I'm 75, and I began to get these in the summer of 2013. They appear on my right lower arm, near the wrist, and the cause seems to be if I carry a heavy weight, or use a screwdriver (a gripping, twisting action). They appear about 24 hours after I have done the action. After a day or two, they begin to fade. They seem to result from some kind of subcutaneous stress, rather than an external blow. I don't treat them in any way, because they don't stay for long.