Food allergies - what they are and how they can affect you

Food allergy is a reaction to a food protein. The most common proteins (allergens) that trigger reactions are those found in cow's milk, eggs, peanuts, wheat, soy, fish, shellfish and tree nuts.

The reaction is usually immediate – from a few seconds to two hours after you eat. However, in some types of food allergy, reactions are delayed. Allergic reactions vary and range from mild, such as a skin rash, to a fast, life-threatening reaction (anaphylaxis).

People with food allergies develop symptoms when eating foods that are part of most people's healthy diet. Even small amounts of the offending food can cause serious reactions in susceptible individuals.

Food allergy is relatively common in children, but many children grow out of their allergies by adulthood. Food allergy affects up to 4% of children and up to 2% of adults. The tendency to allergy usually runs in families. The only way for allergic individuals to manage a food allergy is to avoid eating the food that causes it.

Symptoms of food allergy

The symptoms of food allergy range from mild discomfort to severe or life-threatening reactions requiring immediate medical attention. Symptoms include:

  • Skin: hives, eczema, swelling, itching
  • Respiratory: sneezing, asthma, difficulty breathing, cough
  • Gastrointestinal: swelling and itching of the lips and mouth, vomiting, reflux, colic, diarrhoea, cramps, constipation
  • Circulation: low blood pressure, dizziness, anaphylactic shock.

While around 160 foods can cause food allergies, there are eight, which are responsible for 90% of allergic reactions to foods. These are egg, milk, peanut, soy, fish, seafood, wheat, and tree nuts.

A food that causes an allergy is called an allergen. Allergens will affect a food-allergic person every time they eat it. For some people, only a tiny trace can trigger a reaction.

How allergies are identified

Your doctor or specialist will want your reaction history and will probably do a physical examination. There are also tests to help identify a food allergy.

During a skin prick test, small drops of the potential allergens are placed on your arm (or back for a small child). A tiny prick is then made in the skin so the allergens come into contact with tissue. A red and raised area will develop around the drop you are allergic to. Skin prick tests do not work if you are taking anti-histamines or using steroid creams. You will need to stop these several days before the test. Skin prick tests are not suitable if you have severe eczema, a severe peanut allergy (if suspected) or for distressed infants.

Another option is radioallergosorbent testing (RAST). This blood test checks for reaction to the eight major food allergens. You can have this test done while using antihistamines and steroid creams. There is also no risk of severe allergic reaction as your blood is taken away and analysed. Note though that a positive test result does not always mean an allergy.

If you, or your child, are diagnosed with a food allergy you need to avoid all sources of that food. Research suggests children have a better chance of growing out of a food allergy if they completely avoid the food. To find out whether you are still allergic or have grown out of an allergy, you can be re-tested.

In cases where the allergy is severe, you might need to wear a Medic Alert bracelet and carry special medication such as antihistamines or an auto-injector such as an Epi-Pen®. You should discuss this with your doctor.

Egg and milk allergies are the most common food allergies among infants but are often outgrown. Shellfish allergy is more common among adults than children. Peanut allergy is equally common among children and adults. When eliminating food groups from your diet, the supervision of a dietician is highly recommended.

The Ministry of Health has a range of publications about nutrition. Contact your doctor or local Public Health Unit (look in the White Pages under 'Public Health') or click on the link below.

Food and nutrition guidelines (External website)

How to minimise the risk of your baby having food allergies

Your baby is more likely to develop an allergy if you have a family history of food allergies. For example if both parents have an allergy or one parent and a sibling with allergy.

While you are pregnant and breastfeeding it is suggested that you avoid peanuts and peanut butter. Breastfeeding may be protective and, if you can, delay the introduction of solids until the baby is six months old. Avoid introducing cow's milk, egg, and fish until age one, and peanuts, nuts and shellfish until age three.

Food intolerance - what it is and how it can affect you

Food intolerance covers all other food-related reactions, generally those that cannot be tested for.

Where can I get more help?

Your health professional

  • Your GP or local medical centre
  • Allergy specialist or paediatrician - this requires a referral from your GP unless you are in Auckland or Christchurch where there are private allergy specialists
  • Dietician - a hospital dietician requires a referral from your GP, or look for a private dietician.