Reasons for black marks on toenails

Written by patricia neill | 13/05/2017
Reasons for black marks on toenails
It pays to check the condition of your toenails occasionally. (walking barefoot in grass image by Nicky Jacobs from

Finger and toenails often reflect the state of health and whether there might be underlying problems. Black marks on the toenails can be caused by many different problems or they can also mean nothing, but it pays to check the nails and ask your family doctor, a dermatologist or a podiatrist if there are any health issues requiring treatment.


Reasons for black marks on toenails
Dropping a heavy object on your toe will cause it to bleed under the nail and turn black. (feet on the balcony image by Wouter Tolenaars from

The first thing to consider with a discoloured toenail is injury. Did you stub a toe or drop something heavy on the nail? Injury to the nail could cause broken capillaries under the nail and the bleeding will cause the nail to look black or reddish black. The toe may swell and you'll feel the pain. Applying cold compresses and painkillers are the way to treat an injured toe.

Runner's Toe

If you run, and your running shoes do not fit properly, then a black toenail may result from ill-fitting socks or shoes. The pressure from each step in a run builds up against the toenail until tissues are injured and capillaries are broken, leading to swelling and black toenails. If pain is slight, runner's toe can be ignored, although addressing the need for appropriate shoes and socks is necessary.

Toenail Fungus

If you get a nail fungus, the first sign will be small white spots, a subtle sign that can be easily missed. This type of infection occurs when you go barefoot in a moist place where people congregate, such as gyms or pool areas. Fungi like a warm, moist environment, which is the usual state of your feet inside your shoes. If the infection progresses without treatment, the toenail may thicken and the nail will become stained with a yellow-brownish colour. At this point, black specks could show up. See your doctor if you suspect you have nail fungus; it is especially dangerous if you are also diabetic.

Bacterial Infection

Reasons for black marks on toenails
Using nail polish can make pretty toenails, but remove it regularly to check for toe problems. (toes image by Tasha from

If you have green or black spots on your toenails, the problem could be a bacterial infection of Pseudomonas aeruginosa, a bacteria that can infect any part of your body. This Gram-negative bacteria lives normally on our bodies and isn't a problem unless it gets into the area between the nail plate and the nail bed through a break in the skin. It might also get trapped between an artificial nail or nail polish and the real nail. The odour of this infection is a sweetish smell. If you suspect this is what is causing the discolouration or your toenail, see a dermatologist.

Warning Sign of Melanoma

Black spots on the toenails could possibly be a sign of melanoma, a very dangerous form of cancer. If none of the other reasons for black spots on your toenails mentioned above seem to fit, visit a doctor immediately to see if it could be melanoma. Early detection is key to treating melanoma, one of the fastest-spreading cancers.

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