Dry skin, dry weather and low humidity are the most common reason people experience itching while exercising. Dry, cold winter air is responsible for most of this seasonal skin irritation. This is also the eaiest irritation to treat, by using a good moisturizer before exercising.
Another common cause of itching is an allergic reaction to a new or different soap, lotion or detergent. If you have itching after trying a new product, simply change products to see if that solves the problem.
Other causes of exercise itching can include reactions between exercise, some food allergies or certain medications. Antibiotics, some pain medications, and diuretics all have been known to cause itching during exercise for some people. If you experience this, tell your doctor or pharmacist about your symptoms and what medication you are taking. Sometimes they will recommend a cream or an over-the-counter anti-histamine before exercise.
Another cause may include urticaria, an allergic reaction that causes the release of histamines that dilate blood vessels and result in swelling and skin irritation. Urticaria is recognized by red, itchy welts or hives on the chest. Urticaria can be triggered by sweating or extreme temperatures. Exercising in a cooler, dryer climate, or lowering your exercise intensity may reduce symptoms.
In rare cases some people devlop exercise-induced anaphylaxis, which can be serious. The symptoms are hives and itching that progresses to shortness of breath, and low blood pressure. This is a serious reaction and if not treated this may lead to shock. If you have such symptoms it is important to tell your doctor before exercising. Symptoms are often treated with antihistamines. Read more about Exercise-induced anaphylaxis