Toenail fungus forms when fungal bodes called dermatophytes invade the nail bed, growing and multiplying under the protective barrier formed by the toenail. The warm, often damp environment of most shoes provides the ideal environment for the fungus to thrive and cause deep, often difficult-to-treat infection. Treatment is also complicated by the fact that the blood supply to the nails and nail beds is more limited than many other areas, which makes it more difficult for the immune system to fight the infection effectively. The dermatophytes are often found in moist, warm environments like gym locker rooms and public pools, and walking barefoot in these areas can increase the likelihood of infection. The infection can also be spread by wearing shoes or socks of an infected person. Fungal infections are more likely to occur in people with weak immune systems and in those with circulatory problems like those associated with diabetes. Some studies have shown toenail fungal infections are also more common among people who have a family history of nail fungus.
Fungus usually begins as a small whitish or yellowish spot underneath the nail. As the fungus grows and spreads, the entire nail will turn yellow or white and become thick and hardened. The edges and surface may become brittle and ragged. Eventually, the infected toe will develop painful symptoms, especially when pressure is applied or when wearing shoes.
Topical or oral medications are usually used to fight toenail fungus. While many infections can be diagnosed with a visual examination, sometimes a small scraping of material near the toenail will be taken to confirm a diagnosis prior to treatment. In severe infections, all or part of the nail may need to be removed to enable medication to reach the infected area.