The habits that help prevent allergies

As a child, Isabelle Gerretsen suffered from a wide range of food allergies. Could scientific advances save others from having to endure the same fear and stress?

When I was four years old, I drank my first glass of milk in a hospital, with an IV drip in my hand to administer emergency medication in case I had a severe allergic reaction.

The doctors were carrying out a food challenge to see if I could tolerate cow's milk, which I'd been allergic to since I was tiny. I was first given a drop of milk on my tongue, followed by a few sips, and eventually a full glass. These challenges happened regularly and often resulted in vomiting and a rash, but luckily nothing more serious.

I outgrew my dairy allergy at the age of 7. But to this day, I can't drink a glass of dairy milk as it makes me feel nauseous, presumably because my mind still associates the taste with feeling sick.

I was a highly allergic child, suffering from dairy, egg and nut allergies. Looking back, all the warning signs that I would develop food allergies were there. Not only did I have a history of allergies in my family, I also suffered from severe eczema as a baby, which doctors now say is a red flag.

I was lucky, I never suffered from anaphylaxis, when allergens cause the immune system to go into a state of shock and trigger severe and potentially life-threatening symptoms which can include breathing problems, vomiting and a weak pulse. Instead I would suffer from hives, stomach cramps and an itchy throat if I ate any dairy or eggs. I have only accidentally once had a tiny amount of peanut, which caused severe vomiting and stomach cramps, but luckily no hospitalisation.

My food allergies meant my diet was severely restricted during childhood. There weren't a wide range of dairy-free alternatives available during the 1990s, so I spent the first eight years of my life missing out on cake, chocolate and cheese. This may seem like a small sacrifice – after all, many people voluntarily skip such treats, be it to cut their sugar intake or avoid animal products. But food allergies are different. They mean constantly having to be alert to potential threats in every meal. Those living with them probably won't be surprised to hear that food allergies are known to impact the quality of life and mental health of children and adolescents, as well as their families. And while in the UK, deaths from allergic reactions to food have declined over the past 20 years, there are still cases of fatal anaphylaxis.

I was lucky to outgrow two of my three allergies (dairy and eggs) and today they don't impact my daily life. But allergies are becoming a daily worry for more and more children and parents, often causing severe anxiety and stress.

The medical advice has changed hugely since I suffered from food allergies as a child. Rather than practicing strict avoidance, doctors are encouraging parents of children at risk of allergies to introduce them to peanuts, eggs, milk and other potential allergens as soon as they start having solid foods. Could these scientific advances help us save future generations from the stress and danger of food allergies – and perhaps even make existing cases less severe?

Tide of allergies

Child allergies are rising at an alarming rate, particularly in industrialised countries. "We see that the incidence and prevalence of food allergies is increasing throughout the world," says Kari Nadeau, professor of paediatric medicine and director of the Sean N Parker Center for Allergy & Asthma Research at Stanford University. She calls the rise an "epidemic" in her book, The End of Food Allergy.

Allergy is the most common chronic disorder in children in the UK, affecting 40% of children – among the highest rates in the world. However, as researchers have pointed out, a lack of accurate data around allergy prevalence and increased use of the term "allergy" can make it difficult to directly compare rates in different countries.

In the US, studies suggest that between 3.9% and 8% of children and adolescents are affected by food allergy. In Australia, researchers conducted a study of the 2,848 one-year-olds, based on results from food challenges – a method that is thought to yield particularly precise data. They found that more than 10% of them had a challenge-proven food allergy to one of the common allergenic foods, such as raw egg and peanuts.

The idea that allergies are increasing is backed by many different sources, from surveys to hospital admissions. Between 1997 and 2011, the prevalence of food allergies in children in the US increased by 50%. Between 2013 and 2019, England saw a 72% rise in the number of hospital admissions for children caused by anaphylaxis.

"The other big change in epidemiology is that more and more people have multiple food allergies," says Nadeau. "They're not just allergic to milk or egg or peanut, they now also have wheat, sesame or tree nut allergies."

How do children become allergic?

"Children aren't born allergic," says George Du Toit, professor of paediatric allergy at King's College London. However, genetics can make it more likely for a baby to develop an allergy at some point. If both parents have allergies, children have a 60-80% risk of also developing one, compared to a 5-15% risk among children without allergic parents.

