The ease with which the fungus spreads to other areas of the body (on one's fingers) poses another complication. When the fungus is spread to other parts of the body, it can easily be spread back to the feet after the feet have been treated. And because the condition is called something else in each place it takes hold (e.g., tinea corporis (ringworm) or tinea cruris (jock itch), persons infected may not be aware it is the same disease.

Research suggests that fungi are sensitive to heat, typically 40–60 °C (104–140 °F). The basis of laser treatment is to try to heat the nail bed to these temperatures in order to disrupt fungal growth.[37] As of 2013 research into laser treatment seems promising.[2] There is also ongoing development in photodynamic therapy, which uses laser or LED light to activate photosensitisers that eradicate fungi.[38]
A 2003 survey of diseases of the foot in 16 European countries found onychomycosis to be the most frequent fungal foot infection and estimates its prevalence at 27%.[32][33] Prevalence was observed to increase with age. In Canada, the prevalence was estimated to be 6.48%.[34] Onychomycosis affects approximately one-third of diabetics[35] and is 56% more frequent in people suffering from psoriasis.[36]
Athlete's foot is divided into four categories or presentations: chronic interdigital athlete's foot, plantar (chronic scaly) athlete's foot (aka "moccasin foot"), acute ulcerative tinea pedis,[11] and vesiculobullous athlete's foot.[2][12][13] "Interdigital" means between the toes. "Plantar" here refers to the sole of the foot. The ulcerative condition includes macerated lesions with scaly borders.[11] Maceration is the softening and breaking down of skin due to extensive exposure to moisture. A vesiculobullous disease is a type of mucocutaneous disease characterized by vesicles and bullae (blisters). Both vesicles and bullae are fluid-filled lesions, and they are distinguished by size (vesicles being less than 5–10 mm and bulla being larger than 5–10 mm, depending upon what definition is used).
Other causative pathogens include Candida and nondermatophytic molds, in particular members of the mold genus Scytalidium (name recently changed to Neoscytalidium), Scopulariopsis, and Aspergillus. Candida species mainly cause fingernail onychomycosis in people whose hands are often submerged in water. Scytalidium mainly affects people in the tropics, though it persists if they later move to areas of temperate climate.
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.[13][23][27] Dermatophytes known to cause athlete's foot will demonstrate multiple septate branching hyphae on microscopy.[13]
Multiple fungi species can infect the nail. Fungus grows well in warm, moist environments such as showers. Fungus infection is one of the few foot problems that affect more men than women, perhaps because more men walk barefoot in locker rooms. Age is a factor, too. Half the sufferers are people older than 70. Other risk factors include having certain medical conditions such as diabetes, vascular insufficiency and malnutrition.
Oral medications include terbinafine (76% effective), itraconazole (60% effective) and fluconazole (48% effective).[2] They share characteristics that enhance their effectiveness: prompt penetration of the nail and nail bed,[23] and persistence in the nail for months after discontinuation of therapy.[24] Ketoconazole by mouth is not recommended due to side effects.[25] Oral terbinafine is better tolerated than itraconazole.[26] For superficial white onychomycosis, systemic rather than topical antifungal therapy is advised.[27]
If common remedies do not offer relief within three to four months of consistent use, or if the discomfort worsens, contact your doctor. Extreme infections may require the temporary surgical removal of the nail. A replacement nail will usually grow. As the new nail regrows, it is good practice to treat it with an antifungal cream to prevent reinfection.
Infected nails are usually thicker than normal and could be warped or oddly shaped. They can break easily. Nails with fungus might look yellow. Sometimes a white dot shows up on the nail and then gets bigger. When fungus builds up under your nail, it can loosen and even separate the nail from the bed. The fungus can also spread to the skin around your nail.