Do allergic reactions get worse each time? New evidence

Do allergic reactions get worse each time? It's one of the first questions parents ask after a reaction, usually followed by the hope that a mild one means a mild allergy. A study presented at the Canadian Society of Allergy and Clinical Immunology (CSACI) meeting in Toronto in October 2026 gives a clear answer: not necessarily worse, but not predictable either. In children who had anaphylaxis twice to the same food, how severe the first reaction was said almost nothing about how severe the second would be.

Do allergic reactions get worse? What the study found

Researchers at McGill University looked at 140 children treated at the Montreal Children's Hospital emergency department between 2011 and 2024 who had anaphylaxis at least twice to the same food: 280 reactions in all. The children were part of the Cross-Canada Anaphylaxis Registry (C-CARE). Each reaction was graded mild, moderate or severe, checked by two team members and confirmed by an allergist.

• 57.8% had a second reaction of the same severity as the first.
• 22.9%, nearly one in four, had a more severe second reaction.
• 19.3% had a less severe one.

Statistically, the severity of the first reaction didn't predict the second (weighted kappa 0.13, which means no meaningful agreement). The symptoms were just as unpredictable: for each body system (the skin, breathing, the stomach, and the heart and circulation), whether it was involved the first time didn't predict whether it would be involved the second time.

When the first reaction was mild

This is the part parents most need to hear. Of the 38 children whose first reaction was graded mild, 23 had a moderate second reaction and 4 had a severe one. That's 27 of 38, about 7 in 10, whose next reaction was worse than their first.

A note on the word "mild": every reaction in this study was anaphylaxis, meaning it involved at least two body systems or a drop in blood pressure. "Mild" was the lowest of three grades of anaphylaxis, not a few hives.

The children in the study

• Median age at the first reaction: 4.7 years
• Boys: 60.7%
• Median time between the two reactions: 17 months
• History of asthma: 21.4%
• Food triggers: peanut 31.4%, milk 22.1%, tree nuts 20.0%, egg 10.7%, other foods 15.8%

What the researchers recommend

The poster's clinical message was blunt: counsel on recognition, not reassurance. In practice:

• A mild history isn't reliable. Don't let a mild first reaction set expectations for the next one.
• Every child with food-induced anaphylaxis needs to be ready: epinephrine on hand, an action plan, and caregivers trained to act early.
• Treat any reaction that involves the whole body promptly, whatever happened last time.

The authors also point to a gap: only about half of children with food allergies carry an unexpired auto-injector, and in past studies of adolescents the figure was 23 to 38%.

What this means at home, at school and on the road

1. Carry two doses every time, even if every reaction so far has been mild. See how many epinephrine doses you should carry.
2. Follow the plan, not the history. Your child's signed anaphylaxis emergency plan says which signs mean "give epinephrine now". Use it the same way for every reaction.
3. Brief every adult. Grandparents, coaches and sitters should know the signs and where the epinephrine is. Our anaphylaxis emergency plan guide covers what to write down.
4. Keep devices in date and in range, so the one in the bag works when it's needed.

Where ResQBand fits

A plan only helps if the adult beside your child can find it and follow it. The ResQBand Tap Card keeps the instructions with the epinephrine. The card itself is printed "Use immediately" and "Call 911". Tapped with most phones, it opens your child's emergency page with the use instructions, a Call 911 button, and a button the helper can press to text you and your other emergency contacts who opted in, with the helper's location when their phone shares it. Alerts are free once the card is registered, with no subscription.

About the study

Severity Patterns in Recurrent Anaphylaxis to the Same Food Trigger was presented at the 81st CSACI Annual Scientific Meeting in Toronto by Joseph Najem and colleagues from McGill University, with co-authors from centres across Canada, including Memorial University in St. John's, and senior author Moshe Ben-Shoshan. The authors note its limits: the data come from one emergency department, so milder reactions managed at home may be missing, and 140 pairs of reactions is a modest sample. Next, they plan to look at co-factors such as exercise, infections and the amount eaten. Poster results are early findings.

The short version

Allergic reactions don't reliably get worse each time, but they don't reliably stay the same either. Nearly one in four children in this study had a worse second reaction, so prepare for every reaction as if it could be serious.

This article summarises research for general information. It isn't medical advice: follow your emergency plan. In an emergency, call 911.