But while some babies may have a higher risk of developing allergies later, due to these inherited traits, they don't develop them while still in the womb."There's nothing in pregnancy that we've seen that can induce food allergy," says Nadeau. It is important that mothers realise this, she says. Many have asked her "What did I do wrong?" when their child develops an allergy, thinking it may be linked to their diet during pregnancy. But there is no evidence for this, Nadeau says.

It is during the first weeks and months of their lives that babies are exposed to allergens in their environment and start developing antibodies. This exposure is through the skin, not the gut, says Nadeau.

"The moment a 'foreign object' touches our skin, even on a microscopic level, those allergic pathways start to be embedded in the system, and we start to activate B cells and T cells, that set down memory responses for life," she explains. B cells and T cells are two cell types that play a very important part in our immune response. They allow us to react to a perceived threat, and remember that reaction so it's faster and stronger the next time the threat appears.

This means that a child can be exposed to peanuts through dust or residue on their parents' hands, which can trigger an immune response long before they have ever eaten peanut protein.

By the time they eat the food for the first time, they may already be allergic.

"If the body is first and repeatedly introduced to foods through the skin, as opposed to through the mouth and gastrointestinal tract, it may increase the likelihood of sensitisation to that food, and possible allergy," says Jennifer Bufford, vice president of clinical operations at Food Allergy Research and Education (FARE) in the US.

Children with eczema, which causes skin to become dry, broken and itchy, are particularly vulnerable to developing a food allergy. This is because their skin has microscopic holes in it, which allow particles to enter the body, says Nadeau.

"Early onset, severe eczema, particularly if it's distributed in exposed areas, such as the face, neck, arms and legs, is a red flag and a real root of exposure," says Du Toit.

It begins with the skin

Infants with eczema are six times more likely to have an egg allergy and 11 times more likely to have a peanut allergy by 12 months than infants without eczema, according to a population-based study of one-year-old children in Melbourne, Australia.

In the UK, one in five children under the age of two has eczema. The number of children with eczema and allergic rhinitis in the UK has more than trebled since the 1960s.

The exact cause for the rise is not known, but Nadeau believes an increase in the use of detergents and harsh soaps as well as rising pollution levels may play a role. Laundry detergents that contain the enzyme protease may impair the skin barrier and increase allergen sensitisation, she says. "Detergents are very concentrated and really clean our clothes but also, unfortunately, degrade our skin."

"Our modern, industrialised environment has likely increased our susceptibility [to eczema and allergies]," says Bufford, adding that smoking, traffic fumes and air pollution are all thought to play a role in contributing to allergies.

Environmental disasters such as wildfires may worsen the problem. Short-term exposure to wildfire smoke has been linked to increased eczema and general itchiness, including among people with no history of the skin condition, according to research carried out by scientists at UC San Francisco. A study by Nadeau and researchers at Stanford University found that exposure to wildfire smoke was linked to significantly lower concentrations of type 1 T helper cells (Th1) in children, which fight infection, and higher levels of type 2 T helper cells (Th2), which trigger the activation of cells involved in allergic inflammation.

"The body's immune system is in a state of constant flux, with various cell types increasing or decreasing depending on what the body is being exposed to," Mary Prunicki, the study's lead author, said at the time of publication in 2019. "In this study, we found that there were more [Th2] cells in children who were exposed to the wildfire smoke, which was more pollution exposure overall." More Th2 type cells are known to induce more acute and chronic allergies and asthma, Nadeau explains. This is because they activate allergen-specific B-cells.

Research from the Canadian Healthy Infant Longitudinal Development (CHILD) study in 2015 found that exposure to traffic-related air pollution in the first year of life increases the risk of developing allergies to food, mould, pests and pets.

Peanut protein found in house dust has also been linked to the onset of food allergies. One study by researchers at King's College London found a strong link between early-life exposure to peanut protein in household dust and peanut allergy in children with the FLG mutation, which is associated with eczema. A three-fold increase in peanut dust exposure during infancy was associated with a three-fold rise in school-age peanut allergy.

"Children with that mutation are much more likely to have dry skin and we found that if they had high peanut dust levels in their bed or play area, they had a significantly increased risk of developing a school-age allergy," says Helen Brough, lead author of the study and a consultant in paediatric allergy at the Evelina London Children’s Hospital in London.

"My top tip would be that all parents who apply creams onto their child's skin should wash their hands before doing so because there might not just be bacteria on their hands, but also peanut, egg or sesame," says Brough.

