Athlete's foot

This article describes a medical condition. For the American retail shoe store, see The Athlete's Foot

Athlete's foot or Tinea pedis^[1] is a parasitic fungal infection of the epidermis of the foot. It is typically caused by a mold^[2] (but in some cases a yeast) that grows on the surface of the skin and then into the living skin tissue itself, causing the infection. It usually occurs between the toes, but in severely lasting cases may appear as an extensive "moccasin" pattern on the bottom and sides of the foot. The malady more commonly affects males than females.^[3] Tinea pedis is estimated to be the second most common skin disease in the United States, after acne.^[4] Up to 15% of the U.S. population may have tinea pedis.^[5]

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Causes

The body normally hosts a variety of saprotrophic micro-organisms that rapidly cause infection. Athlete's foot is a layman's description of a skin fungal infection, and is medically referred to as tinea pedis. It may be associated with several different fungi, including yeasts. The most common fungi causing tinea pedis are Trichophyton rubrum and T. mentagrophytes. Fungal infections of the skin are called dermatophytosis. Dermatophytes may be spread from other humans (anthropophilic), animals (zoophilic) or may come from the soil (geophilic). Anthropophillic dermatophytes are restricted to human hosts and produce a mild, chronic inflammation. Zoophilic organisms are found primarily in animals and cause marked inflammatory reactions in humans who have contact with infected cats, dogs, cattle, horses, birds, or other animals. Geophilic species are usually recovered from the soil but occasionally infect humans and animals. They cause a marked inflammatory reaction, which limits the spread of the infection and may lead to a spontaneous cure but may also leave scars. Infections or infestations occur when dermatophytes grow and multiply in the skin.

Symptoms   Athlete's foot causes scaling, flaking and itching of the affected skin. Blisters and cracked skin may also occur, leading to exposed raw tissue, pain, swelling and inflammation. Secondary bacterial infection can accompany the fungal infection, sometimes requiring a course of oral antibiotics.^[6][7]

The infection can be spread to other areas of the body, such as the armpits, knees, elbows, and the groin, and usually is called by a different name once it spreads (such as tinea corporis on the body or limbs and tinea cruris (jock itch) for an infection of the groin).

Tinea pedis most often manifests between the toes, with the webspace between the fourth and fifth digits most commonly afflicted.^[8][9][10]

Diagnosis

Diagnosis can be performed by a general practitioner or by a specialist (either a dermatologist or podiatrist).

Although athlete's foot can usually be diagnosed by visual inspection of the skin, the diagnosis should always include direct microscopy of a potassium hydroxide preparation (known as a KOH test) at the start of treatment to rule out other possible causes, such as eczema or psoriasis.^[11] A KOH preparation is performed on skin scrapings from the affected area. The KOH preparation has an excellent positive predictive value, but occasionally false negative results may be obtained, especially if treatment with an anti-fungal medication has already begun.^[8]

A microbiological culture of skin scrapings can be used in diagnosis, but the process takes several weeks and can often give false negative results.

Tinea infections are sometimes misdiagnosed as atopic dermatitis or allergic eczema,^[8] underscoring the importance of a KOH preparation or microbiological culture being performed before treatment is initiated.

If the above diagnoses are inconclusive or if a treatment regimen has already been started, a biopsy of the affected skin (i.e. a sample of the living skin tissue) can be taken and histological examination of the tissue performed.

A Wood's lamp, although useful in diagnosing fungal infections of the hair (Tinea capitis), is not usually helpful in diagnosing tinea pedis since the common dermatophytes that cause this disease do not fluoresce under ultraviolet light.^[8] However, it can be useful for determining if the disease is due to a non-fungal source.

Transmission

Transmission from person to person

Athlete's foot is caused by a parasitic fungus and is a communicable disease.^[12] It is typically transmitted in moist environments where people walk barefoot, such as showers, bath houses, and locker rooms.^[13][3][12] It can also be transmitted by sharing footwear with an infected person, or less commonly, by sharing towels with an infected person.

