‘It triggers an explosion': What causes allergies and can they be prevented?

The Age

24-05-2025

Scattered across the bench were nuts chopped into jagged pieces. My mum was making a nut loaf. I was four and nagging my ailing grandmother to play with me. So Mum lifted me onto the bench and handed me a diversion: a Brazil nut to crack apart with my hands.
I turned the smooth kernel over in my hands then squeezed it hard until it began to crack. Suddenly, there was a strange pressure in my fingertips. 'Mum, can you help me cut my fingernails?' I said. 'Just a moment while I finish here,' she replied. My fingers were swelling now. I bit my nails and a small fragment of nut went into my mouth. My mouth started tingling. An itch spread in my throat. I felt lightheaded. I went to my bedroom where I started to cough and wheeze. Then welts showed up all over my skin.
The next thing I remember were my parents' concerned faces. If it were today, they would have taken me straight to an emergency department. As it was 30 years ago, they rushed me to a GP who gave me antihistamines and a puffer. The doctor monitored me for hours, fearing my breathing would worsen. Thankfully, it didn't. But tests in the days afterwards confirmed I had an anaphylactic response triggered by tree nuts (not to be confused with peanuts, which are, technically, legumes that grow underground). Allergists said it would have been much worse if I'd ingested any more than a sliver of Brazil nut – which, as it happens, is what I'm the most allergic to today.
As for other nuts, I admire them strictly from a distance: pastries with almonds; walnut-strewn Waldorf salads, Turkish delight rolled in pistachios. I carry an autoinjector of adrenaline, rarely eat cake at birthdays or weddings, pore over labels in supermarkets, and routinely flag my allergy with waiters in restaurants. (For an overseas trip, I learned to say it in French, 'Je suis allergique aux noix' and Spanish 'Soy alergico a los frutos secos'.)
The fear that a nut will evade my scrutiny can be wearying. Yet my experience is a blip among the millions of people with allergies in Australia. Around 5 million Australians live with allergies. A federal inquiry in 2020 found an estimated third of the population would experience them at some point in their lives. 'For many it is a tightrope to walk every day,' committee chair Trent Zimmerman wrote.
While the cause of allergies has been a major health conundrum this century, experts are homing in on answers. They appear to have slowed rates of peanut allergies among children, for example, after reversing guidelines on when parents should attempt to introduce common allergens to children. Meanwhile, talk of gluten, lactose and fructose intolerances is now commonplace. Is an intolerance the same as an allergy? How do you know whether you have either? What might cause allergies? And could we be nearer to a cure?
Have allergies become more common?
Every summer, London doctor John Bostock's eyes felt hot and itchy, his head felt full and he had sneezing fits. 'There is no absolute pain in any part of the chest, but a feeling of want of room to receive the air necessary for respiration, a huskiness of the voice and an incapacity of speaking aloud,' he wrote. It's a pattern familiar to anyone with hay fever, but this was 1819 and Bostock was penning the first modern description of an allergy (a term coined in 1906 by Austrian pediatrician Clemens von Pirquet). Today, hay fever, or allergic rhinitis, affects around one in five people in Australia and New Zealand. Back in 1819, Bostock could find only a few dozen fellow sufferers.
Australia had the highest rate of food allergies in children under five … But for food allergies among anyone under 18, Britain topped the list.
Experts today believe allergies are more prevalent than in recent decades, but they lack long-term studies that go back before the 1990s to show the exact rise. The Australasian Society of Clinical Immunology and Allergy (ASCIA) found in 2013 there had been a four-fold increase in anaphylaxis admissions to hospital in the 20 years prior.
Australia seems particularly prone to food allergies: they affect up to 10 per cent of children, according to a Murdoch Children's Research Institute Melbourne-based study from 2007 to 2011. Studies such as this have given rise to the catchphrase that Australia is the 'allergy capital of the world'. Two years later, a World Allergy Organisation review found Australia had the highest rate of food allergies for children under five, followed by Finland and Canada. But for food allergies among anyone under 18, Britain topped the list, with Australia ranking 11th.
