Toenail fungus symptoms are usually obvious and easy to catch if you know what you’re looking for. As the fungus grows and damages the hard keratin making up your toenails, the affected areas start to look dull and discolored. Often nails turn a yellow-grey color, though they could simply get darker. Nails often become thickened and distorted in shape as well. The edges may appear ragged or crumbly. Often the keratin grows more brittle, too. Some people’s nails separate from their nail bed and get debris caught under them.