I am a 40yr old male and have no known allergies. I recently developed a problem with my skin. When my body heat rises, I get a stinging prickly feeling on my back, arms, stomach and chest. This becomes extremely painful during exercise but subsides a little when I start to sweat. It can also be set off by being in a hot room. I have developed redness to the back of my upper arms and a few small pimple like bumps on my shoulders. I have had this condition for about 3 weeks.