Many disorders can affect the nails, including deformities, dystrophies, infections, and ingrown toenails. Infections can involve any part of the nail and may or may not change the nail's appearance. Most nail infections are fungal (onychomycosis—see Onychomycosis), but bacterial and viral infections occur.
Onychomycosis is a fungal infection of the nails.. It is most prevalent among older people, particularly men, and people with poor circulation in the feet (peripheral arterial disease [see Caring for the Feet]), diabetes (see The Foot in Diabetes), a weakened immune system (caused by a disorder or drug), athlete's foot (see Athlete's Foot), or nail dystrophies (see Deformities, Dystrophies, and Discoloration of the Nails). Infected nails have an abnormal appearance but are not itchy or painful. In mild infections, the nails have patches of white or yellow discoloration. A chalky, white scale may slowly spread beneath the nail’s surface. In more severe infections, the nails thicken and appear deformed and discolored. To confirm the diagnosis, the doctor may need to examine a sample of the nail debris under a microscope and sometimes culture it to determine which fungus is causing the infection. These fungal infections are difficult to cure but do not usually cause complications, so treatment is recommended only if symptoms are particularly severe or bothersome or if the person is at risk of complications. If treatment is desired, the doctor usually needs to prescribe a drug taken by mouth. Even after 3 months the nail may appear abnormal. However, the drugs remain bound to the nail plate (the hard part of the nail) and thus continue to be effective after use of the drug is stopped. To reduce the possibility of a recurrence, the nails should be kept trimmed short, the feet should be dried after bathing (including between the toes), absorbent socks should be worn, and antifungal foot powder may be used. Old shoes may contain a high concentration of fungal spores and, if possible, should not be worn.
Ingrown toenail is a condition in which the edges of the nail grow into the surrounding skin. An ingrown nail can result when a deformed toenail grows improperly into the skin or when the skin around the nail grows abnormally fast and engulfs part of the nail. Wearing narrow, ill-fitting shoes and trimming the nail into a curve with short edges rather than straight across can cause or worsen ingrown toenails. Ingrown nails may produce no symptoms at first but eventually may become painful, especially when pressure is applied to the ingrown area. The area is usually red and may be warm. If not treated, the area is prone to infection. Once infected, the area becomes more painful, red, and swollen. Pus may accumulate under the skin next to the nail. For mildly ingrown toenails, the doctor can gently lift the edge of the nail out from under the surrounding skin and place sterile cotton under the nail until the swelling goes away. Sometimes a flexible tube is inserted between the nail and nail fold (the fold of hard skin at the sides of the nail plate where the nail and skin meet) instead of cotton. If an ingrown nail requires further attention, the doctor usually numbs the area with a local anesthetic, then cuts away and removes the ingrown section of nail. The inflammation can then subside, and the ingrown nail usually does not recur.