"When they buy those types of ointments, parents should never put their hands inside [the contrainer] because then that will be contaminated with bacteria and potentially food," Brough says. Instead they should use a clean spatula to put the cream onto their child's skin before rubbing it in by hand, she says.

Preventing peanut allergies

A landmark study in the UK triggered a paradigm shift in how child food allergies are treated and showed that peanut allergies are preventable, if parents intervene early.

In 2015, the Learning Early About Peanut Allergy (LEAP) study revealed that the number of children developing a peanut allergy can be drastically reduced if they are regularly fed peanuts from a young age. (Parents interested in using this method should always discuss it with their own healthcare provider first, and ensure it is appropriate and safe for their baby. The findings reported here are only intended for information, and not as medical advice).

The study enrolled 640 infants aged 4-11 months who were considered at high risk of developing a peanut allergy because they had severe eczema, were allergic to eggs or suffered from both conditions, until the age of five. The children were divided into two groups: those whose parents regularly fed them food containing peanuts, in at least three meals a week, and those whose families avoided peanuts altogether.

The LEAP study found that regular peanut consumption reduced the prevalence of peanut allergy at five years of age by a remarkable 81%.

By the time they were five, just 3.2% of the consumption group had developed a peanut allergy, compared to 17.2% in the avoidance group.

"The difference between the two groups was enormous," says Du Toit, who is one of the LEAP study's co-authors. These scientific findings have "revolutionised" how children's allergies are treated, he says.

"The advice used to be 'if you don't go near this allergenic villain, you won't develop a problem'", says Du Toit. "But all you do is kick the can down the road, and just give the child a longer opportunity to become allergic."

Nadeau has turned this scientific understanding into a memorable rhyme:

"Through the skin, allergies begin;

Through the diet, allergies can stay quiet."

New advice

After the LEAP study was published, the American Academy of Pediatrics endorsed early peanut introduction in infants at high risk for peanut allergy. In 2017, the National Institute of Allergy and Infectious Diseases in the US published new guidelines for introducing peanut foods to infants aged four to six months with severe eczema or egg allergy and from six months for children with mild to moderate eczema.

Previously the guidelines recommended that parents should delay the introduction of certain high-risk foods (such as peanuts), which "may have played a part in the ongoing rise of children with allergies to food," says Bufford.

The British Society for Allergy and Clinical Immunology also published new guidelines for the treatment of nut allergies in 2017, recommending the early introduction of peanuts into the weaning diets of high-risk infants.

Many parents are "very nervous" about introducing their babies to peanuts and other foods they may be allergic to, particularly if there is a family history of allergies, says Maeve Kelleher, honorary senior clinical fellow at Imperial College London, and consultant in paediatric allergy at Children's Health Ireland. 

If this is the case, it may be worth doing a skin test first or suggesting that the introduction takes place in a hospital setting, says Kelleher. In babies under the age of one, anaphylaxis is "very unlikely", she says, adding that the most common allergic symptoms among infants are hives and sometimes vomiting.

"Once the child is older, and their immune system is more sophisticated, they're more likely to have anaphylaxis," says Brough.

Du Toit says it is important for parents to be aware that there is a "window of opportunity" to establish tolerance, between 4-11 months.

Parents should start weaning their children on to as many different foods as possible, especially if they have eczema, he says. 

"It's rare to be allergic to just one food; where you find one food allergy, you usually will find others," says Du Toit. "When you find one, the clock really is ticking and the window of opportunity starts closing. Ideally, you want to be weaning onto other common safe food allergens." By the time the baby reaches 12 months, it's often too late as the allergies are already established, he says.

"A lot of allergies go together because they share common proteins, especially shellfish," says Nadeau. "So if you're allergic to shrimp, you're more likely to be allergic to other items that have an exoskeleton like lobster."

Therefore it is important to introduce infants to a wide range of food in the first year of their life, she says.

Is being 'too clean' really a problem?

One of the most discussed topics when it comes to allergies is whether cleanliness is to blame for rising allergies.

The hygiene hypothesis, which was postulated by epidemiologist David Strachan in 1989, proposes that early childhood exposure to germs and infections helps the immune system develop and protects against allergies. Strachan argued that the rise in allergies and asthma in the late 20th Century was linked to children's reduced exposure to microbes through declining family sizes, limited interaction with animals and higher standards of cleanliness.

The theory is contentious and many scientists disagree with it, arguing that good hygiene is vital to protect against disease and that there is no good evidence showing that cleanliness is responsible for the development of allergic diseases.

