Eosinophilic folliculitis associated with HIV infection typically affects individuals with advanced HIV and low T helper cell counts. It affects both men and women as well as children with HIV and is found throughout the world.

EF may also affect individuals with hematologic disease such as leukemia and lymphoma. It may also affect otherwise normal infants in a self-limited form. HIV-negative individuals can also develop EF — this is more common in Japan.

The cause of EF is unknown. A variety of microorganisms have been implicated, including the mite Demodex, the yeast Pityrosporum, and bacteria. An autoimmune process has also been investigated.

Parasitic infestations, stings, and bites in humans are caused by several groups of organisms belonging to the following phyla: Annelida, Arthropoda, Bryozoa, Chordata, Cnidaria, Cyanobacteria, Echinodermata, Nemathelminthes, Platyhelminthes, and Protozoa.

Eosinophilic pustular folliculitis of infancy (also known as "Eosinophilic pustular folliculitis in infancy," "Infantile eosinophilic pustular folliculitis," and "Neonatal eosinophilic pustular folliculitis") is a cutaneous condition characterized by recurrent pruritic crops of follicular vesiculopustular lesions.

Virus-related cutaneous conditions are caused by two main groups of viruses–DNA and RNA types–both of which are obligatory intracellular parasites.

Eosinophilic cellulitis is of unknown cause. It is suspected to be an autoimmune disorder. It may be triggered by bites from insects such as spiders, fleas, or ticks, or from medications or surgery.

The exact cause of Majocchi's granuloma is not well established however a dysfunctinoal immune system may be a causative factor. The first form of MG, the superficial perifollicular form occurs predominately on the legs of otherwise healthy young women who repeatedly shave their legs and develop hair follicle occlusions that directly or indirectly disrupt the follicle and allow for passive introduction of the organism into the dermis. Hence, the physical barrier of the skin is important because it prevents the penetration of microorganisms. Physical factors that play a major role in inhibiting dermal invasion include the interaction among keratin production, the rate of epidermal turnover, the degree of hydration and lipid composition of the stratum corneum, CO levels, and the presence or absence of hair. Keratin and/or necrotic material can also be introduced into the dermis with an infectious organism to further enhance the problem. In immunocompromised individuals, the use of topical corticosteroids may lead to a dermatophyte infection due to local immunosuppression.

Eosinophilic cellulitis, also known as Wells' syndrome, is a skin disease that presents with painful, red, raised, and warm patches of skin. The rash comes on suddenly, lasts for a few weeks, and often repeatedly comes back. Scar formation does not typically occur.

Eosinophilic cellulitis is of unknown cause. It is suspected to be an autoimmune disorder. It may be triggered by bites from insects such as spiders, fleas, or ticks, or from medications or surgery. Diagnosis is made after other potential cases are ruled out. Skin biopsy of the affected areas may show an increased number of eosinophils. Other conditions that may appear similar include cellulitis, contact dermatitis, and severe allergic reactions such as anaphylaxis.

Treatment is often with a corticosteroids. Steroids applied as a cream is generally recommended over the use of steroids by mouth. Antihistamines may be used to help with itchiness. Many times the condition goes away after a few weeks without treatment. The condition is uncommon with about 200 described cases. It affects both sexes with the same frequency. It was first described by George Crichton Wells in 1971.

Urticarial dermatoses are distinct from urticaria, which examples being drug-induced urticaria, eosinophilic cellulitis and bullous pemphigoid. It is important to distinguish urticaria from urticarial dermatoses. The individual wheals of urticaria are ‘here today and gone tomorrow’ (i.e. they last less than 24 hours), whereas with urticarial dermatoses, the individual lesions last for days or longer.

Although the exact cause of feline acne is unknown, some causes include:

- Hyperactive sebaceous glands

- Poor hygiene

- Stress

- Developing secondary to fungal, viral, and bacterial infections

- Reaction to medication

- Drinking from plastic containers to which the cat is allergic

- Demodicosis or mange, causing itchiness and hair loss

- Suppressed immune system

- Hair follicles that don't function properly

- Rubbing the chin (to display affection or mark territory) on non-sanitized household items

- Hormonal imbalance

- Contracting the infection from other cats in the same household

Aside from the mosquito allergy cat, cats with EGC usually have allergy, ectoparasite infestation or possibly ringworm or other skin infection. Other implicated causes include traumatic damage, autoimmune disease or FeLV infection.

Irritant folliculitis is a cutaneous condition and usually occurs following the application of topical medications.

Most carbuncles, boils, and other cases of folliculitis develop from "Staphylococcus aureus".

Folliculitis starts with the introduction of a skin pathogen to a hair follicle. Hair follicles can also be damaged by friction from clothing, an insect bite, blockage of the follicle, shaving, or braids too tight and too close to the scalp. The damaged follicles are then infected by "Staphylococcus". Folliculitis can affect people of all ages.

Iron deficiency anemia is sometimes associated with chronic cases.

Eosinophilic granuloma is a form of Langerhans cell histiocytosis. It is a condition of both human and veterinary pathology. Colloquially, the reaction pattern is sometimes referred to as a rodent ulcer.

