All of these answers say that this should happen after a long period of inactivity. Well, I was a child athlete, then college athlete and now I can not go through one single day without some type of exercise. So in my case the itching is not because I haven't been active - it couldn't be. I'm a poster child for active.    Also, in addition to my legs and butt I also itch on my belly. I have been unable to find any answers online, and honestly, I'm not interested in drugging myself every time I exercise - that's at least once a day- with benadryl or something else. I don't even take headache medicine...     I'm starting to wonder whether this is related to the arteries just being too small, and the blood cannot flow freely - not just when exercising though. My father just had a triple bypass surgery on his heart because of a poor blood flow. Perhaps I have the same condition, and all of us who suffer from this itch and ARE ACTIVE might have the same problem. This could translate, at least in the future, to further problems. I might give up on the internet and go to a doctor.