Fungal Nail Infection
Tiny fungi can get inside your nail through a crack or break, causing an infection that can make nails thick, discolored, and brittle. The fungus, which thrives in warm, wet places, can spread to people who swim a lot or who have sweaty feet. An infection won't go away on its own, and it can be hard to treat. Creams you put on your nail may help mild cases. Antifungal pills or surgery to remove the nail offer the best chance of clearing up a severe infection.