Toenail fungus (onychomycosis) is caused by a group of fungi known as dermophytes. This group thrives on skin and on keratin, the main component of hair and nails. The fungus gets under the nail and begins to grow, damaging the nail so it discolors, becoming white, brown or yellow. Eventually, the nail might thicken, harden, become brittle and even fall off.
Athlete’s foot—the most prevalent foot fungus—thrives in warm, sweaty places like the insides of your athletic shoes, which is how it got its name. However, foot fungus can develop in multiple environments, natural and man-made, as long as there is lots of moisture where fungi can grow. These include shared areas at gyms or pools, soil and grass, or even shared items such as shoes, socks, or towels from household members who are infected.  

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.
Besides being exposed to any of the modes of transmission presented above, there are additional risk factors that increase one's chance of contracting athlete's foot. Persons who have had athlete's foot before are more likely to become infected than those who have not. Adults are more likely to catch athlete's foot than children. Men have a higher chance of getting athlete's foot than women.[25] People with diabetes or weakened immune systems[25] are more susceptible to the disease. HIV/AIDS hampers the immune system and increases the risk of acquiring athlete's foot. Hyperhidrosis (abnormally increased sweating) increases the risk of infection and makes treatment more difficult.[26]
Fungal infection occurs when the organism invades through an opening in the nail, meaning fungi will usually attack nails that are already damaged. After infection occurs, the growth of the fungi leads to mild inflammation, which causes the nail to thicken and the nail plate to detach from the nail bed. The space underneath the nail can then serve as a reservoir for bacteria and moulds, which can cause the nail to become discoloured.

Topical treatment (polish or cream) isn’t likely to get rid of a fungal nail infection. Treatment with tablets is considerably more effective and takes less time. But some people can’t take tablets because of the very rare, yet serious risks. How you feel about the pros and cons of the different treatment options is a personal matter. You can also discuss the options with your doctor.


Dermatophytes — fungus that grows on the skin, hair and nails but don’t penetrate tissues of the body. Athlete’s foot or Trichophyton rubrum is the most common dermatophyte and can actually infect the toenails. Infection can also begin by touching objects that have dermatophytes on them, such as nail clippers, nail files, socks, shoes, shower floors, etc. Dermatophytes are the cause of most fungal toenail infections.


Following effective treatment, recurrence is common (10–50%).[2] Nail fungus can be painful and cause permanent damage to nails. It may lead to other serious infections if the immune system is suppressed due to medication, diabetes or other conditions. The risk is most serious for people with diabetes and with immune systems weakened by leukemia or AIDS, or medication after organ transplant. Diabetics have vascular and nerve impairment, and are at risk of cellulitis, a potentially serious bacterial infection; any relatively minor injury to feet, including a nail fungal infection, can lead to more serious complications.[31] Infection of the bone is another rare complication.[6]
Fungi that are already present in or on your body can cause nail infections. If you have come in contact with someone else who has a fungal infection, it may have spread to you. According to the American Academy of Dermatology (AAD), fungal infections affect toenails more commonly than fingernails because your toes are usually confined to your shoes, where they’re in a warm, moist environment.
Athlete’s foot—the most prevalent foot fungus—thrives in warm, sweaty places like the insides of your athletic shoes, which is how it got its name. However, foot fungus can develop in multiple environments, natural and man-made, as long as there is lots of moisture where fungi can grow. These include shared areas at gyms or pools, soil and grass, or even shared items such as shoes, socks, or towels from household members who are infected.  
Fungal athlete's foot may cause a rash on one or both feet and even involve the hand. A "two feet and one hand" pattern is a very common presentation of athlete's foot, especially in men. Hand fungal infections are called tinea manuum. Fungal athlete's foot may also be seen along with ringworm of the groin (especially in men) or hand(s). It is helpful to examine the feet whenever there is a fungal groin rash called tinea cruris, or jock itch. It is important to treat all areas of fungal infection at one time to avoid reinfection. Simply treating the soles and ignoring the concurrent fungal infection of toenails may result in recurrences of athlete's foot.
Toenail fungus, also called onychomycosis, is a common fungal infection of your toenail. The most noticeable symptom is a white, brown, or yellow discoloration of one or more of your toenails. It may spread and cause the nails to thicken or crack. Sandal season or not, toenail fungus typically isn’t what you want to see when you look at your feet. Luckily there are many treatments you can try.
×