An update on allergies

With allergies seemingly on the increase, Dr Abby Baskett examines the latest research and advice for parents.

Most parents will now be familiar with the birthday party dilemma of needing to cater for egg-, nut-, gluten- and dairy-avoidant children, but if you ask grandparents, you will often hear the theory that food allergy and intolerance were uncommon in previous generations. It’s true, food intolerances and allergies with consequent dietary restrictions are becoming more and more common in western societies. Around 10% of children and 5% of adults in New Zealand have a food allergy. In some cases, food allergy is genetic and other members of the immediate family also have allergies.

An allergic reaction occurs when a person mounts an immune (infection fighting) response to an everyday external protein (allergen). The protein may be inhaled or eaten, or even just come in contact with the skin or eyes. The body’s immune system creates immunoglobulin E in response to the protein and a cascade of events follows, including release of histamine – the cause of many of the common symptoms associated with allergies.

Allergic responses tend to vary depending on the type of protein involved. Food proteins may cause symptoms such as a rash, facial swelling and breathing difficulties, and sometimes gut symptoms such as vomiting or diarrhoea. Airborne proteins tend to involve the nose or eyes causing, for example, hayfever or rhinitis.

Anaphylaxis is a more serious and potentially life-threatening form of allergic reaction. Anaphylaxis involves swelling of the tissues around the airway making it hard to breathe, as well as a drop in blood pressure and other more common symptoms of allergy. Anaphylaxis requires immediate treatment with an intra muscular adrenalin injection. People with severe allergy may carry an automatic adrenalin pen device, or an EpiPen, to use in case of accidental exposure to an allergen.

Why the increase?
There are many theories about why food allergies seem to have been increasing in recent generations. One theory is that the nature of our gut bacteria has changed significantly over the last few decades, affecting our immune system and potentially leading to an increase in food intolerances and allergies.

Gut bacteria are affected by antibiotic use and some studies have shown that children who received antibiotics in early life more frequently than others were then more likely to have a food allergy.

The method by which a baby is fed (formula versus breast milk) also affects gut bacteria, as does how a baby is born (Caesarean versus vaginal delivery). With both the rates of C-section deliveries and formula feeding having increased greatly over the last 50 years, there is a probable link here with the increase in allergies. 

The top offenders
Common allergens include:
Foods: Peanuts, egg, cow’s milk, shellfish and soy
Airborne: Dust mites, pollens and animals (cats or dogs)
Insect venom: Bees and wasps
Other substances: Latex and medicines 

Attempts to prevent
Other research has concentrated on how allergies can be prevented. In the early 2000s, pregnant women were told to avoid potential allergens and not to introduce them to their infants until their child was at least three years old.

Over the last two years, thinking around this topic has changed dramatically.

In 2015 a study on peanut allergy in children was published called LEAP (Learning Early About Peanut. Yes, really). This was a large study (650 infants) of babies aged 4-11 months who were at high risk of developing a peanut allergy. The babies were separated into two groups: one group received peanut snacks three times a week and the other group were told to avoid all foods containing peanuts. The children were followed up at five years of age and their rates of allergy were measured. The children who had eaten peanuts regularly had much lower rates of peanut allergy at age five than the group who had avoided peanuts entirely.

In the follow-up study (LEAPon), the same group of children were told to either avoid peanuts for a two-month period or continue eating peanuts. The group who avoided peanuts were more likely to go on to develop allergy to peanuts than the group who continued to be exposed to peanuts.

What does this tell us? Regular small exposures to peanuts may prevent peanut allergy in infants who are at risk of developing allergy. Continuing exposure is important to maintain tolerance to peanuts. And excluding peanuts (or possibly other food) completely for long periods of time in high-risk groups may cause or increase allergy to peanuts.

Other studies have shown smaller effects with other common allergens such as egg. 

Proceed with caution
Current guidelines in New Zealand and Australia recommend that babies start solids at about six months of age (but not before four months). Babies can eat family food containing egg, peanuts and other common allergens. It is best to introduce one new food at a time, just in case your baby has a reaction. There is some evidence that breastfeeding during the introduction of solids may decrease the chance of developing allergies.

A young baby’s facial skin is very sensitive and may develop a rash on contact with a new food, particularly if the baby is rubbing food around the cheek area (which is common!). This is a local skin reaction to something in the food and not a food allergy.

If your child has symptoms such as facial swelling or severe widespread rash immediately after eating a new food, you should see a doctor as soon as possible. Call an ambulance if there is any swelling of the lips or throat, or the child is coughing or struggling to breathe. Immediate treatment of an allergic reaction usually includes antihistamine. If the allergic reaction is severe it may require an injection of adrenalin and a period of observation. If the reaction is less severe and you are not sure if it was an allergic reaction, do not give the food again until you have seen your doctor.

It can be difficult to determine if a child is truly allergic to a food or other type of protein. As excluding foods can create problems, it’s best to see your doctor for advice before excluding a food from your child’s diet. Keeping a diary of food exposures and reactions may help your doctor to make a diagnosis. The doctor will also be interested in family history and any other medical problems your child has, especially eczema or asthma. 

Official results
Your doctor may arrange allergy testing to a particular food or protein. These can be either skin prick tests, blood tests, or in some instances, food challenges.

Skin prick tests involve exposing the skin to tiny amounts of potential allergens. The size of the reaction (redness or swelling) on the skin is then measured. Skinprick testing is usually done on the forearm but with babies it may be done on the leg. As many as 20 allergens can be tested this way. It’s important not to use any antihistamine for 10 days before the test, as this can interfere with the allergic response.

Allergy blood tests measure the levels of immunoglobulin E antibodies to a specific protein. This test is sometimes called a RAST test. Both the above tests can be positive in people who have not had allergic reactions so the result needs to be correlated with a good clinical history. Conversely, some people may have negative allergy tests but a definite reaction to food and there may be a different type of reaction involved.

The gold standard in allergy testing is a food challenge. This needs to be done in hospital and involves exposing a child to tiny amounts of a food in a controlled setting and watching for reactions. 

Food intolerance vs Allergy
Food intolerances are not caused by the allergic pathway but can be confused with allergy. Food intolerances usually have a slower onset than an allergic reaction and cause more gut symptoms such as bloating, abdominal pain or bowel symptoms. Commonly people with food intolerances may be able to tolerate a small amount of a substance (such as gluten) but find that large amounts will bring on symptoms. People with allergies will usually react immediately to even small amounts of a substance they are allergic to. 

On guard
Once a definite allergy is diagnosed, the mainstay of treatment is avoidance and symptom control if accidental exposure does occur. People with severe allergy may need to carry an action plan and an adrenalin device with them at all times.

De-sensitisation or allergy vaccination is currently undergoing research and can be considered in cases of moderate to severe allergy. Allergy vaccination involves regular injections of an allergen, in increasing concentrations over a period of months or even years. Desensitisation has been shown to decrease symptoms in some allergy sufferers when it is carried out correctly.

Most children will outgrow allergies to milk, egg and wheat, but allergy to peanuts and shellfish is more likely to persist into adulthood.

For further information, check out allergy.org.nz. 

Dr Abby Baskett (FRACP, IBCLC) is a paediatrician and lactation consultant working at Starship Children’s Hospital and Kidzhealth in Newmarket. She has a special interest in infant health, particularly feeding issues, and also performs tongue-tie assessment and divisions.