If you notice itching start well after you’ve already acclimated to running—especially if you notice physical hives with it—you might have a condition called exercise-induced urticaria, says Lily Pien, M.D., an allergist and associate professor of medicine at the Cleveland Clinic. Experts don’t know exactly why it occurs, but they believe it may have to do with a heightened response or sensitivity by your allergic mast cells.
Exercise-induced urticaria usually comes on soon after your body temperature and heart rate start to rise during your workout and you begin to sweat, says Pien. So you’re more likely to notice it with higher-exertion aerobic exercise like running than with lower intensity workouts like walking.
Along with the itchiness, you might also start to feel hot, and notice the development of small hives. These hives can look like raised welts or like red splotches, blotches, or blisters, according to the American Academy of Family Physicians. While they can occur anywhere, they usually tend to develop on your torso, says Pien. (Burns, who experienced exercise-induced hives sporadically as a teen and through college, would get them on his arms and upper body.)
So, how can you tell if the itching is due to exercise-induced urticaria, or just to your body simply adapting to running? The hives with exercise are a big clue, especially if you also develop hives in other situations, like in times of emotional stress or when eating spicy foods, says Pien. That’s because exercise-induced urticaria is part of a bucket of other hive-triggering skin conditions. (This includes cold urticaria, which may be a cause of itchiness that occurs in the winter, whether or not you’re exercising.)
Another factor: You start to itch well after your body’s acclimated to running. Itchiness caused by the physiological adaptation of your blood vessels should only last a few weeks, says Burns. But you can develop exercise-induced urticaria at any time, even if you’ve been running for years without a problem, says Pien.
If you think your signs point to exercise-induced urticaria, it’s important to see your doctor or allergist. Your doctor will want to make sure you’re not suffering from a similar—but much rarer and more serious—condition called exercise-induced anaphylaxis, which can cause dizziness, stomach distress, and wooziness along with the itching and hives, says Pien.
How can you prevent itchy legs while running?
If you’re just dealing with an itchy feeling—no hives or any of the red flag symptoms mentioned above—and just started running in the last few weeks, it’s probably just due to that physiological adaptation, says Burns. The good news is, chances are pretty high that it’ll peter out soon. The bad news is, there’s really nothing you can do to make it better in the meantime.
“It’s one of those things, you can think of it almost as a growing pain,” Burns says. “It’s a necessary discomfort of adapting to a new stronger, more aerobic body.”
You can try some troubleshooting to see if some apparel changes—say, loose shorts instead of tight compression pants, or vice versa—or post-workout habits (like a hot shower versus a cold shower) make the itching feel better for you, Burns says, but it won’t change the adaptation that’s going on in your body.
“My suspicion is, by the time you figured out any of the trends or things that can make it better, the itching would probably have gone away,” he says.
One thing you can do to stop it from happening again is to keep running, says Burns. The itching can start again if you resume running after a few months off, though it’ll likely persist for a shorter amount of time. “Our bodies do have a bit of memory, so that building back into it is going to be less rough than starting completely new from the first time.”
If you have itchy legs while running due to exercise-induced urticaria, you have a few options for prevention, says Pien. First, pay close attention to the kinds of exercise that trigger the itching. It might be that a slow, easy jog is OK, but a high-intensity sprint session isn’t. Your doctor may also recommend that you take an antihistamine before exercise that you suspect might trigger it. You can also tamp down the itching by taking an antihistamine after exercise if you forgot to do so before, says Pien. (Just make sure you talk with your doctor before you do so.)