I've been trying to figure out what this red mark is on my arm. I've had it for several year and before it just a red mark that would come and go, but within the last year, it's starting to appear as more than just a red shape. It's located on the upper part of my right arm. The hardest part about this is showing someone when the mark just comes and goes and I have no control over when it appears or disappears. I've tried googling it but it's hard to be descriptive and try to figure it out. I've yet to go to a doctors but I'm only 21 and I don't know if it's something I should get checked or not. Any advice would be greatly appreciated.