“If you notice dark discolouration that is often painful, you should be alarmed,” they warn. “This is a sign of melanoma, which is a very serious form of skin cancer. You should schedule an appointment with your physician right away.”

Healthline adds that dark discolouration could be a sign of subungual melanoma, which is caused when cells in the nail bed create too much melanin, cells that cause colour in things like your skin, hair, and eyes.

The experts outline: “Subungual melanoma develops under the toenail and, depending on the type, can be fatal if left untreated. Most people with subungual melanoma have a dark black, vertical band in a single toenail, which can be confused with other conditions like bacterial and fungal infections or nail injury.”

Apart from a dark band of colour on a nail, Healthline notes that other warning signs of subungual melanoma include:

splitting or bleeding nail
painful nail
drainage (pus) from the nail
injured nails that are slow to heal
nail dystrophy
nails that separate from the nail bed

“If you have any of these and your doctor suspects subungual melanoma, they may order or perform a nail biopsy to check for cancer cells,” the outlet adds.