Blackened toenails can be caused by a variety of injuries or medical conditions which require specialized treatment. 

The most common causes of black toenails is dropping something on the toe, or getting stepped on.  This causes injury to the tissue underneath the nail causing it to bleed.  Despite being cosmetically unappealing it can be extremely painful because blood is restricted to filling only a small space, and if bleeding continues painful pressure can build. 

Blood underneath the nail can also begin from repetitive trauma, usually running but can occur with any sport where repetitive movement causes the toenail to be repeatedly traumatized.  This includes sports like tennis, football and especially soccer.  This darkening is not as painful as a direct force trauma, but can be equally unappealing to look at. 

People often treat this condition at home by heating a needle and piercing the nail to allow blood to escape and reduce pressure and pain.  While this helps with pain in the short term, infection can often set in leading to greater complications.   Your podiatrist can remove blood from under your nail to alleviate your pain at the same time reducing your risk of subsequent infection.

It is important to note that if injury was caused by direct trauma, underlying fracture of the bone may have happened.  Tearing of the skin to the underlying nail bed to which the nail attaches may also have occurred.  If these problems are not evaluated and treated by a podiatrist, chronic pain can occur in cases of fracture,  or in cases of nail bed tearing/laceration, infection of the underlying bone which can require amputation of affected toe if not treated early.    A good rule of thumb is that if 50% or more of nail has blood underneath, removal of nail should be performed by a physician to release pressure as well as inspect for integrity of skin to nail bed.   Sometimes chronically black toenails can loosen from underlying skin and may require removal to allow for new healthy nail growth. 

Black toenails that have occurred in individuals who have not been injured or participate in athletics should be evaluated immediately.  The majority of cases can be explained by trauma, fungal infection, or other benign cause, but in rare cases a tumor called a malignant melanoma can occur. 

Melanomas appear like dark spots under the nail and are often associated with a streak of dark coloration to the nail.  Inspection by a physician requires removal and sending a sample of the nail/skin to a pathologist for diagnosis.  

Finally, dark or black toenails can be caused by a simple fungal infection of the nail.  Most fungal toenails will appear yellowed but in darker skin individuals can appear brown to black.  There are many treatments for fungal toenails that your podiatrist can discuss with you. 

See your podiatrist soon to treat those black toenails as earlier treatment results in better outcomes.