Transmission to other parts of the body

The various parasitic fungi that cause athlete's foot can also cause skin infections on other areas of the body, most often under toenails (Onychomycosis) or on the groin (tinea cruris).

Prevention

The practices given in this section do not only help prevent spread of the fungus, they can also help greatly in managing and curing athlete's foot in an individual by reducing or eliminating re-exposure to the fungus in one's home environment.

The fungi that cause athlete's foot can live on shower floors, wet towels, and footwear. Athlete's foot is caused by a fungus and can spread from person to person from shared contact with showers, towels, etc. Hygiene therefore plays an important role in managing an athlete's foot infection. Since fungi thrive in moist environments, it is very important to keep feet and footwear as dry as possible.

Prevention measures in the home

The fungi that cause athlete's foot live on moist surfaces and can be transmitted from an infected person to members of the same household through secondary contact.^[14] By controlling the fungus growth in the household, transmission of the infection can be prevented.

Bathroom hygiene

• Spray tub and bathroom floor with disinfectant after each use to help prevent reinfection and infection of other household members.

Frequent laundering

• Wash sheets, towels, socks, underwear, and bedclothes in hot water (at 60 °C / 140 °F) to kill the fungus.
• Change towels and bed sheets at least once per week.

Avoid sharing

• Avoid sharing of towels, shoes and socks between household members.
• Use a separate towel for drying infected skin areas.

Prevention measures in public places

• Wear shower shoes or sandals in locker rooms, public showers, and public baths.
• Wash feet, particularly between the toes, with soap and dry thoroughly after bathing or showering.
• If you have experienced an infection previously, you may want to treat your feet and shoes with over the counter anti-fungal sprays after using public facilities.

Personal prevention measures

• Dry feet well after showering, paying particular attention to the web space between the toes.
• Try to limit the amount that your feet sweat by wearing open-toed shoes or well-ventilated shoes, such as lightweight mesh running shoes.
• Wear lightweight cotton socks to help reduce sweat.
• Use foot powder to help reduce sweat. Some foot powders also include an anti-fungal ingredient.
• Wear open-toed shoes or simply light-weight socks without shoes when at home.
• Keep shoes dry by wearing a different pair each day.
• Change socks and shoes after exercise.
• Replace sole inserts in shoes/sneakers on a frequent basis.
• Replace old sneakers and exercise shoes.

Treatments

There are many conventional medications (over-the-counter and prescription) as well as alternative treatments for fungal skin infections, including athlete's foot. Important with any treatment plan is the practice of good hygiene. Several placebo controlled studies report that good foot hygiene alone can cure athlete's foot even without medication in 30-40% of the cases.^[15] However, placebo-controlled trials of allylamines and azoles for athlete’s foot consistently produce much higher percentages of cure than placebo.^[16]

Conventional treatments

Conventional treatment typically involves daily or twice daily application of a topical medication in conjunction with hygiene measures outlines in the above section on prevention. Keeping feet dry and practicing good hygiene is crucial to preventing reinfection. Severe or prolonged fungal skin infections may require treatment with oral anti-fungal medication.

Topical medications

Main article: Antifungal drug

The fungal infection is often treated with topical antifungal agents, which can take the form of a spray, powder, cream, or gel. The most common ingredients in over-the-counter products are Miconazole nitrate (2% typical concentration in the United States) and Tolnaftate (1% typ. in the U.S.). Terbinafine, marketed as Lamisil is another over-the-counter drug. There exists a large number of prescription antifungal drugs, from several different drug families. These include ketaconazole, itraconazole, naftifine, nystatin, caspofungin. Studies show that Allylamines (Terbinafine, Amorolfine, Naftifine, Butenafine) cure slightly more infections than azoles (Miconazole, ketaconazole, Clotrimazole, itraconazole, sertaconazole, etc.).^[16]

The time line for cure may be long, often 45 days or longer. The recommended course of treatment is to continue to use the topical treatment for four weeks after the symptoms have subsided to ensure that the fungus has been completely eliminated. However, because the itching associated with the infection subsides quickly, patients may not complete the courses of therapy prescribed.

