A fungal nail infection occurs when a fungus attacks a fingernail, toenail, or the skin under the nail, called the nail bed. Fungal nail infections are not usually painful at first, but if left untreated, the infection may spread and cause complications, such as cellulitis skin infection. A fungal nail infection could lead to more serious problems if you have diabetes or a weakened immune system. Athlete’s Foot often contributes to fungal nails, so treating Athlete’s Foot is advisable. If your toenails have become thick, discoloured and uncomfortable, a visit to the podiatrist is strongly advised. The nail(s) can be thinned, which reduces thickness and pressure. Alternatively, a sufferer could purchase over-the-counter fungal treatments or see the GP for prescribed medication.