The dreaded black toenail – Runner’s toe

If you have decided, this spring, that you want to take up running as your form of exercise, Podiatrist, Dennis Rehbock, helps us understand why runner’s toe occurs.

Most runners are prone to getting the dreaded black toenail, technically called a subungual haematoma. However, it is not only runners who develop this. Anyone can get it, depending on the cause.

This condition is from repetitive trauma to a toenail that causes blistering, bruising or bleeding under the nail. The trauma is usually the toe and toenail hitting the upper and front of the shoe and, eventually, causing bleeding under the nail with pain and swelling.

It mostly occurs in long-distance running but also in other ballistic sports, such as tennis and squash. Trail running and general hiking can also cause this black toenail condition.

What causes it?

The mechanism is very simple. The toenail bashes the shoe repetitively and eventually causes a blood blister to form under the nail. Because there is nowhere for the blood blister to go it creates pressure and pain.

The incorrect fitting of the shoe can also cause this to happen. If the shoe is too short and the toe box is too shallow it can exacerbate the injury. This can allow a too-tight or too-loose fitting and can both cause the injury. Also, when combined with downhill running and long-distance running, it can cause the condition.

Trauma, such as dropping a heavy object on the toe can also cause it. Toenails or fingernails could be affected by this traumatic type.

There are other conditions that can also make a toenail go black, but this is best investigated by your podiatrist if none of the above have occurred.

How to treat it?

A small painless black or blue discolouration under a nail is not serious and can be left alone to resolve itself. The bruise will eventually grow out.

A severe large blood blister under the nail would be painful and would need podiatric intervention. This blood blister needs to be opened and drained. This will automatically relieve the pain. The nail may have to have a hole drilled through it to get to the blood blister. This is best performed by a podiatrist and strict antiseptic protocols need to be followed.

A new nail will grow back in three to six months and then precautions need to be taken so that it does not reoccur. For example, the fitting of a running shoe needs to be looked at. It is best to go to a specialised running shoe store to help in the choice of a running shoe and to ensure the fit is correct. Some running shoe brands, like New Balance, have wider and deeper toe boxes for a better shoe fit. Cutting a hole in the running shoe will also help to prevent the toe trauma.

Prevention is better than cure

If the nail and surrounding area becomes very red and has any pus then it would be infected. See your podiatrist or a healthcare professional as soon as possible.

If the nail is white, yellow, of any other unusual colour there may be more going on there that meets the eye. A proper analysis of the nail, where we clip and biopsy a portion of your nail, is necessary.

For a podiatrist in your area look at the Podiatry Association of South Africa website  or call +27 861 100 249.


Dennis Rehbock is a podiatrist in private practice in Johannesburg. He has been a part-time lecturer and clinician at the University of Johannesburg Podiatry Department for 37 years. His special interest includes podiatric sports podiatry and the diabetic foot.