The most common cause of yellowed, thick and /or deformed toenails is a fungal infection of the toenail. The fungus that infects the nail, most commonly, is the same fungus that causes athletes foot. It tends to be slowly progressive, damaging the nail to a greater and greater degree over time. The infection usually starts at the tip of the nail and works its way back. It usually is not painful and often not noticed until it has gotten well established. A single toenail or any number of nails can be affected. It can also occur on just one foot. Over time, the nail becomes thickened, crumbly, and distorted in appearance. Sweaty feet contribute to the initial infection process and contribute to its spread. The fungus prefers an environment that is moist, dark, and warm, which is why it affects the toenails much more often than fingernails. It does not spread through the blood stream. The infection limits itself to the nails and skin. It is often found in association with areas of dry scaly skin on the bottom of the foot or between the toes. The dry scaling skin is frequently found to be chronic athletes' foot. It is not highly contagious, and family members are almost as likely to contract it from some other source as they are from the family member who has the infection. Keeping common showering areas clean is recommended, and sharing shoes should be avoided.
Diagnosis
Not all thicken or yellowed toenails are caused by a fungal infection. Injury to a toenail can cause the toenail to grow in a thickened or malformed fashion. This can be due to an established fungal infection or may be due to the damage caused to the nail root when it was injured. In these instances, treatment with anti-fungal medications will not correct the malformed nail. Other causes of thickened toenails are small bone spurs that can form under the toenail and psoriasis. Taking a scraping of the toenail and culturing it makes the diagnosis.
Treatment
It is best to treat the condition as soon as it is noticed. In early cases, over the counter medications may be sufficient. It is also important to treat any concomitant athlete's foot that may be present. In more advanced cases, a prescription medication may be needed. There are effective topical and oral medications available for the treatment of fungal toenails. If sweating feet are a problem, changing shoes and socks during the day is recommended. There are some topical medications available that help to reduce the sweating of the feet. On occasion, your doctor may recommend removing the toenail.