also include abnormal hair growth patterns as what happens to the eyelashes in a condition known as trichiasis. Oral minoxidil treatments for hypertension are known to cause this condition. Topical minoxidil used for alopecia causes hair growth in the areas where it is applied, however this hair disappears shortly after discontinuing the use of topical minoxidil.

- Patterned hypertrichosis

Acquired patterned hypertrichosis is an increase in hair growth in a pattern formation. It is similar to acquired generalized hypertrichosis and is a sign of internal malignancy.

- Localized hypertrichosis

Acquired localized hypertrichosis is an increase in hair density and length often secondary to irritation or trauma. This form is restricted to certain areas of the body.

Important diagnoses to consider include female pattern hair loss (FPHL), chronic telogen effluvium (CTE), and alopecia areata (AA). FPHL is a non-scarring progressive miniaturization of the hair follicle with one of three different characteristic patterns. CTE is an idiopathic disease causing increased hair shedding and bi-temporal recession, usually in middle aged women. AA is an autoimmune attack of hair follicles that usually causes hair to fall out in small round patches.

Symptoms of hair loss include hair loss in patches usually in circular patterns, dandruff, skin lesions, and scarring. Alopecia areata (mild – medium level) usually shows in unusual hair loss areas e.g. eyebrows, backside of the head or above the ears where usually the male pattern baldness does not affect. In male-pattern hair loss, loss and thinning begin at the temples and the crown and either thins out or falls out. Female-pattern hair loss occurs at the frontal and parietal.

People have between 100,000 and 150,000 hairs on their head. The number of strands normally lost in a day varies, but on average is 100. In order to maintain a normal volume, hair must be replaced at the same rate at which it is lost. The first signs of hair thinning that people will often notice are more hairs than usual left in the hairbrush after brushing or in the basin after shampooing. Styling can also reveal areas of thinning, such as a wider parting or a thinning crown.

Perifollicular erythema and scarring white patches are seen on dermoscopy. On scalp biopsy, lymphocytic and granulomatous perifolliculitis with eccentric atrophy of follicular epithelia and perifollicular fibrosis are visualized.

A substantially blemished face, back and limbs could point to cystic acne. The most severe form of the condition, cystic acne arises from the same hormonal imbalances that cause hair loss, and is associated with dihydrotestosterone production. Seborrheic dermatitis, a condition in which an excessive amount of sebum is produced and builds up on the scalp (looking like an adult cradle cap) is also a symptom of hormonal imbalances, as is an excessively oily or dry scalp. Both can cause hair thinning.

Hidrotic ectodermal dysplasia 2, or Clouston syndrome (referred to as HED2 throughout this entry) is characterized by partial or total alopecia, dystrophy of the nails, hyperpigmentation of the skin (especially over the joints), and clubbing of the fingers. Sparse scalp hair and dysplastic nails are seen early in life. In infancy, scalp hair is wiry, brittle, patchy, and pale; progressive hair loss may lead to total alopecia by puberty. The nails may be milky white in early childhood; they gradually become dystrophic, thick, and distally separated from the nail bed. Palmoplantar keratoderma may develop during childhood and increases in severity with age. The clinical manifestations are highly variable even within the same family.

In humans, hair is commonly present on all the basal segments of the digits and invariably absent from all the terminal ones. On the middle segments, there is wide fluctuation with apparent familial and racial tendencies. Hair is present on the middle segment of the fingers more frequently than on the middle segment of the toes. Hair is most often found on the middle segment of the fourth finger.

Poliosis, also called poliosis circumscripta, is the decrease or absence of melanin (or colour) in head hair, eyebrows, eyelashes or any other hairy area. It is popularly known as white forelock when it affects hair right above the forehead.

