Food allergens are the leading cause of anaphylaxis, and in North America, Europe, and Australia, peanuts are the single most prevalent trigger. Peanuts and tree nuts together account for the majority of food-induced anaphylactic reactions in these regions, though the picture shifts depending on where in the world you live. Food allergies affect roughly 6% of U.S. adults and 8% of children, and anaphylaxis from these allergies sends tens of thousands of people to emergency departments every year.
Why Peanuts Top the List
Peanuts consistently rank as the most common food trigger for anaphylaxis in Western countries for a few reasons. Peanut proteins are unusually resistant to digestion and heat, meaning they survive cooking and stomach acid largely intact. This gives the immune system more opportunity to mount a reaction. Peanuts are also widespread in processed foods, making accidental exposure more likely than with other allergens.
The U.S. recognizes nine major food allergens: milk, eggs, fish, shellfish, tree nuts, peanuts, wheat, soybeans, and sesame. Together, these account for about 90% of all food-allergic reactions. But not all allergic reactions are anaphylaxis. Milk and egg allergies are extremely common in young children, for instance, yet they cause anaphylaxis less frequently than peanut and tree nut allergies do. The severity and unpredictability of peanut reactions are what set them apart.
The Trigger Changes by Region
What counts as the “most prevalent” allergen depends heavily on geography and diet. In Asia and Latin America, shellfish and seafood replace peanuts as the dominant cause of food-induced anaphylaxis. In Hong Kong, shrimp is the most common food triggering anaphylaxis in emergency departments. Some Asian countries also see allergic reactions to less familiar allergens like edible insects and bird’s nest.
This regional variation reflects what people eat most. Populations with high seafood consumption develop more seafood allergies, while populations where peanuts are a dietary staple see more peanut allergies. The underlying biology is the same, but the trigger shifts with the local food supply.
Non-Food Causes of Anaphylaxis
While food is the leading cause overall, two other categories of triggers are responsible for a significant share of anaphylactic reactions: insect venom and medications.
About 3% of adults and 0.8% of children will experience a severe systemic reaction to stings from honeybees, wasps, hornets, or yellow jackets at some point. Venom anaphylaxis is particularly dangerous because stings are hard to predict and often happen far from medical help. Among adults specifically, insect stings rival food as a cause of fatal anaphylaxis.
Medications are another major trigger, with antibiotics (particularly penicillin-type drugs) and certain pain relievers among the most common culprits. Reactions to medications can occur even if you’ve taken the same drug before without problems.
What Happens in Your Body During Anaphylaxis
Anaphylaxis is driven by a chain reaction in the immune system. When someone with an allergy encounters their trigger, their immune system has already produced antibodies primed to recognize that specific substance. On re-exposure, these antibodies activate mast cells, a type of immune cell packed with chemical signals. The mast cells essentially burst open, flooding the body with histamine and other inflammatory compounds within seconds to minutes.
These chemicals cause blood vessels to widen and leak fluid, which drops blood pressure rapidly. They also cause smooth muscles to contract, which is why the airways tighten and breathing becomes difficult. The reaction is systemic, meaning it affects the whole body at once, unlike a localized allergic reaction such as hives on one area of skin. This whole-body involvement is what makes anaphylaxis life-threatening.
How Common Anaphylaxis Really Is
Anaphylaxis is serious but relatively rare in absolute terms. Pediatric emergency department data from 2016 to 2022 showed over 42,000 visits for anaphylaxis in children during that period. Notably, the rate is climbing, with a 4.2% increase per year in visit incidence. Despite the severity of these episodes, the median hospitalization rate was only 3.5%, and repeat hospital visits were rare at 0.6%, suggesting most cases resolve with emergency treatment.
The upward trend tracks with the broader rise in food allergy diagnoses over the past two decades. More people with food allergies means more potential for anaphylactic reactions, even as awareness and preparedness have improved.
Biphasic Reactions: The Second Wave
One lesser-known risk of anaphylaxis is the biphasic reaction, where symptoms return hours after the initial episode appears to have resolved. Estimates of how often this happens vary widely, but a large U.S. food allergy registry study found a biphasic reaction rate of about 16%. Self-reporting adults in the study reported biphasic reactions at a higher rate (nearly 22%) than parents reporting on behalf of children (about 13%).
This second wave can be just as severe as the first. It’s the reason people who experience anaphylaxis are typically observed for several hours after treatment, even if they feel completely fine. The unpredictability of biphasic reactions also underscores why carrying two doses of epinephrine is standard advice for anyone with a known anaphylaxis risk.
Recognizing Anaphylaxis Early
Anaphylaxis typically involves two or more body systems at once. You might see skin changes like hives or flushing combined with difficulty breathing, a drop in blood pressure, or gastrointestinal symptoms like vomiting and cramping. The combination is key. A single symptom like hives alone is usually a milder allergic reaction, but hives plus throat tightness or dizziness signals something more dangerous.
Symptoms usually appear within minutes of exposure, though food-triggered reactions can sometimes take up to an hour as the allergen is digested. The faster symptoms develop, the more severe the reaction tends to be. Epinephrine is the only effective first-line treatment, and it works best when given early. Antihistamines can help with skin symptoms but do not reverse the airway constriction or blood pressure drop that make anaphylaxis fatal.