Fungal nail infections, also known as onychomycosis, occur when fungi invade the nails, typically affecting the toenails more than the fingernails. These infections can cause the nails to become discolored, thickened, and brittle. They may also lead to discomfort and pain, especially if left untreated. The fungi responsible for these infections thrive in warm, moist environments, such as inside shoes or public showers. Risk factors include poor circulation, diabetes, and a weakened immune system. Treatment options often involve antifungal medications, either topical or oral, to eliminate the infection and restore healthy nail growth.