Food reactions overview


IMPORTANT The information provided is of a general nature and should not be used as a substitute for professional advice. If you think you may suffer from an allergic or other disease that requires attention, you should discuss it with your family doctor. The content of the information articles and all illustrations on this website remains the intellectual property of Dr Raymond Mullins and cannot be reproduced without written permission.


Conditions such as eczema, vomiting, sloppy poos and irritability are very common in babies and infants. Most are not due to allergic or other reactions to food, but some are. This article provides an overview, with an emphasis on babies and infants with possible food reactions.

Allergic reactions to food: overview

“Immediate” (rapid onset) allergic reactions to food affect around 1 in 30 infants, and are relatively easy to diagnose. Symptoms of hives or vomiting usually occur within an hour or less after eating, and allergy testing is almost always positive.

Occasional children, however, do NOT have reactions that occur quickly. Instead, delayed immune reactions start after several hours or days, most commonly in response to dairy products, soy or wheat. Patients generally present with one or more of severe atopic dermatitis/eczema, chronic diarrhoea, failure to thrive, or severe reflux of food or formula. Symptoms occur due to inflammation of the skin or gut, and results from attraction of white cells from the blood into the tissues.

Routine allergy testing is often negative, making diagnosis more difficult. Diagnosis usually rests on the history of possible reactions to food, and responses to food withdrawal and re-challenge. Most of these delayed reactions resolve by the age of 3 years. At times, even small amounts of food allergen passing through breast milk can aggravate eczema or gut symptoms. Allergy testing of the infant may or may not be positive, depending on the mechanism of the sensitivity (immediate vs delayed).

Is food making me sick?

There are a number of potential explanations why symptoms may worsen after eating or drinking:


We eat often; therefore symptoms may worsen after a meal, even if the food is not the cause.

“Immediate allergy”

This is usually obvious, comes on very soon after exposure, and may trigger hives, vomiting or difficulty breathing. This form of allergy is most common in young children, is associated with positive allergy tests, and the most common triggers are egg, dairy, peanut, tree nuts and sometimes soy, wheat, seeds or seafood.

Delayed immune reactions to food

This is much less common, and almost always resolves by the age of 2-3 years. Symptoms are more subtle, may start a few hours to a few days after exposure, and allergy testing is usually negative. The most common triggers are dairy, soy and wheat, although sometimes other foods may be the cause. The most common symptoms are one or more of:

•severe eczema/dermatitis,

•severe and frequent vomiting or diarrhoea,


•failure to put on weight, and sometimes

•blood loss from the bowel.

Unfortunately, many of these symptoms may occur in non-allergic children, or in those with anatomical blockages in the bowel, making it hard at times, to diagnose.

Lactose intolerance

Results in stomach/gut upset only (eg, bloating, nausea, diarrhoea), not eczema. This is due to a partial enzyme deficiency (“lactase”), so that lactose-containing dairy products are poorly tolerated. Lactose-free milk causes no problems, and cheese and yoghurt are usually better tolerated than milk. This may be a permanent inherited condition, or can occur temporarily in a child after a bout of gastroenteritis, in which the lining of the bowel that produces lactase, is temporarily damaged.

How to tell the difference between lactose intolerance and cows milk protein allergy?

In lactose intolerance, lactose-free milk will be tolerated, and small amounts of cheese and yoghurt usually are too. When the problem is with cows milk protein, all forms of dairy, with or without lactose, will all cause problems.

Celiac disease

Occurs in around 1/300 people, results in inflammation of the bowel after exposure to wheat and gluten in the diet, and may cause one or more of diarrhoea, weight loss, poor absorption of nutrients or fatigue and lethargy. This does involve the immune system, but allergy testing is negative, as another arm of the immune system is involved. It is important to note that many people get bloated if they have too much bread or pasta, but most do NOT have celiac disease.

Food Intolerance

Food is composed of proteins, fat, carbohydrates and other nutrients. Most foods contain small amounts of naturally-occurring organic molecules (“food chemicals”) such as salicylates, amines and MSG-like glutamates. Sometimes these natural “building blocks” of food will aggravate skin or gut symptoms. Unfortunately, allergy testing is of no use, the history is not always reliable, and diagnosis rests on a temporary “elimination diet” under the supervision of a skilled dietitian, followed by “challenge” if it proves to be effective.

