About Athlete’s Foot (Tinea Pedis)

Tinea refers to all superficial infections caused by dermatophytes. Dermatophytes are fungi that live on keratin in the stratum corneum of the epidermis, hair, nails, and toenails. They cause lesions by infecting these keratin-containing tissues.

Depending on the affected area, tinea is classified as tinea capitis, tinea corporis, tinea cruris, tinea barbae or tinea mustache, tinea faciei, tinea manuum, tinea pedis (athlete’s foot), and tinea unguium. This classification is related to clinical features based on the anatomical site, the thickness of the stratum corneum, and physiological characteristics of keratin in the hair, nails, toenails, and skin. Accordingly, treatment methods and duration also differ.

Among dermatophyte infections, tinea pedis (athlete’s foot) is the most common, accounting for 33–40% of all tinea infections. It is most common in people in their 20s to 40s and is rare in children. In the 1950s, its incidence was relatively low, but as lifestyles changed and people began spending more time wearing shoes and socks at all times, the duration of high moisture in the feet increased, and prevalence has also risen. It is mainly transmitted from foot to foot through keratin shed from infected people in places where many people gather, such as bathhouses and swimming pools, and once infected, a person can pass it on again to family members.

Cause

In a domestic survey of the families of university students, 41.2% showed infection, and based on this, the prevalence in the general population is estimated at 36.5%. In certain occupational groups, prevalence rates of 59.4% and 78.8% were observed. Among people who visited a dermatology clinic in the spring and summer of 1997, the proportion with lesions on the feet was 58% in spring and 76% in summer, and among these, fungal infection accounted for 79.8% in spring and 83.7% in summer. A recent survey showed that it was most common in people aged 50 and older.

The main causative organisms include the following species: Trichophyton rubrum is the most common, and it can also be caused by Trichophyton mentagrophytes, Epidermophyton floccosum, and Microsporum gypseum. In the hyperkeratotic type (characterized by thickened skin on the soles) and the interdigital type (characterized by maceration or cracking between the toes), T. rubrum is common; in the vesicular type (characterized by small blisters on the soles), T. mentagrophytes is more common.

Symptoms

Clinically, it is divided into interdigital, vesicular, and hyperkeratotic types. Generally, the interdigital type is known to be the most common.

1. Interdigital type

This is the most common clinical form of athlete’s foot, occurring most often between the 4th and 5th toes, followed by between the 3rd and 4th toes. It develops easily in these areas because air circulation is poor and moisture is high. Itching is severe, and sweating can cause an unpleasant foot odor. The skin between the toes becomes whitish and macerated, and cracks appear; when it dries, scaling is seen, and it may spread to both toes and the soles. Through damaged skin, secondary bacterial infection may occur.

2. Vesicular type

Small blisters appear scattered on the soles or sides of the feet and may merge, appearing in various sizes and shapes. When the small blisters are filled with sticky fluid, they form a thick yellow-brown crust as they dry, and scratching may leave shallow sores. It tends to worsen in summer because of heavy sweating, and it is very itchy when blisters appear.

3. Hyperkeratotic type (scaly type)

Across the entire sole, keratin of normal skin color becomes thickened, and if scratched, it flakes off like fine powder. It follows a chronic course and causes little itching, so treatment is often delayed.

These three types are often difficult to distinguish clearly, and many cases occur as a combination of multiple types. If the interdigital or vesicular type is scratched or overtreated with keratolytic agents, the skin barrier may be damaged, leading to secondary infection. If it becomes suppurative, it can cause erysipelas and lymphadenitis, and sometimes a dermatophytid reaction on the hands may occur.

Diagnosis

Not all skin lesions on the feet are athlete’s foot, so confirmation through fungal testing is essential before treatment. Such mycological tests include KOH smear examination and fungal culture.

Treatment

Antifungal treatment is the foundation. However, if there is acute inflammation or a secondary infection, wet dressings should be applied first, and complications should be treated with antibiotics and steroids before starting treatment for athlete’s foot. If the skin on the soles is thickened, it is important to remove the keratin first using corn plasters or urea ointment. After that, various antifungal agents are applied twice daily to the lesions and the surrounding area. According to one study, the recurrence rate after topical treatment increased over time, reaching 34.6% after 8 months. If topical treatment does not improve the condition, oral antifungal medication is used. Representative oral antifungal agents include itraconazole, fluconazole, and terbinafine, and these antifungal drugs act on the fungal cell membrane to inhibit fungal growth.

1. Itraconazole

A broad-spectrum antifungal in the triazole class, it is effective not only for athlete’s foot (tinea) but also for candidiasis and Malassezia infections. It inhibits lanosterol demethylation, which is necessary for the synthesis of ergosterol, an essential component of the fungal cell membrane. Typically, 100 mg per day is used, but recently high-dose short-course therapy of 200–400 mg has also been used. This is because a short course of 400 mg for one week in a month can have an effect that lasts for 3–4 months. Side effects include nausea, headache, liver function abnormalities, and anaphylaxis, but these are very rare.

2. Fluconazole

As an antifungal in the triazole class, it can also be used for athlete’s foot. It can be used not only orally but also intravenously, so it is used for systemic fungal infections such as candidiasis and cryptococcosis, but nausea and indigestion may rarely occur as side effects. It is mainly excreted through the kidneys.

3. Terbinafine

An antifungal in the allylamine class, it inhibits squalene epoxidation, which is necessary for ergosterol synthesis in the fungal cell membrane. Squalene accumulated inside the cell has fungicidal effects. It is effective for chronic athlete’s foot of the hands and feet and has the advantage of a low recurrence rate after treatment. Side effects are rare, but indigestion, loss of appetite, and skin rash may occur, and liver function abnormalities are very rare.

So far, this has been an overview of tinea pedis (athlete’s foot).

Source: Korea Disease Control and Prevention Agency National Health Information Portal