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|Classification and external resources|
A severe case of athlete's foot
|Classification and external resources|
A severe case of athlete's foot
Athlete's foot (colloquially known as ringworm of the foot, tinea pedis, tinea pedum, and moccasin foot) is a common and contagious dermatophytic fungal infection of the skin that causes scaling, flaking, and itching of the affected areas. Symptoms are caused by fungi such as Epidermophyton floccosum or fungi of the Trichophyton genus such as T. rubrum or T. mentagrophytes. The disease is typically transmitted in moist communal areas where people walk barefoot, such as showers or bathhouses, and requires a warm moist environment, (e.g., the inside of a shoe) to incubate.
The condition typically affects the feet, but may infect or spread to other areas of the body such as the groin and tends to spread to areas of skin that are kept hot and moist, such as with insulation, body heat, and sweat. The fungal agents responsible for infection may be picked up by walking barefoot in an infected area or using an infected towel. Infection can be prevented by limiting the use of occlusive footwear and remaining barefoot. Globally, it affects about 15% of the population.
Athlete's foot is most commonly caused by the fungi Trichophyton rubrum or T. mentagrophytes, but may also be caused by Epidermophyton floccosum. Most cases of athlete's foot in the general population are caused by T. rubrum; however, the majority of athlete's foot cases in athletes are caused by T. mentagrophytes.
Cases of interdigital athlete's foot (between the toes) caused by Trichophyton rubrum may be asymptomatic or have pruritic erythema, scaling, flaking, and maceration (softening and whitening of skin that has been kept wet) of the interdigital spaces between the toes. A complex variant of interdigital athlete's foot caused by T. mentagrophytes is characterized by pain, maceration of the skin, erosions and fissuring of the skin, crusting, and an odor due to bacterial infection of the skin.
Plantar athlete's foot (moccasin foot) is also caused by T. rubrum and typically causes asymptomatic, slightly erythematous plaques to form on the plantar surface (sole) of the foot that are often covered by hyperkeratotic scales. The vesiculobullous type of athlete's foot is usually caused by T. mentagrophytes and is characterized by a sudden outbreak of itchy blisters and vesicles on an erythematous base, usually appearing on the sole of the foot. This subtype of athlete's foot is often complicated by secondary bacterial infection by Streptococcus pyogenes or Staphylococcus aureus.
The fungal infection causing athlete's foot may spread to other areas of the body and is known by a different name after spreading to another region. For example, the infection may be known as tinea corporis when the body or limbs are affected or tinea cruris (jock itch or dhobi itch) when the groin is affected. Athlete's foot most often manifests between the toes, with the space between the fourth and fifth digits most commonly afflicted.
The most common complications of athlete's foot are onychomycosis and cellulitis. 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 underlying infection typically results in the disappearance of the id reaction.
Athlete's foot can usually be diagnosed by visual inspection of the skin, but if the diagnosis is uncertain, direct microscopy of a potassium hydroxide preparation of a skin scraping (known as a KOH test) can confirm the diagnosis of athlete's foot and help rule out other possible causes, such as candidiasis, pitted keratolysis, erythrasma, contact dermatitis, eczema, or psoriasis. Dermatophytes known to cause athlete's foot will demonstrate multiple septate branching hyphae on microscopy.
A Wood's lamp (black light), although useful in diagnosing fungal infections of the scalp (tinea capitis), is not usually helpful in diagnosing athlete's foot, since the common dermatophytes that cause this disease do not fluoresce under ultraviolet light.
The fungi that cause athlete's foot require warmth and moisture to survive and grow. There is an increased risk of infection with exposure to warm, moist environments (e.g., occlusive footwear) and in shared humid environments such as communal showers, shared pools, and treatment tubs.
Due to their insulating nature and the greatly 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. 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).
There are several lifestyle modifications that can be practiced to prevent athlete's foot. Effective preventive measures include keeping the feet dry, using socks made of synthetic materials designed to remove moisture, wearing well ventilated footwear, changing socks frequently, and wearing sandals while walking through communal areas such as gym showers and locker rooms. Recurrence of athlete's foot can be prevented with the use of antifungal powder on the feet.
Without medication, athlete's foot resolves in 30–40% of cases and topical antifungal medication consistently produce much higher percentages of cure. Allylamines such as terbinafine are considered more efficacious than azoles for the treatment of athlete's foot.
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 practicing 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.
There are many topical antifungal drugs useful in the treatment of athlete's foot including: miconazole nitrate, clotrimazole, tolnaftate (a synthetic thiocarbamate), terbinafine hydrochloride, butenafine hydrochloride and undecylenic acid. The fungal infection may be treated with topical antifungal agents, which can take the form of a spray, powder, cream, or gel. Topical application of an antifungal cream such as terbinafine once daily for one week or butenafine once daily for two weeks is effective in most cases of athlete's foot and is more effective than application of miconazole or clotrimazole. Plantar-type athlete's foot is more resistant to topical treatments due to the presence of thickened hyperkeratotic skin on the sole of the foot. Keratolytic and humectant medications such as urea, salicyclic acid, and lactic acid are useful adjunct medications and improve penetration of antifungal agents into the thickened skin. Topical glucocorticoids are sometimes prescribed to alleviate inflammation and pruritus associated with the infection.
For severe or refractory cases of athlete's foot oral terbinafine is more effective than griseofulvin. Fluconazole or itraconazole may also be taken orally for severe athlete's foot infections. The most commonly reported adverse effects from these medications is gastrointestinal upset.
Globally fungal infections affect about 15% of the population and affects one out of five adults. Athlete's foot is more common among adolescents and in individuals who wear occlusive shoes. Studies have demonstrated that men are infected 2–4 times more often than women.
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