Running is one of many ways you can reach the recommended 150 minutes of aerobic exercise suggested by organizations like the American Heart Association and the Centers for Disease Control and Prevention. However, if you have sensitive skin or pre-existing conditions, running may cause varying amounts of irritation to your legs in the form of itching, especially when choosing to run in pants or other garments that completely cover the legs.
Fabric
The types of fabrics you choose for your workout clothing can make a significant difference in your overall comfort while running, especially when choosing longer bottoms instead of running shorts. Certain types of fabrics, like wool or some types of synthetic fabrics, can both scratch and irritate your skin as it rubs up against your legs while running, resulting in an itching sensation on the skin it touches. If the pants are tight on the legs, this can cause further irritation, because fabrics like wool don't breathe. Consider switching to shorts when you go for a run, or choose running pants that are made out of materials like cotton, which both breathes and causes less irritation.
Detergent
When you have sensitive skin, or if you have allergens to soaps or other cleaning products, you may want to look at your laundry detergent, fabric softener or dryer sheet as the culprit for itchy legs while running. Detergents and other cleaning products often contain scents and chemicals that can irritate sensitive skin, resulting in the release of histamine in the body, which causes itching. When washing your clothes, look for products that are hypoallergenic and scent-free to help reduce the chances of itching.
Plants
If your exercise routine involves trail running or any other route that takes you through underbrush or thick forests, your itching may be associated with plant contact. Any plant can cause your legs to itch when wearing shorts, depending on whether or not your skin is sensitive to it, but two common plants in particular, poison ivy and poison oak, can create severe itching when they come into contact with your legs. If your itching is accompanied by swelling, rash or hives, there is a good chance your having an allergic reaction to a plant you brushed against during your run.
Exercise Allergy
In very rare cases, leg itching while running can be associated with an allergy to exercise, commonly known as exercise-induced urticaria. When dealing with exercise urticaria, you will most likely need to see your doctor about prescription options that will allow you to continue exercising without a reaction. In most cases, exercise allergies are not serious, however, in rare cases an exercise allergy can turn into anaphylaxis, which can be deadly if not treated immediately.
