The most reliable way to diagnose athlete’s foot is to correctly identify its cause. Fungal athlete's foot is relatively straightforward to diagnose and treat. Visualization of the fungus in skin scrapings removed from the affected areas of the feet is a painless and cost-effective method for diagnosis. Rarely, it is necessary to identify fungi in portions of skin removed during a biopsy. If no fungus is found, other causes of athlete's foot must be investigated.

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]
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Red or black nails due to a hematoma, or blood under the nail, usually occur from trauma (like whacking yourself on the thumb with a hammer). The discolored area will grow out with the nail and be trimmed off as you trim your nails. If you have a black spot under your nail that was not caused by trauma, you may want to see a dermatologist or a podiatrist if it involves a toenail to make sure it is not melanoma (a type of skin cancer associated with pigmented cells). A simple biopsy can rule out malignancy (cancer).
Some methods of prevention include avoiding walking barefoot in public showers, keeping the toenails short, wearing big enough shoes, and changing socks daily.[4][5] When infected, the feet should be kept dry and clean and wearing sandals may help.[3] Treatment can be either with antifungal medication applied to the skin such as clotrimazole or for persistent infections antifungal medication that are taken by mouth such as terbinafine.[2][4] The use of the cream is typically recommended for four weeks.[4]
Topical treatment is also usually recommended for children. One reason for this is that most oral medications aren’t suitable for children. Another reason is that children have thinner nails that grow more quickly, so it’s assumed that treatment with nail polish or creams is more likely to work in children than in adults. White superficial onychomycosis is also often treated with a nail polish or cream.

The fungi (molds) 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—shoes or boots that enclose the feet) and in shared humid environments such as communal showers, shared pools, and treatment tubs.[17] Chlorine bleach is a disinfectant and common household cleaner that kills mold. Cleaning surfaces with a chlorine bleach solution prevents the disease from spreading from subsequent contact. Cleaning bathtubs, showers, bathroom floors, sinks, and counters with bleach helps prevent the spread of the disease, including reinfection.
Modern treatments made surgery a last resort. “Before we had these 21st century medications, we didn’t have a good choice in how to deal with toenail fungus,” said Dr. Hinkes. “Oftentimes patients would come in, and out of frustration and lack of any real significant clinical cure with medication, they would ask for their nails to be permanently removed.”
Use soap and water to wash your feet, and dry well, including between toes. Trim your toenails -- straight across -- to keep them shorter than the end of your toe. Make sure the tools you use are clean, too. Wash clippers and files with soap and water, then wipe with rubbing alcohol. You might be tempted to cover up discolored nails with polish, but don't. Your nail bed can't "breathe," which keeps fungus from going away.
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