Tinea Cruris: Causes, Diagnosis and Treatment

What tinea cruris is

Dermatophytes are fungi that live on dead keratin, the protein in the outer layer of skin, hair and nails. In the warm, moist environment of the groin, they multiply and trigger an inflammatory response at the edge of the patch, where the fungus is most active. That is why the edge is red and scaly while the center can look clearer.

Tinea cruris is the medical name for what most people call jock itch. For a practical guide to symptoms, scrotal itching and everyday prevention, see that page. This page focuses on the causes, diagnosis and treatment of difficult cases.

The fungi that cause it

The fungi spread through direct skin contact, shared towels and clothing, and from your own feet. Many people transfer athlete's foot fungi to the groin on their hands or when pulling up underwear.

Risk factors

• untreated athlete's foot or fungal toenails
• heat, humidity and heavy sweating
• tight, non-breathable clothing and staying in wet swimwear or sports gear
• obesity and skin folds
• diabetes and a weakened immune system
• sharing towels, contact sports and shared locker rooms
• male sex (women get it less often but are not immune)
• using steroid creams on the groin

Symptoms and appearance

• itching, burning or stinging in the groin crease and inner thigh
• a red, pink or brown patch, spreading outward in an arc or half-moon
• a well-defined, raised, scaly or pimply border
• a clearer or brownish center
• spread to the buttocks, lower abdomen or perianal area in longer-standing cases
• in darker skin, the rash may look brown, gray or purple rather than red

The scrotum and penis are usually spared. Involvement of the scrotum suggests yeast (candidiasis) or another cause.

Tinea incognito

When a steroid cream or a combination cream containing a steroid is used on tinea, the redness and itch may improve at first, but the fungus spreads under the cover of suppressed inflammation. The rash becomes larger, less defined, and may develop pustules or nodules. This tinea incognito is a common reason for "jock itch that won't go away".

How tinea cruris differs from look-alikes

Diagnosis

Many typical cases are diagnosed by appearance. Testing is recommended when the diagnosis is unclear, when the rash has not responded to treatment, or before prescribing oral antifungals:

• KOH preparation: skin scraped from the active edge is mixed with potassium hydroxide and examined under a microscope for branching fungal threads (hyphae). Results are available in minutes. Stop antifungal creams for about a week beforehand if possible, to avoid a false negative.
• Fungal culture: identifies the species over 2 to 4 weeks, useful for recurrent or resistant cases.
• PCR testing: faster species identification, and some labs can test for resistance-linked gene changes.
• Wood's lamp: dermatophytes in the groin do not glow, which helps distinguish erythrasma.

Treatment

Topical antifungals (first line)

• Allylamines: terbinafine or naftifine cream, once or twice daily, usually for 1 to 2 weeks.
• Azoles: clotrimazole, miconazole, ketoconazole, econazole or luliconazole, usually twice daily for 2 to 4 weeks.

Apply a thin layer to the rash and about 2 cm (1 inch) beyond the edge. Continue for at least 1 to 2 weeks after the skin looks clear. Nystatin does not work against dermatophytes.

Oral antifungals

Used for extensive rashes, failure of topical treatment, immune suppression, or hair follicle involvement:

• terbinafine tablets for 1 to 2 weeks or longer
• itraconazole for 1 to 2 weeks, preferred for suspected T. indotineae
• fluconazole in some cases

Oral antifungals can interact with other medicines and occasionally affect the liver, so your doctor will review your medicines.

Resistant ringworm

Trichophyton indotineae causes widespread, very itchy and often recurrent ringworm of the groin, buttocks and trunk. It is frequently resistant to terbinafine and spreads between household members and through sexual contact. The CDC advises clinicians to consider it in people with extensive tinea not responding to standard treatment, especially with travel to South Asia. Treatment usually requires several weeks to months of itraconazole, guided by culture.

Preventing recurrence

• Treat athlete's foot and toenail fungus at the same time.
• Dry the groin thoroughly after showering, and dry your feet last or use a separate towel.
• Put on socks before underwear to avoid carrying fungus from feet to groin.
• Wear loose, breathable cotton underwear and change out of sweaty clothes promptly.
• Wash towels, underwear and gym clothes in hot water, and do not share them.
• Use an antifungal powder in the groin during hot weather or training.
• Avoid steroid or combination steroid-antifungal creams unless a doctor prescribes them for a specific reason.
• Lose excess weight and manage blood sugar if you have diabetes.

Frequently asked questions

What causes tinea cruris?

Tinea cruris is caused by dermatophyte fungi, most often Trichophyton rubrum. They thrive in warm, moist skin and spread by contact with infected skin, shared towels or clothing, or from your own athlete's foot. Sweating, tight clothing and diabetes increase the risk.

How is tinea cruris diagnosed?

Doctors often diagnose it from the typical scaly, advancing edge. If unsure, they scrape skin from the edge for a KOH microscope test, which shows fungal threads within minutes. A fungal culture or PCR identifies the species in recurrent or resistant cases.

Why does my tinea cruris keep coming back?

Common reasons are stopping treatment once the itch eases, untreated athlete's foot or nail fungus, steroid creams that let the fungus spread, re-infection from towels or partners, and resistant fungi. A skin scraping and culture help choose the right treatment.

Can women get tinea cruris?

Yes. Women get tinea cruris less often than men, but it occurs, especially with obesity, diabetes, tight clothing or athlete's foot. It looks the same, with an itchy, scaly rash in the groin creases and inner thighs, and is treated the same way.

Is tinea cruris the same as jock itch?

Yes. Tinea cruris is the medical name for jock itch, a dermatophyte fungal infection of the groin. Other groin rashes, such as yeast infections, erythrasma and inverse psoriasis, are sometimes called jock itch but need different treatment.