A fungal infection is the most common cause of nails becoming thick or discolored. It can involve just one or multiple nails. Everyone has many organisms living on their skin and nails; referred to as "normal flora." This normal flora consists of certain bacteria, yeasts, and dermatophytes (fungus). If someone suffers trauma to the nail or is on immune suppressing medication, such as prednisone or chemotherapy, they can become susceptible to the development of a fungal infection on their nails.
A definitive diagnosis can be made by culturing a portion of the nail. Treating the fungal nail infection may involve topical or oral anti-fungals, debridement / thinning of the nail, or improving hygiene by daily washing and drying of the feet. It helps to change socks and shoes at least twice each day and letting air get to the feet when possible. The hardening and discoloration of nails happens to many people of all ages, the good news is that it’s treatable.