Food Aversion

“You just don’t like it”. This might be associated with unpleasant physical or emotional reactions in the past, such as severe food-poisoning after a certain food, followed later by sickness in the stomach at the very thought of eating it again, or its smell.


There are a number of other conditions that can mimic food allergic reactions. When these are suspected, additional tests may be required. Fructose intolerance is another enzyme deficiency, but this time it is “fruit sugar” that cannot be digested. Sometimes called “toddler’s diarrhoea” it can also occur in adults. Avoiding some fruits and juices can settle down gut symptoms quite quickly.

Principles of diagnosing food allergy


A suspicion is raised by the patient/parent. They are either right or wrong. If right, then one needs to decide how food is influencing their symptoms. One can try to confirm initial suspicions by:


Allergy testing is only of use when food reactions are of rapid (“immediate”) onset. Negative allergy tests do not exclude delayed immune reactions to food. In children with severe gut symptoms, sometimes a closer examination of the bowel may be needed. Blood tests are sometimes useful as well, particularly when trying to assess whether the child is absorbing nutrients.

Diet manipulation

At times, it may be important to prove or disprove whether food is causing the problem, or making it worse. This may involve temporary dietary restrictions to remove the implicated food, followed at times, by re-challenge.

Eczema and food allergy

Most infants with food allergy (~ 1/30 infants) have eczema (~1/5 infants), BUT most infants with eczema do NOT have food allergy! Food allergy does not cause eczema, but can worsen it in some very young children. As described above, food allergy is very common in young children in the first few years of life. The most common causes are cows milk/dairy, soy, hen eggs, nuts, seeds, wheat and seafood. When patients are allergic to a food, it is usually very obvious. The majority will get intensely itchy with large hives within an hour or less of eating. Scratching the hives makes the eczema worse. Occasionally, babies will be sufficiently allergic to a food to react to small amounts passing into breast milk. The history can usually be confirmed with allergy testing, even in very young children. Most food allergies that aggravate eczema will disappear within the first 2-3 years of life. Even though taking young children off wheat and milk is often almost seen as “routine” treatment for eczema in some quarters, it does not work in the majority. Long-term unsupervised (and often unnecessary) dietary restriction (sometimes advocated by alternative practitioners) can also lead to malnutrition.

Food allergy and the gut

There are many causes of vomiting and stomach upset other than food allergy, including enzyme deficiencies, anatomical abnormalities or non-allergic inflammatory conditions. affecting the gut. Investigation by a stomach specialist (gastroenterologist) may also be required.

Management of food allergy

Since "desensitisation" to switch off food allergy is till in the research basket for now (despite promising early results), the management of food allergy in children involves avoidance, re-evaluation from time to time to determine whether the allergy has resolved, education of parents and care-givers about food allergy, sometimes deliberate re-challenge with the food (when it is considered safe to do so), and the development of an individual Action Plan in case accidental exposure occurs, of particular importance where reactions are of rapid onset and severe.

Nutritional issues

Child: infant formula is most important in the first 12-18 months of life, as a source of protein, fat, calcium and other nutrients. As the child ages, more nutrition is obtained from solids, leaving formula as an important source of calcium, but not the only one. Sources of calcium include dairy products, soy, calcium fortified rice milk, and dietary supplements. If a child’s diet needs to be restricted excessively, review by an experienced allergy dietitian may be recommended.

Mother: where a breast-feeding mother’s diet needs to be restricted because her child is allergic to some foods, dietary supplements may be needed. When there is evidence that a child is allergic to many foods, it may be easier to wean a child onto a formula and stop breast-feeding. Again, review by an experienced allergy dietitian may be required.

Infant formulae and food allergy

Regardless of type, infant formulae are designed to be an excellent source of nutrition.  Most use cows milk or soy as the source of protein. When children are allergic to one of more of these, “special” formulae can be used.  This might involve substituting a soy formula in a child with cows milk allergy alone, use of specially treated cows milk formula (such as PeptiJunior), or use of “elemental  formula” such as Neocate or Elecare, in which there are no intact proteins for the immune system to recognise. These may not taste as good as breast milk or even “ordinary” formula, but perseverance, and sometimes the use of flavours like vanilla essence or a small amount of Golden Syrup, may make them more palatable. These formulae are very expensive, need an Authority prescription for a PBS subsidy in Australia, and are only approved for subsidised use in Australian patients with combined cows milk and soy allergy under certain conditions.

Last reviewed 28 January 2010