How ‘co-factors’ can increase the likelihood of a food allergy reaction

Food allergies are complex things, and people don’t react the same way to their allergy trigger every time they encounter it, experts say.

“Co-factors” like hard exercise or certain medications can alter how someone responds to an allergen, lowering the threshold at which they react, said Dr. Anne Ellis, professor and chair of the Division of Allergy and Immunology at Queen’s University.

Sometimes this can be full-on anaphylaxis, such as a case reported by the Daily Mail, where a woman said she had a severe reaction when she combined fish and wine in a meal — despite having consumed both independently without incident in the past.

A case involving two foods would be extremely unusual, said Dr. Harold Kim, president of the Canadian Society of Allergy and Clinical Immunology, and an associate professor at Western University.

“It would be very unlikely that it’s an actual allergic reaction to the wine,” Kim said. “It’s just that the wine is potentiating the reaction to fish.”

There are well-known factors that can make people more sensitive to allergy triggers, and alcohol is among them.

“One of the most classic examples that we see quite frequently is what we call food-dependent exercise-induced anaphylaxis,” Ellis said.

“You can eat the food and be fine. You can exercise and be fine. But if you exercise within two hours of eating your trigger food, you’ll have anaphylaxis.”

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Alcohol and anti-inflammatory medications, like ibuprofen, are frequent triggers, Ellis said. Illness and fever can also have a similar effect.

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The most common food allergies that are triggered by a co-factor are wheat, celery and seafood, Kim said. The reaction can range from mild, like hives, to something that requires an emergency room visit.

And co-factors usually affect younger people.

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“It often affects young, healthy patients, often young athletic females that run and eat a salad or some carbohydrate-based food before they run,” he said. “That’s kind of the classic situation.”

It would be unusual for this reaction to come as a complete surprise, Ellis said. Usually it would appear in people who have a known food allergy, who just became more sensitive.

“For the most part, food allergies aren’t hidden. They aren’t subtle. And usually the story is quite consistent.”

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Doctors aren’t quite sure what happens to change someone’s reaction to a food, but suspect it has to do with increased bloodflow and changes to how allergens are absorbed.

People have thresholds for their allergies, Ellis said, with some people not reacting unless they’ve had nine peanuts, but are fine with a fraction of a peanut.

Exercise and alcohol can dilate the blood vessels, she said, making people more likely to absorb the antigen, and develop symptoms at a lower dose.

Most people with food allergies react the same way to their trigger every time. Only a few have co-factors to their allergies — Kim estimates that he sees approximately one such patient per month. “It’s a strange phenomenon,” he said.

If someone reacts once to the combination of exercise and an allergy trigger, it’s likely they will react the same way again, Kim said.

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Ellis recommends that people with food allergies be aware of the possibility of a co-factor, and avoid situations that combine their risks.

“It’s just perhaps something to have in the back of your mind, if you do have a food allergy,” Ellis said, “to be extra-cautious if you’re going to be consuming alcohol, or at times when you’re sick, or if you’re taking certain anti-inflammatories, that these are all things that could potentially lower your threshold.”

Allergists are trained to ask about things like alcohol when they assess an allergy, she said, and should be able to tell you if this might be a factor. And severe allergic reactions should always be checked out by a medical professional.

“If you do have a significant reaction, where you’re having more than just hives and flushing, make sure that you’re presenting yourself to emergency care and not just taking your own antihistamines.”