Nail fungus (onychomycosis) is a fungal infection in either a fingernail or a toenail.

The fungal infection causes discoloration and thickening of the nail. Diagnosis can be made through physical examination and a culture of the nail. Other things can cause thickening of the nails or discoloration, including psoriasis and sometimes allergic reactions.

Treatment of nail fungus includes either a prescription topical nail polish or an oral anti-fungal medication.  The oral anti-fungal medication is far more effective than any other treatments.  Laser treatments for nail fungus can be effective but are expensive and have lower percentage effectiveness than the oral route.