This condition can cause single or, less commonly, multiple white patches on the hair. Some mistake these white patches for simple birth marks. In poliosis there is decreased or absent melanin in the hair bulbs of affected hair follicles; the melanocytes of the skin are usually not affected. Poliosis occurs in several genetic syndromes such as piebaldism, Waardenburg syndrome, neurofibromatosis type I, and tuberous sclerosis. It can also occur in conditions such as vitiligo, Vogt–Koyanagi–Harada disease, alopecia areata, sarcoidosis, and in association with neoplasms and some medications.

It can give rise to a "Mallen streak" that can be hereditary. Catherine Cookson wrote a novel and later a TV series called "The Mallen Streak", where a family had the condition. Sports presenter Dickie Davies, runner Sam Brown, and fashion expert Stacy London were famous for their respective Mallen streak.

Clinical evaluation along with identification of typical symptoms such as the eruption of papules on the apocrine glands along with a patient history report is used to diagnose the disease. Surgical removal along with a microscopic evaluation by a dermatopatholgist is the most reliable form of diagnosis.

On the shaft of the penis, Fordyce spots are more visible when the skin is stretched, and may only be noticeable during an erection.

The spots can also appear on the skin of the scrotum.

Oral Fordyce granules appear as rice-like granules, white or yellow-white in color. They are painless papules (small bumps), about 1–3 mm in greatest dimension. The most common site is along the line between the vermilion border and the oral mucosa of the upper lip, or on the buccal mucosa (inside the cheeks) in the commissural region, often bilaterally. They may also occur on the mandibular retromolar pad and tonsillar areas, but any oral surface may be involved. There is no surrounding mucosal change. Some patients will have hundreds of granules while most have only one or two.

Occasionally, several adjacent glands will coalesce into a larger cauliflower-like cluster similar to sebaceous hyperplasia of the skin. In such an instance, it may be difficult to determine whether or not to diagnose the lesion as sebaceous hyperplasia or sebaceous adenoma. The distinction may be moot because both entities have the same treatment, although the adenoma has a greater growth potential. Sebaceous carcinoma of the oral cavity has been reported, presumably arising from Fordyce granules or hyperplastic foci of sebaceous glands.

In some persons with Fordyce spots, the glands express a thick, chalky discharge when squeezed.

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.

Sebaceous glands are normal structures of the skin but may also be found ectopically in the mouth, where they are referred to as "oral Fordyce granules" or ectopic sebaceous glands.

On the foreskin they are called Tyson's glands, not to be confused with hirsuties coronae glandis.

When they appear on the penis, they are also called "penile sebaceous glands".

When seen as a streak of individual glands along the interface between the skin of the lip and the vermilion border, the terms Fox–Fordyce disease and Fordyce's condition have been used.

Piedra (also known as "Trichosporosis") is a hair disease caused by a fungus.

Types include:

- White piedra

- Black piedra

Symptoms may appear suddenly following any condition of heat, humidity, or friction. The apocrine glands (sweat glands) are the site of the Fox–Fordyce disease. Sudden appearance of raised bumps (papules) near the apocrine glands is characteristic of the disease. Papules are mostly skin colored, dome shaped, and itchy. Papules can be found at the sweat glands in addition to periareolar, inframammary and pubic areas. Hair follicles can become damaged as well and can result in hair loss in the affected area.

Acne keloidalis nuchae (also known as "Acne keloidalis", "Dermatitis papillaris capillitii", "Folliculitis keloidalis", "Folliculitis keloidis nuchae", and "Nuchal keloid acne") is a destructive scarring folliculitis that occurs almost exclusively on the occipital scalp of people of African descent, primarily men. This is mainly because men often cut their hair very low as opposed to women, allowing the hair to prick the occipital scalp and upset it. Acne keloidalis nuchae most commonly presents itself in individuals aged 13 to 25. The disease is closely related to pseudofolliculitis barbae and both occur frequently in black men in the military, where it is so common that services often have widely known protocols for management.

Pseudofolliculitis barbae (PFB), also known as barber's itch, folliculitis barbae traumatica, razor bumps, scarring pseudofolliculitis of the beard, and shave bumps, is a medical term for persistent irritation caused by shaving. Pseudofolliculitis barbae was first described in 1956.

