Here are some common infectious hair diseases:

 

Fungal folliculitis: superficial fungal infections are found in the top layers of the skin; deep fungal infections invade deeper layers of the skin and hair follicles and can spread to the blood or internal organs. According to the infected body area, fungal folliculitis can be classified as tinea capitis (scalp), tinea barbae (beard), tinea corporis (trunk), tinea cruris (groin) and tinea pedis (feet). Fungal infection in or on a part of the body can be divided essentially into three groups: dermatophytic, pityrosporum and candida folliculitis. Dermatophytic folliculitis is caused most often by a zoophilic species, i.e. fungal species that show attraction to or affinity for animals; and the condition presents as follicular pustules surmounting a hardened erythematous (reddened) plaque with peripheral extension. The degree of inflammation is dependant on the depth of fungal penetration, which in turn determines the extent of hair shaft loss. Tinea capitis or ringworm of the head is the most important form of pediatric dermatophytic folliculitis, and has four basic variants – non-inflammatory, black dot, favus and kerion. In the first two forms, there is minimal inflammation and no scarring, whereas the latter two forms present with severe granulomatous and suppurative folliculitis and permanent hair loss. The clinical features of tinea capitis vary considerably depending on the species responsible for the infection. Typically, there is partial alopecia with a varying amount of inflammation. In the non-inflammatory variants, asymmetrical lesions with short broken hair, 1 to 3 mm in length, are observed. Slight inflammation with scaling may be observed on careful inspection. Infection with the zoophilic species tends to produce small lesions with intense inflammation. The most severe inflammatory reactions are called kerion and produce painful boggy masses studded with pustules. These lesions can result in severe hair loss and significant scarring when the disease is in advanced stages. Tinea capitis must be differentiated from seborrheic dermatitis, atopic eczema, psoriasis, alopecia areata, folliculitis, and pseudopelade. The diagnosis of tinea capitis is established by identifying the organism in infected hairs under the microscope. Cultures should be obtained to confirm the diagnosis. Pityrosporum Folliculitis is a condition caused by pityrosporum yeasts, most often Pityrosporum orbiculare, where the yeast gets down into the hair follicles and multiplies, resulting in an itchy eruption. The lesions are reddish follicular papules and pustules located mainly on the upper back, shoulders and chest. Candida folliculitis is folliculitis caused by the Candida species, ubiquitous fungi that most commonly affect humans.

Bacterial folliculitis: develops when bacteria, usually one from the Staphylococcus family of bacteria, enter the body through a cut, scrape, surgical incision, or other break in the skin near a hair follicle. The bacteria can get trapped and the infection may spread to hair follicles on other parts of the body. Bacterial folliculitis may be superficial or deep. Superficial folliculitis, also called impetigo, consists of pustules, which are small-circumscribed elevations of the skin, containing purulent material. The pustules are often surrounded by a ring of redness located within follicular orifices. If the infection of the follicle goes deeper and involves more follicles, it is considered as deep folliculitis and the condition can present as furuncles and carbuncles. These are more serious than folliculitis and can cause permanent damage and scarring. A furuncle is a tender, erythematous, firm or fluctuant mass of walled-off purulent material, arising from the hair follicle, occurring as a result of the spread of the bacterial infection deeper into the tissues of the follicles, beneath the infundibulum. Carbuncles are an aggregate of furuncles that form broad, swollen, erythematous, deep, and painful masses that usually open and drain through multiple tracts. The pus formation in carbuncles is more deeply seated than in the case of furuncles. Necrosis (death) of the intervening skin occurs, and a nodule with a central crater may be seen. Bacterial folliculitis usually occurs in children or adults with a predisposing factor that helps to increase the number of bacteria present on the skin. Staphylococcus Aureus is the most common causative agent, and species of streptococcus, pseudomonas, proteus, and coliform bacteria have also been implicated as causes of bacterial folliculitis.

Viral folliculitis:is an infrequently reported entity involving a variety of viral infections limited to the hair follicle. The clinical presentation of folliculitis caused by the herpes simple virus (HSV) appears as clustered vesicles (small circumscribed elevation of the skin containing serum) on an erythematous (reddened) base. They often progress to form pustular or ulcerated lesions, and eventually a crust. Cases caused by molluscum contagiosum maybe considered a sign of immunosuppression, and the condition manifests as multiple whitish, itchy papules over the beard area. There are also some reports of folliculitis caused by herpes zoster infection. The recommended treatment for viral herpetic folliculitis entails administration of oral antihistamines. There is no single perfect treatment for infection by molluscum contagiosum, and scraping off the bumps using a tool called a curette is a common way to surgically remove them.

Parasitic folliculitis: parasites causing folliculitis are usually small pathogens that burrow into the hair follicle to live there or lay their eggs. Mites such as Demodex folliculorum and Demodex brevis are natural hosts of the human pilo-sebaceous follicle. Head lice (also called pediculus capitis or pediculosis) and humans have evolved together partly due to the fact that head lice depend totally on humans for their existence and do not occur on any other host species. Preserved head lice have been found in the hair of mummies from Egypt buried 5000 years ago. Head lice are a common problem particularly in environments where people are living in close proximity to each other. Transmission occurs by direct contact with an infested person or indirectly by contact with clothing, personal grooming articles, bedding, or upholstered furniture containing viable nits or lice. Although infection is neither life-threatening nor associated with significant complications, it does cause considerable distress, expense and anxiety to those affected. The spectrum of the skin disorders due to these parasites includes: follicular pityriasis (skin disease characterized by epidermal shedding of flaky scales); eruptions of the scalp with or without pus; acne rosacea (a chronic dermatitis of the face characterized by a red or rosy coloration with deep-seated papules and pustules); some cases of blepharitis (inflammation of the eyelids); perioral dermatitis; pustular folliculitis; hyper-pigmented plaques.