I get a rash on my hands and arms every summer is it heat rash?

Every summer i get a  blistery rash on the back of my hands and forearms. After being out in the sunshine for a hour or so, my skin feels like it is burning and i get a tingling sensation. It then beings to itch and a small blistery rash appears. The rash usually disappears after a few days if i stay out of the sun. I have suffered from this embarassing rash since my early teens and have been to numerous doctors about it. However i have just been told that it is heat rash and been giving creams to help stop the itching, which never seem to work.