Diagnosis directs treatment in fungal infections of the skin.

Dermatophyte fungi are confined to the keratin layer of the epidermis and include three genera: Microsporum, Epidermophyton and Trichophyton. These infections can be transmitted by human contact (anthropophilic), from the soil (geophilic) and by animal (zoophilic) spread. Dermatophyte infections usually present as an erythematous, scaly eruption, which may or may not be itchy. Asymmetry is an important clinical clue to fungal infection, as is annular morphology. Examination under ultraviolet (Wood's light) can be helpful. The gold standard for diagnosing cutaneous fungal infections is microscopy and culture of scale, hair or nail, and a definite diagnosis is desirable before commencing treatment, especially with oral therapy. Any dermatophyte species affecting the body can affect the hands. The most common organism is T. rubrum. Tinea corporis infection affects the trunk mainly in children and adolescents, and all genera of dermatophyte can cause it. Tinea cruris infection involves the groin region and is more common in men than women. T. rubrum is the most common causative dermatophyte. The clinical features of tinea capitis include patchy hair loss with varying degrees of scale, erythema and pustules. Infected hairs tend to break at the base, leaving stubble. Occasionally, there is invasion of the visible epidermis, resulting in a boggy, painful swelling with associated alopecia and regional lymphadenopathy known as a kerion.