What causes allergies?
Pinpointing what's behind allergies baffles researchers. Most believe the causes are 'multifactorial', a collision of lifestyle and biological forces. The 'hygiene hypothesis' posits that modern metropolitan life leads to fewer encounters with bugs, microbes, viruses and pathogens that would once have primed our immune systems. Indeed, researchers have observed that children in rural areas of Australia, Canada and Europe show lower rates of asthma and allergies such as hay fever than those in cities. Other studies have found having older siblings or a pet dog lessens children's chances of developing egg allergy. 'I think there's an important concept here,' says Gideon Lack, a world-leading allergy researcher in London. 'But there are so many factors that change with civilisation and social habits that it becomes almost impossible to pick one unique change.'
A related area of research zeroes in on the microbiome in our gut and skin (and in orifices such as the nasal passage and mouth). It is a layer of trillions of viruses and bacteria that supports the immune system and helps us digest food. 'If you don't interact with nature and you don't have a healthy diet, you will lose species in your microbiome, and that puts you at risk of developing all sorts of diseases, including allergies,' explains Professor Michaela Lucas, a WA-based immunologist at the National Allergy Centre of Excellence.
However, research into the microbiome is still at an early stage. Says Lack: 'The problem with this hypothesis is that it's a hard one to test because our methods of quantifying the microbiome I would consider to still be primitive.' What about lack of early exposure to certain foods? Lack has shown that babies being introduced to allergens from around four months old does help prevent allergies (more on this in a moment). Still, he doesn't think allergies have any single cause. 'It may be that we need a number of necessary conditions that are, in themselves, insufficient to promote tolerance; we need early exposure to the foods, and we need the right sort of bugs on our gut, on our skin. I think all of that makes a lot of sense.'
Another factor could be having low rates of vitamin D, which plays a role in regulating the immune system. Babies who are vitamin D deficient are much more likely to have egg or peanut allergy by the age of one, says Professor Kirsten Perrett, director of the National Allergy Centre of Excellence. It's not clear yet whether this is a cause or an association (perhaps children exposed to less sunlight are also exposed to fewer allergens outside). Still, it could help explain allergies in cities such as Melbourne. 'Potentially, it's that perfect storm because we live in a very hygienic environment, and – similar to other cities further away from the equator – we also have low UV, high rates of vitamin D deficiency, and additionally, we don't fortify the food chain with vitamin D,' says Perrett.
Several genes have been linked to an increased risk of food allergies, says Perrett. But what seems to have more of an influence is the interplay between genes and the environment. For example, MCRI research has found an increased risk of peanut allergy in Melbourne infants where one or both of their parents were born in East Asia. This is despite rates of allergies being lower among Asian parents.
Weather patterns can factor in, too, with some allergies. Heavy spring rains boost pollen-producing grasses on many of our city fringes, in temperate regions across the south of Australia, aggravating the hay fever-prone. The pollen can combine with a particular type of storm front to create thunderstorm asthma events that affect those who previously did not know they were susceptible to asthma. In 2016, Melbourne had the most severe thunderstorm asthma event on record, when extreme grass-pollen levels led to 3365 people going to emergency departments and 10 deaths.
Yet it is possible to trace some allergies to a specific cause. In the 1980s, Professor Sheryl van Nunen, an allergist on Sydney's Northern Beaches, started to notice an increase in people who had an anaphylactic reaction to meat. Over the next decades, she pieced together that the patients – none of whom had reacted to meat in the past – had been recently bitten by a tick common to Australia's east coast. An increase in cases had come as fox bating became widespread and small animals proliferated. Nunen has found the tick picks up a sugar molecule called alpha-gal from animals and introduces it to humans through biting their skin. When the person next eats meat, Nunen tells us, 'there are rapidly evolving allergic reactions that occur'. A feat of sleuthing? 'Parasites and allergy are so closely entwined in the immunologist's mind that I don't find this to be a super bright thing to do,' she tells us. 'I just think you trip over it when you hear people tell they've had a tick bite. I always teach my medical students to not just ask, why? Ask, why not? You'll get there faster.'
