Black Toenail: How to Know If Its Cancerous

Published November 16, 2020

If you notice a discoloration in your toenails, you’ll probably just shrug it off. After all, toenails get bruised all the time – especially if you’re a bit clumsy. Besides, it doesn’t really cause much discomfort so what’s the big deal?

But as with any type of discoloration in our body, it’s usually a sign that there’s something wrong. In some cases, it can be a sign that cancer is now wreaking havoc in your toenails. And if not treated early on, it can be deadly.

So how do you know if your black toenail is cancer or not? Read on to find out.

Common Causes of Black Toenail

Toenail discoloration is pretty common. That’s why a lot of people don’t really worry about it that much. Among the usual culprits of black toenails are:

• trauma from injury
• repeated trauma (usually a result of constantly bumping your toes against the front of your shoes)
• blood clot under the nailbed
• bacterial infection
• fungal infection

Though these can cause your toenails to turn an unsightly dark color, they’re not always painful. 

But in rare instances, instead of clotting, the blood will pool under your nail bed. This will create pressure between your toe and nail which often results in a smelly discharge.

In even rarer instances, a black toenail can be caused by subungual melanoma. This is a type of malignant tumor that grows under your nailbed causing your toenails to turn black over time.

How to Tell If Its Cancer

Since black toenails look often the same to us, it can be hard to tell if it’s cancer or due to any other causes. Subungual melanoma also develops slowly and has no other symptoms so it only becomes noticeable in its later stages. One study reports that it takes about 2.2 years from the onset of symptoms before a diagnosis can be reached.

But one of the most telling indicators of subungual melanoma is the “Hutchinson’s sign”. This is when the dark stain starts from the nail bed which slowly extends to the cuticles and into the nail folds.

Other symptoms to watch out for include:

• a bruise on the nail that stays in place despite nail growth
• a bruised toenail even without any known injury
• splitting nail or bleeding nail
• nail deterioration (dystrophy)
• skin darkening around the affected nail
• delayed healing of nail lesions or trauma
• painful discharge (pus)
• separation of the nail from the nail bed

In some cases, subungual melanoma won’t cause pigmentation in your toenails. But you may still experience any or all of the other symptoms listed above.

Studies show that it’s a very rare form of cancer, only accounting for 0.7% to 3.5% of all cancerous melanomas worldwide. It mostly occurs in the thumbnails and big toenails, but subungual melanoma can happen on any nail.

Though it’s extremely rare, this type of cancer can be deadly if left untreated. So if you notice the above symptoms, don’t hesitate to consult your doctor.