HED2 is suspected after infancy on the basis of physical features in most affected individuals. GJB6 is the only gene known to be associated with HED2. Targeted mutation analysis for the four most common GJB6 mutations is available on a clinical basis and detects mutations in approximately 100% of affected individuals. Sequence analysis is also available on a clinical basis for those in whom none of the four known mutations is identified.

Cross–McKusick–Breen syndrome (also known as "Cross syndrome", "hypopigmentation and microphthalmia", and "oculocerebral-hypopigmentation syndrome") is an extremely rare disorder characterized by white skin, blond hair with yellow-gray metallic sheen, small eyes with cloudy corneas, jerky nystagmus, gingival fibromatosis and severe mental and physical retardation.

It was characterized in 1967.

Many conditions affect the human integumentary system—the organ system covering the entire surface of the body and composed of skin, hair, nails, and related muscle and glands. The major function of this system is as a barrier against the external environment. The skin weighs an average of four kilograms, covers an area of two square meters, and is made of three distinct layers: the epidermis, dermis, and subcutaneous tissue. The two main types of human skin are: glabrous skin, the hairless skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin. Within the latter type, the hairs occur in structures called pilosebaceous units, each with hair follicle, sebaceous gland, and associated arrector pili muscle. In the embryo, the epidermis, hair, and glands form from the ectoderm, which is chemically influenced by the underlying mesoderm that forms the dermis and subcutaneous tissues.

The epidermis is the most superficial layer of skin, a squamous epithelium with several strata: the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. Nourishment is provided to these layers by diffusion from the dermis, since the epidermis is without direct blood supply. The epidermis contains four cell types: keratinocytes, melanocytes, Langerhans cells, and Merkel cells. Of these, keratinocytes are the major component, constituting roughly 95 percent of the epidermis. This stratified squamous epithelium is maintained by cell division within the stratum basale, in which differentiating cells slowly displace outwards through the stratum spinosum to the stratum corneum, where cells are continually shed from the surface. In normal skin, the rate of production equals the rate of loss; about two weeks are needed for a cell to migrate from the basal cell layer to the top of the granular cell layer, and an additional two weeks to cross the stratum corneum.

The dermis is the layer of skin between the epidermis and subcutaneous tissue, and comprises two sections, the papillary dermis and the reticular dermis. The superficial papillary dermis with the overlying rete ridges of the epidermis, between which the two layers interact through the basement membrane zone. Structural components of the dermis are collagen, elastic fibers, and ground substance. Within these components are the pilosebaceous units, arrector pili muscles, and the eccrine and apocrine glands. The dermis contains two vascular networks that run parallel to the skin surface—one superficial and one deep plexus—which are connected by vertical communicating vessels. The function of blood vessels within the dermis is fourfold: to supply nutrition, to regulate temperature, to modulate inflammation, and to participate in wound healing.

The subcutaneous tissue is a layer of fat between the dermis and underlying fascia. This tissue may be further divided into two components, the actual fatty layer, or panniculus adiposus, and a deeper vestigial layer of muscle, the panniculus carnosus. The main cellular component of this tissue is the adipocyte, or fat cell. The structure of this tissue is composed of septal (i.e. linear strands) and lobular compartments, which differ in microscopic appearance. Functionally, the subcutaneous fat insulates the body, absorbs trauma, and serves as a reserve energy source.

