Up until now I thought these were severe sunburns or something like that, but I have now come to the conclusion that I have several large birthmarks on my left arm.
They went rather unnoticed until a few years ago when they started getting darker. They look like 'cafe au lait' spots, but they are fairly larger than most I've seen in pictures and cover mostly my forearm and above my elbow. They are much darker than my natural skin tone, meaning I can't cover them up with makeup unless I do the whole arm. They hadn't bothered me so far until they began turning a darker brown color.
I THINK there's four, but they're so irregular in shape that I can't be sure. It actually seems as if someone splashed a liquid of sorts on me. I have a smaller, perfect oval shaped one on the palm of my hand (same arm) that is getting darker as well, though not as much so. Apart from that I have no other birthmarks, aside from a beauty spot on my upper back.
I had read somewhere that six or more was a bad sign, but again, I'm not sure if these ones mean anything. I can attach a picture if needed.