Food allergy and eczema: what the evidence says

If your child has eczema, someone has probably asked you what they’re eating. It’s a natural question: eczema and food allergy really do show up in the same children. But the link isn’t what most people assume, and acting on the wrong idea can cause harm. Here’s what the evidence says about which comes first, why cutting foods out is risky, and what Canadian paediatricians now recommend.

Why do eczema and food allergy go together?

They share a root. Both are part of the “atopic” tendency, an inherited readiness of the immune system to overreact. And the Canadian Paediatric Society is clear that the infants most at risk of developing food allergy are those who already have eczema or another food allergy.

The British Association of Dermatologists explains the order of events: in most children, eczema comes before food allergy, not the other way round. Eczema that starts early and is more severe is linked with a higher chance of food allergy.

A leading explanation involves the skin barrier (the outer layer that keeps water in and irritants out). When eczema leaves that barrier leaky, tiny food particles from the environment can get into the skin more easily, and the immune system may learn to treat them as a threat. The British Association of Dermatologists describes this as eczema making it easier for food proteins to get into the skin and set off an allergic response. Meanwhile, eating a food regularly seems to teach the immune system to tolerate it. That’s the thinking behind current Canadian advice on introducing foods, below.

Does food cause eczema?

For the large majority of children, no. The British Association of Dermatologists states that food allergies don’t cause eczema, even though the two often go together.

That doesn’t mean food never matters. Some children have a real food allergy alongside their eczema, and in a smaller group a food can make eczema flare. It helps to know the two kinds of reaction:

• Immediate reactions happen within minutes of eating and up to a few hours afterwards: hives, swelling, vomiting, or in serious cases trouble breathing.
• Delayed reactions can show up within a day or two as an eczema flare or tummy symptoms, which makes them much harder to link to one food.

An immediate reaction is a reason to see a doctor, and any reaction with breathing trouble or swelling of the lips, tongue or throat is an emergency: call 911.

Why is cutting out foods risky?

It seems harmless to “just try” removing milk or egg. The evidence says it isn’t that simple.

It rarely helps much. A 2022 systematic review and meta-analysis pooled 10 randomized trials with 599 participants, whose median age was a year and a half. About 50% of those on an elimination diet improved meaningfully, compared with 41% of those who weren’t. The authors rated the evidence low certainty and described the benefit as slight and possibly unimportant.

It can create a more dangerous allergy. A US study followed children referred to an allergy clinic for eczema thought to be triggered by food. Among those with follow-up, 19% who had never had an immediate reaction developed one, and about 30% of the new reactions were anaphylaxis (a severe, whole-body allergic reaction). Most new reactions happened to foods the children had been avoiding, most often milk, egg and peanut. The authors concluded that strict elimination diets should be prescribed cautiously because avoidance may reduce the body’s tolerance. This was one clinic’s records, not a trial, but it matches what the British Association of Dermatologists warns: excluding foods without good reason can increase the risk of severe immediate reactions.

It can affect growth and nutrition. Growing children need a varied diet, and unsupervised elimination diets risk nutrient gaps, the same society notes.

It can delay treatment that works. The 2022 review’s authors pointed to the risk of withholding more effective eczema treatment while families focus on diet.

What about allergy tests?

Tests can mislead in children with eczema. The American Academy of Dermatology explains that a positive skin or blood test needs to be confirmed, often with a food challenge (eating the food in small steps under medical supervision), before anyone concludes a child is allergic. A positive test shows the immune system recognizes the food, not that eating it causes a reaction.

The Canadian Paediatric Society advises against screening babies for food allergy before introducing foods. The American Academy of Dermatology suggests talking about testing when eczema doesn’t improve after a few weeks on the care plan, when flares consistently follow a specific food, or when a child isn’t growing as expected. The British Association of Dermatologists recommends only validated tests, done and interpreted by professionals, so it’s best to skip tests sold directly to parents.

What does Canadian advice say about introducing foods?

This is the part that has changed most in recent years, and it’s good news. The Canadian Paediatric Society’s 2021 position statement defines a high-risk infant as one with eczema or another allergic condition, or with a parent or sibling who has one. For those babies, it recommends:

• introducing common allergenic foods, such as cooked (not raw) egg and peanut, at about six months and not before four months, in a safe, age-appropriate form, at home
• once a food is in, keeping it in the diet regularly, a few times a week, to maintain tolerance
• no routine allergy testing beforehand; the society notes that the risk of a severe reaction on first exposure is extremely low

It also found not enough evidence to recommend changing a parent’s diet during pregnancy or breastfeeding to prevent food allergy. If your baby has severe eczema, has already reacted to a food, or you’re anxious about getting started, ask your doctor to help you make a plan.

When should you see a doctor or allergist?

• Your child has had hives, swelling or vomiting soon after eating a food.
• Flares consistently follow one particular food.
• Eczema isn’t improving despite a few weeks of good skin care.
• Your child isn’t growing as expected, or you’re already avoiding several foods.
• You’d like support introducing allergenic foods to a high-risk baby.

Eczema and food allergy are relatives, not cause and effect: in most children the leaky skin of eczema comes first. Cutting foods out on your own rarely clears the skin and can make a real allergy more likely, while early, regular introduction of foods like egg and peanut helps protect babies at risk. Keep treating the skin, keep food varied, and bring any food worries to your doctor rather than the grocery list.