A dark line on your nails
Fingernails can reveal just as much about your health as your skin. And although some marks could be due to something like a nutrient deficiency or even something hereditary, a more serious one you should look out for are dark brown or black lines across the nail. This specific mark may be a sign of nail or subungual melanoma which occurs under the nail and affects only 0.7 to 3.5 percent of people with melanoma. Other dots on your nail could be more signs of melanoma, too, including darkened skin around the nail, blood, and splits in the nail, per the American Academy of Dermatology.
