Fungus Nail
Fungus nails are a condition which often start as a white discoloration of the edges of the nail, but when established the nail gradually thickens and becomes crumbly with yellowish discoloration affecting the whole nail and the nail bed.
 
The condition is contagious and often can spread to neighbouring nails or to other people. See also nail infection.

This information is for guidance only. If you are in doubt at all, please consult your nearest health professional.