Toenail fungus infection is a common condition that begins through the emergence of a yellow or white spot under your fingernail or toenail. As the toenail infection gets worse, it can change the color of the nails; the nails may also go brittle and may crumble. The infection may also spread to other toenails. If the condition is not severe and it does not bother you, treatment may not be necessary. However, if it is causing you pain and discomfort and it has caused your nails to thicken, then you may need some self-care steps and medications to help. Even if toenail fungus can be treated, it is more likely to recur. Toenail fungus is also known as onychomycosis.