Tinea cruris, also known informally as crotch itch or jock itch in American English and dhobi itch or scrot rot in British English, is a dermatophyte fungal infection of the groin region in either sex, though more often seen in males.

Symptoms and signs

As the common name for this condition implies, it causes itching or a burning sensation in the groin area, thigh skin folds, or anus. It may involve the inner thighs and genital areas, as well as extending back to the perineum and perianal areas.

Affected areas may appear red, tan, or brown, with flaking, rippling, peeling, or cracking skin.

The acute infection begins with an area in the groin fold about a half-inch across, usually on both sides. The area may enlarge, and other sores may develop in no particular pattern. The rash appears as raised red plaques (platelike areas) and scaly patches with sharply defined borders that may blister and ooze.

If the rash advances, it usually advances down the inner thigh. The advancing edge is redder and more raised than areas that have been infected longer. The advancing edge is usually scaly, and very easily distinguished or well demarcated.

The skin within the border turns a reddish-brown and loses much of its scale. The border may exhibit tiny pimples or even pustules, with central areas that are reddish and dry with small scales.

If infected with candidal organisms, the rash tends to be redder and wetter. The skin of the penis may be involved, whereas other organisms spare the penis.

Causes

Opportunistic infections (infections that are caused by a diminished immune system) are frequent. Fungus from other parts of the body (commonly tinea pedis or ‘athlete’s foot’) can contribute to jock itch. A warm, damp environment allowing the fungus to cultivate greatly contributes; especially with tight, sweaty or rubbing clothing such as a jockstrap.

The type of fungus that most commonly causes tinea cruris is called Trichophyton rubrum. Some other contributing fungi are Candida albicans, Trichophyton mentagrophytes and Epidermophyton floccosum.

Treatment

Tinea cruris is often treated with antifungal drugs applied topically. Traditionally creams containing tolnaftate, terbinafine, clotrimazole or miconazole have been used, although newer agents such as butenafine are also used. These anti-fungal agents work by stopping the fungi from producing a substance called ergosterol, which is an essential component of fungal cell membranes. If ergosterol synthesis is completely or partially inhibited, the cell is no longer able to construct an intact cell membrane. This leads to death of the fungus.

If the skin inflammation causes discomfort and itching, glucocorticoid steroids may be combined with the anti-fungal drug to help prevent further irritation due to the patient scratching the area. Apart from the quicker relief of symptoms, this also helps minimise the risk of secondary bacterial infection caused by the scratching. However, steroids may exacerbate the condition if used alone for fungal infections.