Why Are Food Allergies Suddenly So Much More Common?

Food allergies have roughly doubled in prevalence over the past two to three decades in many high-income countries, and researchers still don’t have a single clean explanation for why. The leading theories point to changes in how infants are introduced to food, shifts in the gut microbiome, vitamin D levels, and modern hygiene practices — likely several factors working together rather than one culprit. What’s clear is that the rise is real and measured, not just better reporting of something that was always there.

Why Are Food Allergies Suddenly So Much More Common?

The increase is real. Researchers have tracked it through medical records, emergency department visits, and population surveys across multiple countries, and the pattern holds up even when accounting for better diagnosis and greater awareness.

What changed isn’t human biology in any fundamental sense. What changed is the environment infants and children grow up in. Their immune systems develop differently than they did a few generations ago, and the result is that more of them mistakenly flag harmless food proteins as threats.

Several explanations have real supporting evidence. None of them fully explains the rise on its own. Most researchers now think the answer involves multiple factors interacting — which is part of why the question has been so hard to answer definitively.

What Actually Happens in the Body During an Allergic Reaction to Food?

A food allergy is an immune system response, not a digestive problem. The immune system identifies a specific protein in a food as dangerous and produces antibodies called immunoglobulin E, or IgE, against it.

Those IgE antibodies attach to mast cells, which are immune cells found throughout the body, especially in the skin, airways, and digestive tract. The first exposure usually causes no symptoms — it just sensitizes the system. On a later exposure, the food protein binds to the IgE on those mast cells and triggers them to release histamine and other chemical mediators.

That release is what produces symptoms: hives, swelling, vomiting, difficulty breathing, a drop in blood pressure. Symptoms typically begin within minutes to two hours of eating the trigger food. Reactions can vary in severity from one episode to the next, and a prior mild reaction does not guarantee future reactions will also be mild.

This is different from food intolerance, which does not involve IgE or the immune system in this way. Lactose intolerance, for example, is a digestive issue caused by low levels of the enzyme lactase. It can cause discomfort but does not cause anaphylaxis.

What Is the Hygiene Hypothesis and Does It Hold Up?

The hygiene hypothesis proposes that modern living — cleaner environments, smaller families, less exposure to microbes early in life — leaves the developing immune system without enough practice distinguishing real threats from harmless ones. The idea has evolved since it was first proposed, and researchers now often refer to it as the “microbiome hypothesis” or “old friends hypothesis.”

The evidence is suggestive but not conclusive. Children raised on farms, particularly those exposed to livestock and farm dust, tend to have lower rates of allergy and asthma in observational studies. Children with more siblings also tend to have somewhat lower rates. But these are associations, and observational research cannot prove cause and effect.

What has become clearer is that the gut microbiome — the community of bacteria and other organisms living in the digestive tract — plays a role in training the immune system. Infants with less diverse gut bacteria in early life appear more likely to develop allergies later. How to translate that into prevention is still an open question. Probiotic supplements have been studied for allergy prevention, and results have been mixed. No specific probiotic strain or dose is currently established as reliably preventive.

Did Changes in Infant Feeding Advice Make Things Worse?

For years, major health organizations recommended delaying the introduction of common allergenic foods — peanut, egg, milk, wheat, soy — until children were older. The reasoning seemed sensible: avoid the food, avoid the allergy. It turned out to be wrong.

That guidance was largely withdrawn after a landmark clinical trial showed the opposite. The LEAP trial, published in the New England Journal of Medicine in 2015, found that introducing peanut products to high-risk infants between 4 and 11 months of age dramatically reduced their risk of developing peanut allergy compared with avoiding peanut. The effect was strong enough that it changed infant feeding guidance in the United States and several other countries.

Current guidance from major pediatric and allergy organizations generally recommends introducing allergenic foods — including peanut and egg — around 6 months of age, alongside other solid foods, rather than delaying them. For infants at high risk of allergy, such as those with severe eczema or an existing egg allergy, many clinicians recommend evaluation before introduction, since early introduction in that group carries its own considerations.

This is one of the more concrete findings in the field. The timing of introduction matters, and the earlier advice likely contributed to the rise.

Is Vitamin D Deficiency Part of the Picture?

Vitamin D plays a role in regulating the immune system, and low levels have been associated with higher rates of food allergy in some studies. The geographic pattern is one reason researchers looked: children living farther from the equator, where sunlight exposure is lower, tend to have higher rates of food allergy and epinephrine prescriptions.

The association is consistent but the evidence for causation is weak. Supplementing with vitamin D has not been shown in large trials to prevent food allergy. It’s plausible that vitamin D is one contributing factor among several, but it is not established as a primary cause, and it is not established as a preventive intervention.

Are Food Allergies Overdiagnosed or Underdiagnosed?

Both happen, and for different reasons.

Overdiagnosis is common when people rely on blood tests or skin prick tests alone. These tests detect sensitization — the presence of IgE antibodies — but sensitization does not always mean a person will react when they eat the food. Many people test positive to a food they eat regularly without any problem. A proper diagnosis requires a clear history of symptoms after eating the food, and in some cases an oral food challenge performed under medical supervision.

Underdiagnosis happens when reactions are attributed to something else, or when people avoid a food without ever getting evaluated. This can lead to unnecessary dietary restriction, which has its own nutritional costs, especially in children.

Accurate diagnosis matters because avoiding a food you’re not actually allergic to carries real downsides, and missing a true allergy carries serious risk.

How Common Are Food Allergies Now, and Which Foods Cause Most Reactions?

In the United States, roughly 6 to 8 percent of children and about 4 percent of adults are estimated to have a food allergy, based on survey and clinical data. The most common triggers vary somewhat by age.

• Peanut — one of the most common and most likely to cause severe reactions
• Tree nuts — walnut, almond, cashew, pistachio, and others
• Milk — most common in young children; often outgrown
• Egg — also common in children; often outgrown
• Wheat — distinct from celiac disease, which is not an allergy
• Soy — more common in infants and young children
• Fish and shellfish — more common in adults; usually lifelong
• Sesame — recognized as a major allergen in the U.S. as of 2023

Milk, egg, wheat, and soy allergies are more likely to be outgrown than peanut, tree nut, fish, and shellfish allergies, which tend to persist. This pattern is well documented, though individual outcomes vary.

Can Food Allergies Be Prevented?

Early introduction of allergenic foods is the most evidence-supported prevention strategy currently available, and it applies mainly to infants at higher risk. The LEAP trial demonstrated this clearly for peanut. Subsequent research has supported similar approaches for egg and other foods, though the evidence is strongest for peanut.

Other proposed prevention strategies — avoiding certain foods during pregnancy, delaying introduction, using probiotics, or taking vitamin D — have weaker or mixed evidence. Some clinicians recommend these approaches, but they are not established as reliably preventive.

For children who already have a food allergy, strict avoidance of the trigger food remains the standard approach. Injectable epinephrine is the first-line treatment for severe reactions and should be carried by anyone at risk of anaphylaxis. Antihistamines can help with mild symptoms but do not treat anaphylaxis.

Oral immunotherapy — gradually introducing small amounts of the allergen under medical supervision — has been studied and is used in some clinical settings. It can reduce sensitivity in some patients, but it carries risks including allergic reactions during treatment, and it is not a cure. Whether it leads to lasting tolerance in most patients is still being studied.