How do you know if you have an allergy?
People can have allergy-like symptoms that are not allergies: think of someone experiencing bloating and cramps from a lactose intolerance (which can affect up to 90 per cent of people from some areas of East Asia and up to 65 per cent from Africa) or someone with sensitive skin getting a contact rash from soap. While an allergy involves a foreign protein affecting the immune system, in almost all intolerances, the protein is isolated to the digestive system or the surface of the skin. An intolerance can cause anything from mild discomfort to chronic pain but intolerances do not cause anaphylaxis – same with the autoimmune condition Celiac disease, which is different again, and which affects one in 70 Australians.
Common food allergens are eggs, cow's milk, peanuts, tree nuts, sesame, soy, wheat and seafood, although almost any food can prompt an allergic reaction. Again, scientists aren't sure why, but they do know that some of the proteins in these foods (and in substances such as cat dander, or skin) are slow to break down, giving the immune system more time to recognise them and react. Others possibly cross from the gut into the bloodstream where the immune system detects them.
Once an immune system has learned to recognise a protein as harmful, the results, on a cellular level, can be extreme. Antibodies called IgEs become attached to a person's immune cells, both in their blood and tissue, such that those cells will detonate if the body comes into contact with the protein. An IgE is analogous to a land mine, says Kirsten Perrett. 'It basically triggers an explosion releasing chemicals such as histamine that cause the symptoms such as swelling, hives, difficulty breathing, a drop in blood pressure, and making you very sick.'
In the most serious cases, people experience anaphylaxis: their breathing becomes obstructed, or they experience a drop in blood pressure that can send the cardiovascular system into shock. Victoria Currier, a childcare worker from Ipswich, gave her son, Zion, a bottle of milk formula when he was three months old. 'He broke out in a red hive rash all over his body, his ears swelled, couldn't breathe, was vomiting, the full anaphylactic episode,' she tells us. 'Within 15 minutes, we were in the back of an ambulance.' Tests have shown Zion, now two, is allergic to dairy products, eggs and shellfish.
'Some people only develop reactions after they've been stressed or they've been doing exercise.'
Most people have less acute reactions. It's rare for hay fever, for example, to cause anaphylaxis. Food allergies commonly cause hives and vomiting, and reactions to insect stings often cause swelling. The severity can depend on how much allergen the person is exposed to, says Perrett, and your health at the time. 'If you are unwell with an infection, for females if they're menstruating, if you're taking certain types of medication such as non-steroidal anti-inflammatory drugs [NSAIDs], if you're very tired – your immune system threshold will be lower. Some people only develop reactions after they've been stressed or they've been doing exercise.'
Blood tests and skin prick tests – where a doctor applies drops of allergens on the arm or back then pricks the skin and records the size of any resulting lumps – can show if someone has an allergy but, crucially, can't determine its severity. 'The test is positive or the test is negative,' says Dr Joanne Smart, the Royal Children's Hospital's director of allergy and immunology. 'We have no test to predict severity of allergy, or risk for anaphylaxis.'
The only other method is to undertake a 'challenge', where doctors gradually expose the person to increasing amounts of an allergen in a hospital over several hours. Doctors at the Royal Children's Hospital in Melbourne might suggest a child undergo a challenge depending on the size of a skin prick test, how long ago their last reaction was, how severe that reaction was, and what types of symptoms they had. The test will assess whether children have outgrown some food allergies, common for milk and egg but less so for nuts, sesame or seafood. (I 'failed' two challenges as a teenager, vomiting once and my lips swelling the other time.)
Some 90 per cent of people who believe they are allergic to penicillin are wrong.
Allergies can have a high rate of overdiagnosis and mislabelling. Some 90 per cent of people who believe they are allergic to penicillin are wrong, says Michaela Lucas. 'Often this comes from what happened to you as a child – your mum told you to avoid it, maybe because you had a rash when you were on a penicillin while having a virus or bacterial infection,' she says. 'Penicillin allergy is a tricky one because we don't have any reliable laboratory test or blood test which can tell who's allergic and not. Skin testing can also be unreliable so we have to challenge people.'
