When Nails Turn Black?

When the nails change their colour to black, it can be a cause for concern. If there are wide dark lines under the nails, it could be a symptom of melanoma which is a type of skin cancer. If you notice these lines, seek medical help as soon as possible. Moles, trauma, injury, and medication can also cause the nails to change colour. If you have a darker skin tone, it’s normal to have noncancerous dark lines underneath the nails.