Feline eosinophilic granuloma complex is synonymous with "feline eosinophilic skin diseases". This is considered to be a cutaneous reaction pattern that can be the manifestation of a number of underlying infections, allergies or ectoparasite infestations. It can also be idiopathic, that is have no known underlying trigger. The eosinophilic reaction is common in feline inflammatory disease and the eosinophilic granuloma can be a hereditary reaction pattern in some lines of domestic cats.

Folliculitis is the infection and inflammation of one or more hair follicles. The condition may occur anywhere on the skin except the palms of the hands and soles of the feet. The rash may appear as pimples that come to white tips on the face, chest, back, arms, legs, buttocks, and head.

Fiddler’s neck does not usually form unless the musician is practicing or playing for more than a few hours each day, and only seems to develop after a few years of serious playing. Thus, when not infected or otherwise problematic, fiddler’s neck may be known as a benign practice mark and may be worn proudly as an indication of long hours of practice. Blum & Ritter (1990) found that 62% of 523 professional violinists and violists in West Germany experienced fiddler’s neck, with the percentage among violists being higher (67%) than among violinists (59%). Viola players are believed to be more predisposed to developing fiddler’s neck than violinists because the viola is larger and heavier, but this has not been empirically confirmed.

The development of fiddler’s neck does not depend on preexisting skin problems, and Blum & Ritter find that only 23% of men and 14% of women in their study reported cutaneous disorders in other parts of the face (mainly acne and eczema) that were independent of playing the violin or viola. Fiddler’s neck may exacerbate existing acne, but acne may also be limited solely to the lesion and not appear elsewhere. Nonetheless, musicians with underlying dermatologic diseases like acne and eczema are more endangered by fiddler’s neck than others. Males may develop folliculitis or boils due to involvement of beard hair.

There is no certainty about the cause of this disorder, but it is known that the bacterium Staphylococcus aureus has a central role. This bacterium can be detected in the lesions of most patients. It is unclear if a primarily sterile infection with secondary colonization by Staphylococcus aureus is present, or if this bactery itself leads at first to a strong immune reaction. Another possibility is that the toxins produced by this bacterium could act as superantigens that activate directly the T-cells over the variable domain of T-cell receptors. Nonetheless "Staphylococcus aureus" can by found in almost all patients affected by this disorder, while it is only seen in 20–30% of non-affected people.

As Staphylococcus aureus is not always found in people that suffer from folliculitis decalvans, other factors must be present. Through examinations in families it was found that there is a family connection to the occurrences, which leads to the conclusion that there is a genetic predisposition for it; for example, patients with folliculitis decalvans could have a hereditary different opening of the hair follicle that could facilitate the lodging of the bacteria. Immunologically, another possibility is that specially strong intercellular fixation protein ICAM-1 contributes to numerous inflammations with its strong effect of attracting neutrophiles such as granulocytes and lymphocytes.

Majocchi's disease (also known as Majocchi's Granuloma, "Purpura annularis telangiectodes,", and "Purpura annularis telangiectodes of Majocchi") is well-recognized but uncommon skin condition characterized by purple/bluish-red 1- to 3-cm annular patches composed of dark red telangiectases with petechiae. The name Majocchi's comes from the Professor Domenico Majocchi who first discovered the disorder in 1883. Domenico Majocchi was a professor of dermatology at the University of Parma and later the University of Bologna. Majocchi's disease can be defined as an infection of the dermal and subcutaneous tissues due to a fungal mold infection on the cutaneous layer of the skin. The most common dermatophyte is called "Trichophyton rubrum." This disease can affect both immunocompetent and immunocompromised hosts. However, immunocompromised individuals have a higher risk.

Tufted folliculitis presents with doll's hair-like bundling of follicular units, and is seen in a wide range of scarring conditions including chronic staphylococcal infection, chronic lupus erythematosus, lichen planopilaris, Graham-Little syndrome, folliculitis decalvans, acne keloidalis nuchae, immunobullous disorders, and dissecting cellulitis.

People with recurrent boils are as well more likely to have a positive family history, take antibiotics, and to have been hospitalised, anemic, or diabetic; they are also more likely to have associated skin diseases and multiple lesions.

Other causes include poor immune system function such as from HIV/AIDS, diabetes, malnutrition, or alcoholism. Poor hygiene and obesity have also been linked. It may occur following antibiotic use due to the development of resistance to the antibiotics used. An associated skin disease favors recurrence. This may be attributed to the persistent colonization of abnormal skin with "S. aureus" strains, such as is the case in persons with atopic dermatitis.

Boils which recur under the arm, breast or in the groin area may be associated with hidradenitis suppurativa (HS).

Disseminate and recurrent infundibulofolliculitis or Disseminate and Recurrent Infundibular Folliculitis also called Hitch and Lund disease, is a rare itchy follicular skin condition presents with irregularly shaped papules pierced by hair, mildly pruritic at times, and is chronic with recurrent exacerbations.

Nematode dermatitis is a cutaneous condition characterized by widespread folliculitis caused by "Ancylostoma caninum".

The transmission of Tinea Barbae to humans occurs through contact of an infected animal to the skin of a human. Infection can occasionally be transmitted through contact of infected animal hair on human skin. Tinea Barbae is very rarely transmitted through human to human contact but is not completely impossible.

Fungal folliculitis (also known as Majocchi granuloma) is a skin condition characterized by a deep, pustular type of tinea circinata resembling a carbuncle or kerion.