Meanwhile, during recent peanut challenges to select infants for a treatment program, many were found not to have the allergy at all, says Joanne Smart. In people who've never had an allergic reaction, screening by skin prick or blood test has high rates of false positives (a lump might form on their skin but they won't have symptoms when actually exposed to the allergen). 'Parents commonly request allergy testing of their child just in case,' Smart says. 'They often come in and they say, 'I'm allergic to peanuts and tree nuts. Can we test my child just to check?''
How do you prevent allergies then?
In the early 2000s, the health advice for preventing food allergies among young children was to avoid eggs until after 12 months and typical allergens such as nuts until a child is three or older. Around this time, Gideon Lack, who is a professor of paediatric allergy at King's College, gave a lecture in Tel Aviv when he asked the audience how many people they had seen with a peanut allergy in the past year. Only a few raised their hands. 'Had I given that talk in Australia at the time, and certainly in England, virtually every pediatrician and allergist would have put up their hand,' Lack tells us from London. 'We questioned, why this is?'
It led Lack to confirm children in Britain were 10 times more likely to have a peanut allergy than in Israel. At the same time, Lack discovered that many parents in Israel were giving babies a snack called Bamba, a corn puff dusted in peanut butter. Lack went on to conduct another study called Learning About Peanut Allergy (LEAP) that enrolled babies and either gave them regular servings of peanuts or instructed them to avoid the legumes for the first five years of life. The results were staggering: the group that ate the peanuts showed a 90 per cent reduction in peanut allergy.
'If you introduce these foods in good quantities, several times through the course of the week … The body learns this is a friend and becomes tolerant.'
Lack's findings overturned food allergy advice worldwide. 'It was incredibly exciting,' he says. 'We weren't expecting such a dramatic effect.' In Australia, guidelines changed in 2016 to recommend that babies be introduced to common allergy-causing foods by 12 months of age, and not before four months. The foods include egg, peanut, cow's milk, tree nuts, soy, sesame, wheat and seafood. Guidelines from the peak body of allergy specialists, ASCIA, include that only one food should be tried at a time so any reaction can be linked to it; and foods such as nut butters and cooked eggs should be introduced in tiny amounts. (It can be rubbed on the inside of the baby's lip as a starting point, the guidelines say; if there is no reaction, the food can be mixed with the baby's usual meal and gradually increased over several days. For example, the Royal Children's Hospital Melbourne advises ⅛ teaspoon on the first day, ¼ teaspoon on the next, and so on.) If the baby has a reaction at any point, the parents should seek medical help. (Note: this is a brief account of more detailed public guidelines, and not medical advice specific to your child.)
Kirsten Perrett says it's important any allergen, such as peanut butter, isn't smeared on the baby's skin outside the mouth because this can cause a skin reaction that could be confused for an allergy. If a small amount of redness occurs, she recommends stopping, washing the baby's face, and trying the same or a smaller amount of food again later. 'Most of the time, we know that a little bit of redness is not equal to allergy.'
All the same, parents of children with dry skin or eczema should pay particular attention. There is increasing evidence that children become allergic to allergens because they absorb them through the skin before they digest them, causing the immune system to see the allergen as a threat, says Lack. Indeed, he has found children with eczema are four times more likely to have a food allergy. 'If you tell a baby's parents with eczema not to feed that baby peanuts, egg, milk – which is what we did for a long time – the baby will only be exposed through the skin and develop an allergy,' Lack says. Again, orally introducing food allergens to babies from four months of age could help prevent this. 'If you introduce these foods in good quantities, several times through the course of the week, the gastrointestinal exposure overrides the skin exposure. The body learns this is a friend and becomes tolerant.'
While Australian families have been following the advice to introduce allergens early since 2016, there hasn't been a significant drop in the rate of food allergy as a result, says Perrett, 'but what we haven't seen is a continued rise.' The Murdoch Children's Research Institute found rates of peanut allergies had not increased in 2018-19 compared with 2007-11, suggesting the new guidelines could have blunted an increase. But what about any adverse effects on babies? Perrett has found a slight rise in babies attending hospitals but no increase in anaphylaxis, actually being admitted to hospital, or requiring adrenaline. 'These results provide reassurance for parents and clinicians of the safety of this food allergy prevention practice.'
