Black and Red Toenails
A quick surfing of the internet should suffice to show you that there are myriad causes for black toenails. The most common cause of this phenomenon is bleeding under the nail. This is called subungual hematoma.
Bowling Ball Trauma
If subungual hematoma is the most common cause of blackened toenails, the most common cause of subungual hematoma is direct trauma to the nail. If something heavy falls on your toe, you may find you have this black discoloration on the nail. But not all traumas are as sudden as dropping a bowling ball on your toe.
A black toenail can also result from what is known as microtrauma. This kind of trauma is accumulative in nature and is often seen in runners. What happens is that the toenails bang into the front of the walking shoe over and over again, causing small blood vessels to break beneath the nails. This causes an accumulation of blood to form under the nail.
Any quantity of blood can pool beneath the nail, causing smaller or larger spots as the case may be. The development of hematomas can be quick or slow. A runner may be surprised to find one after a single run, or notice a spot getting bigger over the course of several runs. The main cause of subungual hematomas in runners is poor-fitting shoes.
Shoes that are too tight cause constant pressure to be exerted on the toenails. On the other hand, if the shoes are too loose, your foot may slide into the front of your shoe, over and over again, as you walk or run. This is even more so for runners who like to do their thing on hills or trails. The momentum caused by running on a hill exacerbates the effects of the ill-fitting shoes. Trails have uneven surfaces, so that the foot twists and turns in an unpredictable manner, causing sudden pressure on the nails depending on the dips and meanderings of the trail.
Of course, toenail fungus can also cause the toenails to blacken. Toenail fungus goes through stages of discoloration as it worsens. At first, you may see white splotches, some thickening of the nails, or perhaps a yellow discoloration. Over time, however, toenail fungus may present as a brown or black discoloration. This signifies advanced toenail fungus.
In most cases, there is no need to treat black or red nails. But if there should be pain or infection present, it may be necessary to drain off the blood or in the worst scenario, to remove the nail. It is common for a nail to fall off after major trauma, which is nature's way of handling a now-defective nail so that a new nail can come in. It's typical for a new nail to form within 6-8 months.
There is the very rare possibility that a black discoloration of the nail may signify melanoma. If a black area should appear under the nail, without there having been any known injury, microtrauma, or fungus, it's a good idea to see a podiatrist and have the spot evaluated. If you see that the spot moves up as the nail grows out, there's no risk of melanoma. Still, a cautious doctor may decide to biopsy the area, just to be sure.