A thickened toenail, also known as onychauxis, is a nail condition where the toenail becomes unusually thick. Overtime, the nail may become discolored, brittle, curled and harder to trim. If left untreated, a thickened toenail can lead to discomfort and potential infection.
The thickening of the nail can cause the nail plate (the part you paint with nail polish) to lift away from the nail bed. While toenail fungus can produce similar symptoms, onychauxis is not caused by a fungal infection.