Is it somewhere that you wouldn't have noticed it earlier? They're farely common (1 in every 333 people has one) and typically aren't a big deal. They're caused by abnormal formation of veins If you've never noticed it before, it's possible that the skin around that area is thinning and the veins are becomming more visible. Or it might just be in a place that you don't typically notice. My brother started balding a few years back and was surprised to find a port wine stain on a part of his head that had always previously been covered with hair.