Conditions of the human integumentary system constitute a broad spectrum of diseases, also known as dermatoses, as well as many nonpathologic states (like, in certain circumstances, melanonychia and racquet nails). While only a small number of skin diseases account for most visits to the physician, thousands of skin conditions have been described. Classification of these conditions often presents many nosological challenges, since underlying etiologies and pathogenetics are often not known. Therefore, most current textbooks present a classification based on location (for example, conditions of the mucous membrane), morphology (chronic blistering conditions), etiology (skin conditions resulting from physical factors), and so on. Clinically, the diagnosis of any particular skin condition is made by gathering pertinent information regarding the presenting skin lesion(s), including the location (such as arms, head, legs), symptoms (pruritus, pain), duration (acute or chronic), arrangement (solitary, generalized, annular, linear), morphology (macules, papules, vesicles), and color (red, blue, brown, black, white, yellow). Diagnosis of many conditions often also requires a skin biopsy which yields histologic information that can be correlated with the clinical presentation and any laboratory data.

Nevus depigmentosus or nevus achromicus is a loss of pigment in the skin which can be easily differentiated from vitiligo. Although age factor has not much involvement in the nevus depigmentosus but in about 19% of the cases these are noted at birth. Their size may however grow in proportion to growth of the body. The distribution is also fairly stable and are nonprogressive hypopigmented patches. The exact cause of nevus depigmentosus is still not clearly understood. A sporadic defect in the embryonic development has been suggested to be a causative factor.

It has been described as "localised albinism", though this is incorrect. Those with nevus depigmentosus may be prone to sunburn due to the lack of pigment, and the patient should use good sun protection. Sunscreen should be applied to all exposed skin, since reduced tanning of normal skin will decrease the contrast with hypopigmented skin. Most patients with nevus depigmentosus do not pursue treatment for their lesion. There is no way to repigment the skin. If, however, the lesion is of cosmetic concern, camouflage makeup is effective. If the lesion is small one could also consider excision.

These white spots result from abnormalities in the function of melanocytes which produce little pigment thereby resulting in white spots in skin.

Keratosis Pharyngis is a medical condition where keratin grows on the surface of the pharynx, that is the part of the throat at the back of the mouth. Keratin is a protein that normally occurs as the main constituent of hair and nails.

It is characterized by the presence of whitish-yellow dots on the pharyngeal wall, tonsils or lingual tonsils.

They are firmly adherent and cannot be wiped off.

The surrounding region does not show any sign or inflammation or any other constitutional signs.

The disease usually shows spontaneous regression.

One patient who was diagnosed with Keratosis Pharyngis had white spots on the base of the tongue and on the pharynx, and hurt a little when swallowing. No treatment was found to help, but the condition went away by itself eventually.

Folliculitis decalvans is an inflammation of the hair follicle that leads to bogginess or induration of involved parts of the scalp along with pustules, erosions, crusts, ulcers, and scale. It begins at a central point and spreads outward, leaving scarring, sores, and, due to the inflammation, hair loss in its wake. No permanent cure has been found for this condition. But there is promise in a regimen of dual therapy with Rifampin 300 mg twice daily and Clindamycin 300 mg twice daily. This new treatment can be used to control the condition, and tests have indicated that after 3 to 5 months long uninterrupted courses of treatment, many patients have seen limited to no recurrence.

Pseudofolliculitis barbae (PFB) is most common on the face, but it can also happen on other parts of the body where hair is shaved or plucked, especially areas where hair is curly and the skin is sensitive, such as genital shaving (more properly termed "pseudofolliculitis pubis" or PFP).

After a hair has been shaved, it begins to grow back. Curly hair tends to curl into the skin instead of straight out the follicle, leading to an inflammation reaction. PFB can make the skin look itchy and red, and in some cases, it can even look like pimples. These inflamed papules or pustules can form especially if the area becomes infected.

This is especially problematic for some men who have naturally coarse or tightly curling thick hair. Curly hair increases the likelihood of PFB by a factor of 50. If left untreated over time, this can cause keloid scarring in the beard area.

Pseudofolliculitis barbae can further be divided into two types of ingrown hairs: transfollicular and extrafollicular. The "extrafollicular" hair is a hair that has exited the follicle and reentered the skin. The "transfollicular" hair never exits the follicle, but because of its naturally curly nature curls back into the follicle causing fluid build-up and irritation.