What does it mean when your toenail turns black?

While you probably don't think about your feet very often if they're healthy, if something is a bit off — well, then that might not be the case. Discolored toenails, whatever the cause, can be both off-putting and uncomfortable. Broadly speaking, a discolored toenail can signal a nutritional deficiency, infection, or trauma, according to Healthline, but black toenails, specifically, have a multitude of reasons for existing.

It's not usually as worrisome as a changing mole can be (if you notice a changing mole, get into a dermatologist ASAP), but black toenails are never really a welcome sight. Most importantly, of course, if your black toenail gets worse or doesn't go away on its own, consult your doctor immediately as it could need medical attention. 

A black toenail could be a sign of something deeper

Any kind of discoloration that pops up on a toenail, even if you think it's caused by your nail polish (or its often too-harsh remover), can be alarming. Healthline notes, however, that a black toenail specifically may signal an underlying medical condition such as anemia, diabetes, or even heart or kidney disease. 

Likewise, fungal infections can sometimes cause your toenail to turn black due to debris build-up. Toenails are particularly susceptible to such infections because they thrive in moist and warm environments, such as those created by your sock-and shoe-covered feet.

Most worryingly, melanoma, the most serious type of skin cancer, typically presents as a dark brown misshapen spot, which may arise under a nail bed. 

A dark spot on the toenail isn't always the worst-case scenario, though. If you've hit your toe recently, the trauma to the toenail can cause blood vessels underneath to break, resulting in bleeding — this can look black underneath a nail.

Most of the time, a black toenail is easily treatable

Medical News Today explained that most often there's no cause for worry if you have a black toenail. In fact, the vast majority of the time, this won't even require a doctor's visit — but also, this is more true if you know what caused it, like if you stubbed your toe recently. 

If you have no idea what's happened, seeing your doctor might be your best bet (if you suffer from diabetes, definitely see your doctor right away just in case). For example, if you do have a fungal infection and you don't treat it, the fungus can spread to other feet and even other parts of your body, and can cause permanent nail damage.

If your black toenail is the result of trauma, it should heal over time. However, if your toenail has a black spot and doesn't get better, have it checked out just in case to be on the safe side.