Athlete's Foot

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Overview

Athlete's foot (tinea pedis) is a common persistent infection of the foot caused by a microscopic fungus that lives on dead tissue of the hair, toenails, and outer skin layers (dermatophyte). These fungi thrive in warm, dark, moist environments such as shoes, stockings, and the floors of public showers, locker rooms, and swimming pools.

Athlete's foot is transmitted through contact with a cut or abrasion on the bottom (plantar surface) of the foot. In rare cases, the fungus is transmitted from infected animals to humans.

Dermatophyte (skin) infections cause raised, circular pimples or blisters that resemble the lesions caused by ringworm. The infections are named for the part of the body they infect; therefore, tinea pedis refers to an infection of the feet.

Incidence and Prevalence
Athlete's foot is the most common type of fungal infection. Prevalence of the condition is affected by personal hygiene and daily activity. Athlete's foot is most common in men from the teens to the middle age and in people with compromised immune systems.

Causes

There are at least four dermatophytes that can cause athlete's foot. The most common cause is trichophyton rubrum.

Athlete's foot occurs more often in people who typically experience excessive sweating. The condition is more common in the summertime due to warmer weather. A person does not have to be an athlete to develop athlete's foot.

Signs and Symptoms

There are four common forms of athlete's foot. Common symptoms include persistent itching of the skin on the sole of the foot or between the toes (often the fourth and fifth toes). As the infection progresses, the skin grows soft and the center of the infection becomes inflamed and sensitive to the touch. Gradually, the edges of the infected area become milky white and the skin begins to peel. A slight watery discharge also may be present.

In ulcerative athlete's foot, the peeling skin worsens and large cracks develop in the skin, making the patient susceptible to secondary bacterial infections. The infection can be transmitted to other parts of the body by scratching, or contamination of clothing or bedding.

The third type of tinea pedis is often called "moccasin foot." In this type, a red rash spreads across the lower portion of the foot in the pattern of a moccasin. The skin in this region gradually becomes dense, white, and scaly.

The fourth form of tinea pedis is inflammatory or vesicular, in which a series of raised bumps or ridges develops under the skin on the bottom of the foot, typically in the region of the metatarsal heads. Itching is intense and less skin peeling occurs.

People with acute tinea infections can develop similar symptoms on their hands, typically on the palms. This reaction, also known as tineas manuum, is an immune system response to fungal antigens (i.e., antibodies that fight the fungal infection).

Diagnosis

Diagnosis is made by visual observation of the symptoms. Microscopic examination of skin scrapings is used to determine the type of fungus causing the infection and to rule out bacterial infection. Other tests include growing a fungal culture from skin scrapings and examining the patient's foot under an ultraviolet light.

Treatment

Tinea infections may disappear spontaneously and can persist for years. They are difficult to treat and often recur. Best results usually are obtained with early treatment before the fungal infection establishes itself firmly. Antifungal drugs may be used to fight the infection.

Initial treatment for athlete's foot involves changing the environment that is allowing the fungus to thrive. Mainly, this occurs as a result of a combination between moisture that develops in the shoes and socks and a lack of sunlight to the skin of the feet. An easy firstline remedy is to wear open-toed shoes if possible. Changing the shoes and socks as needed throughout the day, using powder on the feet and between the toes to help absorb moisture, and exposing the feet to sunlight and air as often as possible also may be helpful.

Imidazole drugs combat fungal infections by attacking the enzymes of the fungal cell walls, inhibiting growth and reproduction. Two of these medications, clotrimazole (sold over-the-counter, Lotrimin®) and miconazole (contained in Lotrimin® and Absorbine Jr.®) are available in cream, powder, spray, or liquid form and can be applied topically and massaged into the skin. Side effects are rare and include mild gastrointestinal distress and liver/kidney enzyme problems.

Another imidazole drug, itraconazole (Sporanox®) is available in capsule form. Other preparations in this class include Desenex® and Tinactin®, which contain tolnaftate.

Allylamines can be used to combat stubborn tinea infections. These prescription drugs cause a buildup of compounds that are toxic to fungi, and include terbinafine (contained in Lamisil®) and naftifine (Naftin®).

In most cases, 4 to 6 weeks of treatment clears up the infection. If the infection becomes systemic, stronger antifungal medication may be prescribed. These drugs include griseofulvin (Fulvicin® and Grisactin®) and concentrated forms of terbinafine and itraconazole. Griseofulvin can cause side effects such as headache, nausea, and numbness, so it is used as a last resort.

If the infection is bacterial, oral antibiotics may be prescribed.

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