You may have a nail fungal infection — also called onychomycosis (on-i-ko-mi-KO-sis) — if one or more of your nails are: * Thickened * Brittle, crumbly or ragged* Distorted in shape* Dull, with no luster or shineA dark color, caused by debris building up under your nailInfected nails may also separate from the nail bed, a condition called onycholysis. You may even feel pain in your toes or fingertips and detect a slightly foul odor.