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Athlete's foot (also known as ringworm of the foot, tinea pedis, tinea pedum, and moccasin foot) is a fungal infection of the skin that causes scaling, flaking, and itch of affected areas, and in severe cases, swelling and amputation of the foot. It is caused by fungi in the genus Trichophyton. The disease is typically transmitted in moist communal areas where people walk barefoot, such as showers or bathhouses, and requires a warm moist environment, such as the inside of a shoe, in order to incubate.
Although the condition typically affects the feet, it can infect or spread to other areas of the body, including the groin, particularly areas of skin that are kept hot and moist, such as with insulation, body heat, and sweat, e.g. in a shoe, for long periods of time. While the fungus is generally picked up through walking barefoot in an infected area or using an infected towel, infection can be prevented by remaining barefoot as this allows the feet to dry properly and removes the fungus' primary incubator - the warm moist interior of a shoe. Athlete's foot can be treated by a very limited number of pharmaceuticals (including creams) and other treatments, although it can be almost completely prevented by never wearing shoes, or wearing them as little as possible.
Globally it affects about 15% of the population.
Signs and 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.
The infection can be spread to other areas of the body, such as 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 or dhobi itch) for an infection of the groin. Tinea pedis most often manifests between the toes, with the space between the fourth and fifth digits most commonly afflicted.
Some individuals may experience an allergic response to the fungus called an "id reaction" in which blisters or vesicles can appear in areas such as the hands, chest and arms. Treatment of the fungus usually results in resolution of the id reaction.
Athlete's foot can usually be diagnosed by visual inspection of the skin, but where the diagnosis is in doubt direct microscopy of a potassium hydroxide preparation (known as a KOH test) may help rule out other possible causes, such as eczema or psoriasis. A KOH preparation is performed by taking skin scrapings which are covered with 10% to 20% potassium hydroxide applied to the microscope slide; after a few minutes the skin cells are degraded by the KOH and the characteristic fungal hyphae can then be seen microscopically, either with or without the assistance of a stain. The KOH preparation has an excellent positive predictive value, but occasionally false negative results may be obtained, especially if treatment with an antifungal medication has already begun.
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 for histological examination.
A Wood's lamp(black light), although useful in diagnosing fungal infections of the scalp (tinea capitis), is not usually helpful in diagnosing tinea pedis, since the common dermatophytes that cause this disease do not fluoresce under ultraviolet light. However, it can be useful for determining if the disease is due to a nonfungal afflictor.
From person to person
Athlete's foot is a communicable disease caused by a parasitic fungus in the genus Trichophyton, either Trichophyton rubrum or Trichophyton mentagrophytes. As the fungus that cause athlete's foot requires warmth and moisture to survive and grow, the primary method of incubation and transmission is when people who regularly wear shoes go barefoot in a moist communal environment, such as a changing room or shower, and then put on shoes.
Due to their insulating nature and the much reduced ventilation of the skin, shoes are the primary cause of the spread of Athlete's Foot. As such, the fungus is only seen in approximately 0.75% of habitually barefoot people. Always being barefoot allows full ventilation around the feet that allows them to remain dry and exposes them to sunlight, as well as developing much stronger skin and causes the fungus to be worn off and removed before it can infect the skin. Also, people who have never worn shoes have splayed toes due to them not being forced to grow firmly pressed together by a shoe. This even further minimizes the chances of infection as it ventilates the warm moist pockets of skin between the third, fourth and fifth toes in shoe-wearing people.
Athlete's Foot can also be transmitted by sharing footwear with an infected person, such as at a bowling alley or any other place that lends footwear. A less common method of infection is through sharing towels. 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).
Since shoes are the primary mode of infection and incubation and since the fungus is almost non-existent in always barefoot cultures due to the prevalence of strong, dry, feet that are very well ventilated, not wearing shoes at all is almost 100% effective in preventing the fungus. People who regularly wear shoes should try to walk barefoot as much as possible in order to prevent infection. Simply remaining barefoot for a few hours after walking through an infected area is usually enough to prevent the fungus growing and wear it off your feet.
When moving through an area that is likely to be infected it is important to remember that the fungus requires the foot to remain moist in order to grow. Since fungi thrive in warm, moist environments, keeping feet as dry as possible and avoiding sharing towels aids prevention. Always dry the feet thoroughly if you wish to put on shoes and ensure that both the shoes and socks are clean and dry and have been regularly washed. In shoe-wearers, hygiene and minimization of shoe use play important roles in preventing transmission. Public showers, borrowed towels, and, particularly, footwear, can all spread the infection from person to person through shared contact followed by incubation in a shoe.
Conventional treatment typically involves daily or twice daily application of a topical medication in conjunction with hygiene measures outlined in the above section on prevention. Keeping feet dry and practising good hygiene is crucial to preventing reinfection. Severe or prolonged fungal skin infections may require treatment with oral antifungal medication. Zinc oxide-based diaper rash ointment may be used; talcum powder can be used to absorb moisture to kill off the infection.
The fungal infection may be treated with topical antifungal agents, which can take the form of a spray, powder, cream, or gel. There exists a large number of antifungal drugs including: miconazole nitrate, clotrimazole, tolnaftate (a synthetic thiocarbamate), terbinafine hydrochloride, butenafine hydrochloride, and undecylenic acid.
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 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 because anti-itch creams typically enhance the moisture content of the skin and encourage fungal growth.
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 (intertriginous) spaces of the toes and at the base of the fingernail or toenail. The hallmark of these infections is a cherry red color surrounding the lesion and a yellow thick pus.
A number of oral antifungals may be used. For severe cases oral terbinafine or itraconazole has greater effectiveness than griseofulvin. Other prescription oral antifungals include fluconazole. The most common adverse effects from these treatment is gastrointestinal upset.
In a 1992 double-blind study of 104 patients, a 10% tea tree oil cream appeared to decrease symptoms but did not show a marked increase of mycological cure over the placebo. However in a 2002 human trial with 158 participants, a 50% dilution of Tea tree oil caused a significant increase in mycological cure rate (64% of as opposed to 31% in placebo). 
Globally it affects about 15% of the population.