 [ Symptoms ] what does it mean when you exercise and sweat and then begin to itch [ Disease ] this is quite common it is most likely due to an allergic like reaction during exercise during exercise histamines are released and some people are sensitive to them people sensitive to histamines can experience rashes itching and other allergic symptoms during exercise most of the time the rashes appear on the chest and thighs but can be on the arms or neck too sometimes exercise also reacts with food allergies or medications e g antibiotics pain medications sedatives tranquilizers and diuretics to cause the problem if the problem is bothering you so much that you can not stand it and it does not go away during the exercise session it may just pass if you continue then you should ask your doctor about using a topical ointment to stop the itching or taking an over the counter anti histamine like benadryl 30 60 minutes before exercising if over the counter anti histamines make you sleepy your doctor can prescribe a non sedative anti histamine you should only take over the counter or prescription medication for this problem after speaking with your doctor