Anti-itch creams are not recommended as they will alleviate the symptoms but will exacerbate the fungus; this is due to the fact that anti-itch creams typically enhance the moisture content of the skin and encourage fungal growth. For the same reason, some drug manufacturers are using a gel instead of a cream for application of topical drugs (for example, naftin and lamisil). Novartis, maker of lamisil claims that gel penetrates the skin more quickly than cream.

Some topical applications such as carbol fuchsin (also known in the US as Castellani's paint), often used for intertrigo, work well but in small selected areas. This red dye, used in this treatment like many other vital stains, is both fungicidal and bacteriocidal; however, because of the staining it is cosmetically undesirable. For many years gentian violet was also used for bacterial and fungal infections between fingers or toes.

Undecylenic acid (castor oil derivative) is a known fungicide that can be used for fungal skin infections such as athlete's foot.

If the fungal invader is not a dermatophyte but a yeast, other medications such as fluconazole may be used. Typically fluconazole is used for candidal vaginal infections moniliasis but has been shown to be of benefit for those with cutaneous yeast infections as well. The most common of these infections occur in the web spaces (intertriginous) of the toes and at the base of the fingernail or toenail. The hall mark of these infections is a cherry red color surrounding the lesion and a yellow thick pus.

Oral medications

Oral treatment with griseofulvin was begun early in the 1950s. Because of the tendency to cause liver problems and to provoke aplastic anemia the drugs were used cautiously and sparingly. Over time it was found that those problems were due to the size of the crystal in the manufacturing process and microsize and now ultramicrosize crystals are available with few of the original side effects.^{[citation needed]}

For severe cases, the current preferred oral agent in the UK,^[17] is the more effective terbinafine.^[18] Other prescription oral antifungals include itraconazole and fluconazole.^[6]

Alternative treatments

Topical oils

Symptomatic relief from itching may be achieved after topical application of tea tree oil or crocodile oil, probably due to its involvement in the histamine response,^[19] however the efficacy of Tea tree oil in the treatment of athlete's foot (achieving mycological cure) is questionable.^[20][21]

Onion extract

A study of the effect of 3% (v/v) aqueous onion extract was shown to be effective in laboratory conditions against Trichophyton mentagrophytes and T. rubrum.^[22]

Rubbing alcohol and hydrogen peroxide

Direct application of rubbing alcohol and/or hydrogen peroxide after bathing can aid in killing the fungus at the surface level of the skin and will help prevent a secondary (bacterial) infection from occurring.

Hair dryer

Since fungi grow in moist conditions, it is very important to dry the feet well after bathing. A hair dryer can be used to aid the drying process, or to dry feet which have become slightly moist in between showers or baths.

Baking soda

Rubbing feet with a baking soda paste and/or sprinkling baking soda in shoes is thought to help by changing pH.

Household Bleach not recommendable

The use of household bleach as a direct topical application or soak for tinea pedis is not recommended, as it is a well documented irritant (clearly labelled in the United Kingdom as "Harmful" by COSHH). It is used diluted as an environmental decontaminatant to prevent the spread of dermatophytes between animals, and from animals to humans.^[23]

Origin of the term "athlete's foot"

The Oxford English Dictionary documents written usage of the term in 1928 (1928 Lit. Digest 22 December. 16/1), which seems to undercut the claim by W. F. Young, Inc. that the term "athlete's foot" was originated, rather than simply popularized, as part of an advertising campaign for Absorbine Jr. during the 1930s.^[24]

See also

• Tinea
• Tinea cruris "Jock Itch"
• Tinea capitis Fungal infection of the scalp
• Onychomycosis Fungal infection of the finger nails and toenails
• Tinea unguium The most common type of fungal infection of the finger nails and toenails
• Dermatophyte The parasitic fungi that cause tinea
• Ringworm
• Antifungal drugs