A straight line under your toenails
It could be: Skin cancer. A dark, vertical line underneath a toenail could be acral lentiginous melanoma, or hidden melanoma—a form of the skin cancer that appears on obscure body parts. (Other hidden melanomas include eye melanoma and mouth melanoma.) “It will be a black line from the base of your nail to the end of the nail,” says Pichney.
“It should be seen by a podiatrist or dermatologist. You want to make sure it’s not a fungus, which is usually yellow brown and sporadic throughout the whole nail.” Although only 5 percent of all diagnosed melanoma cases are the hidden kind, hidden melanoma is the most common type in dark-skinned people.
