A: The answer could be something as simple as changing your laundry detergent or fabric softener or more complicated as an allergic reaction to exercise... well not exactly an allergy to working out...
When we exercise, our pores open to allow the body to sweat and cool the body. The various dyes and perfumes from our laundry detergent and fabric softener may react with the open pores and sweat and create a reaction. It could also be a result form the fabric rubbing against your skin causing slight irritation. However, many episodes are caused by an exercise induced histamine response.
Before you swear off exercise claiming you are allergic to working out, there is an easy fix. Histamine is a substance found in the body many of us are familiar with. Anyone who has seasonal allergies are familiar with the itching and inflammation associated with histamine. As you exercise, you create vasodilation, where the veins and arteries expand to increase blood flow, nutrients and oxygen to the affected areas. Histamine is a vasodilator as well. It is ushered to an injured or infected area to help the immune system heal the area. It is believed it may be your body's response to exercise stimulus to help prevent exercise induced fatigue.
The down side... histamine triggers a response in the brain which registers as an "itchy feeling". Your skin may be experiencing the same sensation as the itchy feeling you experience with seasonal allergies in your nose and eyes. An easy fix... take a NON DROWSY antihistamine before you workout to see if that alleviates the problem. The more you exercise, your body will adapt and the muscles and cardiovascular system will become more conditioned. This will allow the body to release less histamine and allow you workout itch free.
* If you find you receive no relief from your exercise induced itch or just think I'm making things up, : ) contact your physician. **This information is not intended to diagnose or prescribe... Always refer to a physician for diagnoses specific to your individual body and situation.