Don't let hives stop you from exercising

Q: What's the best way to treat exercise-induced hives? Is this a condition that will eventually just go away? I get hives every day when I work out if I don't take an over-the-counter antihistamine.

A: Some people get hives (urticaria) after exercise. Hives that appear after exercise can occur with or without other allergy symptoms.

If exercise causes large hives (usually a centimeter or more in diameter) along with throat swelling or lightheadedness, nausea or headaches, you may have a condition named 'exercise-induced anaphylaxis.'

If exercise causes smaller hives (usually less than a half- centimeter), you're more likely to have a condition called 'cholinergic urticaria.' Either of these problems can be accompanied by wheezing with breathing (asthma).

Exercise-induced anaphylaxis is frequently triggered by a food allergy. The way that food allergy can relate to exercise is still debated. Some experts believe that exercise changes your digestion and food absorption, so exercise after eating leads you to have a greater exposure to food proteins that cause allergy.

Many people with exercise-induced anaphylaxis notice that they will not have hives after exercising if they have had an empty stomach for six to eight hours before exercising, or if they avoid specific foods for 24 hours before exercising.

The most common food allergy that triggers exercise-induced anaphylaxis is wheat allergy. Allergy to nuts, shellfish, eggs and other foods can also cause this problem. A person with hives after exercise should consider getting tested for food allergies. Once your triggers are known, you should avoid exercising after eating food allergy triggers.

Full-blown symptoms of anaphylaxis can be dangerous. If you have other allergy symptoms with your hives, you should exercise with a partner and carry epinephrine that can be injected (such as the Epi-pen). Antihistamines (particularly hydroxyzine) may help symptoms, but they may not prevent a severe attack.

Cholinergic urticaria is also known as heat-induced urticaria. This kind of hives from exercise is a reaction that can occur from a warm body temperature or from sweating. If you have this kind of hives, you may also notice hives after taking hot showers, after getting emotional or after eating hot foods. If this is your hive problem, an antihistamine such as hydroxyzine (Atarax) is helpful before exercise, and it can also be helpful for you to avoid exercising in hot weather.

For most people who get hives after exercise, this is a long-term problem.

If a food allergy is identified as a trigger, symptoms can likely be avoided if you don't exercise after eating, or if you change your diet to eliminate the allergen.

Information from Mary Pickett, associate professor of medicine at Oregon Health and Science University. For additional consumer health information, visit health.harvard.edu.