Could there be a cure for allergies?
Austin Tattersall's allergies have been front of mind for him ever since he could first help himself to food. His parents had learned he was allergic to eggs, dairy products and nuts when they'd first given them to him as a baby. Over the years, he's had rashes and episodes of vomiting. The allergy has kept the now 25-year-old from travelling overseas. 'Through my university I was contemplating on whether I was able to make it to Spain for a couple of weeks,' Tattersall says. 'I didn't end up going because I didn't feel safe. I've mainly just travelled interstate … and it makes it so much easier to know that there's a Coles around the corner that stocks the same stuff that I've got at home.'
'… if someone accidentally drinks from his drink bottle, or he drinks from somebody else's drink bottle … that in itself is a risk.'
Over the years, food labelling has become clearer and restaurants more accommodating. (Cafes, restaurants and food producers are now legally required to declare common allergenic ingredients.) 'Compared to when I was little – when the restaurant would just sort of laugh at you and go, 'Oh that can't be real, you don't have allergies at all' – the perception and stereotype has changed a lot,' he says. 'Education, as well, has been one of those big things in terms of changing people's mind, changing people's perspectives, that has made it so much easier for my adult life.'
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The most nerve-wracking time for parents is when a child with an allergy is young. 'I've become a lot more anxious as a parent, just because I know how severe it could be,' says Victoria Currier of Zion's allergies. 'Before, I would go to the park and things like that without any worry. Whereas now, I'm like, is this something we should be doing? Is it going to be safe? Do we really have to do it?' She worries more as the two-year-old becomes increasingly mobile. 'In older rooms at childcare, there's things like drink bottles; if someone accidentally drinks from his drink bottle, or he drinks from somebody else's drink bottle … that in itself is a risk.' (Action plans for children at risk of anaphylaxis are commonplace nowadays in school and childcare staff rooms.)
Specialists hope for a day when many allergies are curable. 'Historically, there have been no treatments for food allergy in Australia,' says Perrett. She knows of some patients with severe allergies who have travelled to the US to receive oral immunotherapy – a process that introduces them to precise dosages of an allergen under controlled conditions. The dosage increases over months or years to raise their threshold of tolerance (this is unlike a food challenge, which is done over several hours to test whether a reaction will occur). Studies with peanut, egg and milk have shown this can desensitise between 60 per cent and 80 per cent of patients. In Australia, an oral immunotherapy program in 10 hospitals is under way for babies with peanut allergies. 'The National Allergy Centre of Excellence is evaluating the program and we hope that if it's successful, we'll be able to roll it out for more allergens and importantly, expand the program to more hospitals and those in regional centres too,' says Perrett.
'At the very least, allergies make life more complicated. At their worst, they come with a lifetime of worry.'
Other treatments being clinically trialled around the world include introducing allergens via skin patches (epicutaneous immunotherapy), vaccines and peptide immunotherapies, and injections such as anti-IgE antibodies that dampen the immune response. Since the early 2000s, Australia has had an immunotherapy program to prevent anaphylaxis from Jack jumper ant bites in Tasmania, Victoria and South Australia, where the ants are the second most common cause of insect-sting anaphylaxis (after bees).
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Meanwhile, there's never been a repeat of the dreaded Brazil nut incident for me. In part, that's been made possible by people asking about dietary requirements before social events; and I'm used to self-monitoring now, although I sometimes go to restaurants without an EpiPen and worry about why I did, while other times I'm overly cautious and default to ordering a plain croissant at a cafe. At the very least, allergies make life more complicated. At their worst, they come with a lifetime of worry. 'People are wanting to do everything they can,' Perrett tells me. 'It really does impact everyone, not just that person but the family, the community. At a birthday party, they worry about the child that has allergies and how they can prevent them having a reaction on their watch.'