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Cutaneous fungal infections are categorized as follows:
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Superficial: infecting the stratum corneum, hair, and nails.
The three major genera are Trichophyton, Microsporum, and Epidermophyton. The term “tinea” is used to denote fungal infection and is typically modified by body site (e.g., tinea capitis, tinea corporis).
Candida is a normal inhabitant of the oropharynx and gastrointestinal tract. Moist, wet conditions favor Candida overgrowth and can lead to superficial infection of the skin or mucosal surfaces.
Deep: involving the dermis and subcutaneous tissues.
Subcutaneous mycoses are the result of implantation and include chromoblastomycosis, mycetoma, sporotrichosis, basidiobolomycosis, and lobomycosis.
Deep mycoses are the result of hematogenous spread or extension from an underlying structure. True pathogens infect hosts with normal immunity and include histoplasmosis, coccidioidomycosis, and paracoccidioidomycosis. Opportunistic pathogens infect immunocompromised hosts and include disseminated candidiasis and aspergillosis.
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SUPERFICIAL DERMATOPHYTOSES
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Tinea capitis is a fungal infection (Microsporum or Trichophyton) of the scalp and hair characterized by follicular inflammation with painful, boggy nodules that drain pus and result in hair loss.
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INSIGHT 
If there is any doubt about the diagnosis, a fungal culture of affected hairs and scale can be very helpful. If systemic treatment is given without improvement, the initial diagnosis is called into question, but culture after treatment is extremely low-yield.
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SYNONYMS Scalp ringworm, tinea tonsurans, herpes tonsurans, hair ringworm.
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AGE Children: 2 to 10 years; rarely seen in infants or adults.
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INCIDENCE Most common fungal infection in childhood. Up to 8% of the pediatric population affected.
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ETIOLOGY Trichophyton tonsurans (90%) in the United States and West Europe > Microsporum canis > M. audouinii > T. verrucosum. T. violaceum > T. tonsurans in Southeast Europe and North Africa.
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Two to four days after exposure, scaly pruritic patches appear in the scalp with hair loss. Untreated, the lesions enlarge and boggy papular lesions may develop within the alopecic patches. Systemic symptoms may include cervical lymphadenopathy, malaise, or fever. Additionally, a systemic allergy to fungal elements can be seen (see “Tinea and Id Reaction”).
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Ectothrix (infection on the outside of the hair shaft).
Gray patch ringworm. Brittle hair; shafts break off 1 to 2 mm above the scalp surface. Broken hairs give patch a grayish appearance. Caused by M. audouinii and M. canis (Fig. 21-1).
Endothrix (infection on the inside of the hair shaft).
Black dot ringworm. Broken-off hair shafts flush with the level of the scalp give the appearance of black dots, caused by T. tonsurans and T. violaceum (Fig. 21-2). Easily spread ...