How to Prevent Toenail Fungus and Choose the Right Treatment Toenail fungus, medically known as onychomycosis, is a common condition that affects people of all ages. It typically begins as a white or yellow spot under the tip of the toenail and can gradually spread deeper, causing discoloration, thickening, and even crumbling at the edges. Read more.. https://sites.google.com/view/toenail-fungus--treatment/how-to-prevent-toenail-fungus-and-choose-the-right-treatment