Welcome back to Just Curious, Strong Women’s weekly series exploring all the random health and fitness questions you’ve always wondered about but never got the answers to.

This week, we’re exploring why some people experience an allergy-like reaction after a workout, and whether there’s anything you can do about it.

Whether you go bright red in the face, end up dripping with sweat, feel a little bit nauseous or a combination of all three, the aftermath of an intense workout can be a lot. Pushing your body to run faster or lift heavier can take a lot of effort, so it’s hardly surprising that you’re left feeling a little depleted afterwards.

But for some people, the side effects of working out don’t stop there. Itchiness is one symptom that can arise, either in the form of some light scratchiness or full-on hives.

If you’ve ever found yourself scratching at your legs after a run or noticed a rash appear on your arm after a HIIT class, you’ll know what we’re talking about. But what causes this post-exercise itchiness? And is there anything you can do about it?

To get to the bottom of the issue, we asked Professor Michael Rudenko, a consultant in allergy and immunology at HCA Healthcare’s Chiswick Medical Centre, and Dr Sophie Momen, consultant dermatologist at One Welbeck Skin Health & Allergy, for their take. 

There are several reasons why you might develop itchy skin after a workout – the first simply being increased blood flow to the skin.

When we work out, our heart rate increases to push more blood around the body. This increase in blood flow is important because it helps to ensure our muscles have plenty of oxygen-rich blood to fuel them, but it also helps to keep the body cool: as our body temperature decreases our blood vessels dilate and pushes blood flow closer to the surface of the skin, where it’s cooler.

And it’s this push of the blood towards the skin’s surface that can contribute to an itchy sensation. “The blood flows into smaller blood vessels called capillaries, which sit close to the skin and to nerve endings,” Dr Momen explains. “Chemical messengers may be released from these nerve endings, which we then perceive as an itching sensation.”

However, in some cases, this post-workout itchiness can become more serious, due to a condition known as exercise-induced urticaria.

The condition, which is estimated to affect around 5-20% of people, occurs due to a release of histamine – a chemical released by the body’s immune system.

“Exercise-induced urticaria is a condition that results in rashes and potentially swelling associated with exposure to co-factors, such as exercise,” Professor Rudenko explains.

It’s known as exercise-induced urticaria because it’s thought to occur in response to sweating – so exercise is one of the most common triggers. Other potential triggers include warm temperatures, hot baths, spicy foods and emotional stress – anything that sets your sweat mechanisms into action.

Some people also find that it’s triggered when they exercise in the cold and then come inside as the skin warms rapidly.

“The exact cause of exercise urticaria is unknown but it is thought that in response to sweat, the nervous system releases a chemical messenger called acetyl choline from the nerves in your skin,” Dr Momen adds. “This causes the skin to feel irritated and an allergic reaction occurs, the result of which is hives and swelling.”

Other reported symptoms of exercise-induced urticaria include skin flushing or redness, stomach cramps and swelling. In serious cases, it can lead to anaphylaxis.

In rare cases, exercise-induced urticaria can be linked to the consumption of wheat and gluten. Also known as ‘exercise-induced wheat-related urticaria’, this condition is diagnosed when patients get symptoms after doing exercise only when they’ve eaten gluten beforehand.  

If your skin gets a little itchy every once in a while when you workout, it’s probably not anything to worry about. However, if you develop symptoms of an allergic reaction – like hives or swelling – then it’s important to seek help.

“Exercise-induced urticaria requires medical attention as it can be quite significant,” Professor Rudenko says. “There are certain diagnostic tests that can be run that, together with a detailed medical history, can help to diagnose and treat this condition.”

Treatments for exercise-induced urticaria may include antihistamines, as well as other medications used to treat asthma and acid-reflux.

You may also need to make lifestyle changes to reduce your risk of a flare-up. These changes may include:

• Exercising in cooler environments (e.g. late evening or air-conditioned rooms)
• Avoiding very hot showers and baths
• Finding ways to manage and reduce stress (e.g. meditation or seeking professional advice) 

Images: Getty