This is a condition where there is a black spot either on the bottom of the heel, back of the heel, or some other part of the foot, and really what it is caused by is rubbing and it creates a little black spot with a blood blister underneath it. This is caused by repetitive rubbing on the foot and it is usually not dangerous. You have to be aware, though, if it gets bigger and doesn't go away, to biopsy the area to make sure it is not a melanoma, but for the most part this goes away. Some types of treatments for it are to trim down the callus tissue over it and to make sure that there is blood underneath there. As well, using something called Glide to reduce the friction on the bottom of the foot.
To Your Health,
Dr. Donald Pelto