I have talked often in the past about checking your toe nails for spots. The spot on your nail can be an sign of melanoma. Melanoma of the foot is the most deadly form of melanoma. Why? Because it often goes unnoticed and untreated.
There can be other reasons for spots under your toe nail. The first that comes to mind is a subungual hematoma. A subungal hematoma is blood under the nail. An injury that you would remember is the cause of the blood. It could be that you dropped a dumbbell or something heavy on your toe. (Or somehow dropped a hammer on your toe or worse, accidentally hit your toe with a hammer.) It could be that you stubbed your toe with force against something hard. Generally a subungual hematoma will hurt. The buildup of blood under the nail is the cause of the pain. It also could be that you broke your toe. When you have this kind of injury you have two choices. You can ice the area for the first 24 hours and see if the pain goes away. During that time, you can also take over the counter pain relievers. (If you can tolerate them.) If the pain is intense, it is time to see your friendly local podiatrist. The doctor can check to see if you broke your toe and that is part of the pain. If the pain is from the subungual hematoma, the doctor can drain the blood. This procedure sounds worse than it feels.