Occasional itching is a normal, common experience. Sometimes, though, it can result from a specific stimuli, such as allergies, environmental factors and even serious medical conditions. If you experience itching during your daily run, it may be caused by circulatory reactions in your skin.
Blood Flow Reactions Can Cause Itching
If you are new to exercise, you may have decreased capillary blood flow. Even if you exercise regularly, only 20 to 25 percent of capillaries are open when you rest. Blood flow increases 15 to 20 times with exercise, opening 100 percent of your capillaries. As your muscles demands more oxygen to fuel activity, your body secretes epinephrine and increases sympathetic stimulation that causes narrowing of blood vessels in your skin and internal organs. Many people experience this adjustment to exercise as itchy skin.
Exercise-Induced Allergy -- Cholinergic Urticaria
If you experience skin eruptions -- such as hives or welts -- along with itching, you could be dealing with cholinergic urticaria, an allergic reaction. It can be caused by increased histamine levels triggered by a rise in temperature during exercise. Stop running if an itchy rash occurs, and limit exercise until your body adjusts to new levels of activity. Unchecked, cholinergic urticaria can advance to a potentially life-threatening condition called exercise-induced anaphylaxis. Seek medical attention if you experience a rash, hives or difficulty breathing while exercising.