A widely supported interpretation of the hypothesis is that a child's susceptibility to allergies doesn't have to do with how clean their home is, but rather with whether their gut has been exposed to different types of microorganisms.

In a 2021 study, researchers at University College London and the London School of Hygiene & Tropical Medicine argue that we are not too clean for our own good, pointing out that children's exposure to vaccines, their natural environment and their mothers' beneficial microbiota provides all the microbial inputs needed for a healthy immune system.

The study shows that cleaning the home "does not necessarily reduce the child's exposure to mother or to nature, while the unnatural microbiota of the modern home are not helpful, and can be toxic," says Graham Rook, emeritus professor of medical microbiology at UCL and lead author of the study.

While cleanliness in the home is no longer considered a risk factor for allergies, environmental factors can play a role in the development of their immune system and allergic conditions.

"Children that are born in a farming environment are much less likely to have asthma, eczema and allergies," says Brough. "That's thought to be due partly to the food that they're eating and partly to their exposure to bacteria that are in stables."

A study carried out in South Africa concluded that exposure to farm animals protected toddlers aged 12-36 months from allergic outcomes.

Research on Amish children raised on farms in Indiana provides an even more detailed picture. The Amish are a farming community of Swiss descent, who typically live in large families and follow a traditional lifestyle, such as avoiding the use of electricity, and using horse-drawn buggies instead of cars. The researchers compared the Amish children to Swiss children raised on farms, and also to Swiss children who did not live on farms.

All of these children shared a similar genetic background, but their allergy and asthma rates were very different. The Amish children had the lowest rates of asthma and allergies, while the Swiss children not raised on farms had the highest, comparable to general rates in the US. The Swiss farm children's rates were in the middle.

The results suggest that lifestyle rather then genetics play a decisive role in the development of asthma and allergies, and especially that being in close contact with animals helps. The reason for the difference between the Amish and Swiss farm children was not entirely clear, and may be to do with the size of the families, according to the study.

"In this rural environment exposure to livestock is the strongest protective factor," the researchers said. "In urban communities, where animal contact is rare, risk factors include caesarian section, and protective factors include consumption of fermented milk products."

Birth and gut health

Research suggests that there is a link between how a baby is born, their gut bacteria, and later food sensitivities. Babies delivered by vaginal birth, and exposed to their mother's vaginal and intestinal bacteria in the process, have been found to have higher gut bacterial counts than those delivered by caesarean section. A study by Canadian researchers established a link between children born via caesarean section and peanut sensitivity in infants. These children had persistently low levels of bacteroides – a type of bacteria critical to the development of the immune system – in the first year of their life, the study noted. The babies with low bacteroides were found to have a threefold increase in their risk of developing peanut sensitivity by the age of three.

"It all boils down to the gut microbiome," says Brough. "We know that children with food allergies have a different gut microbiome to children without them."

Many mothers who have caesarean section are given antibiotics after the birth, to prevent infection of the wound. While this is important for the mother's health and recovery,  Brough says it can have a negative side effect: "We know that exposure to antibiotics in the first couple of weeks of life increases the [baby's] risk of eczema."

This does not mean babies born via caesarean section will definitely develop allergies – and as the LEAP study shows, they can benefit from preventative strategies. But it may shed a useful light on the root causes of allergies.

Growing out of allergies

I luckily outgrew my milk and egg allergies, but am still unable to eat nuts of any kind. This appears to be common. Roughly 80% of children will grow out of their milk and egg allergies, says Kelleher. "But unfortunately only around 20% grow out of a nut allergy."

"Although allergies to milk, egg, wheat and soy often resolve in childhood, children appear to be outgrowing some of these allergies more slowly than in previous decades, with many children still allergic beyond the age of five," says Bufford. Allergies to peanuts, tree nuts, fish and shellfish are generally lifelong, she says.

But even for these allergies, there are treatment options emerging. Immunotherapy, which desensitises the body to an allergen, is a particularly promising treatment. Immunotherapy drugs have been found to induce remission of peanut allergy. In a recent clinical trial in the US, giving peanut oral immunotherapy to highly allergic children aged one to three years – under close medical supervision – desensitised most of them to peanuts and induced remission of peanut allergy in one-fifth. This kind of immunotherapy is different from the preventative steps for babies, and is carried out by experts at specialised medical centers, not by the parents themselves.

Although food allergies are rising rapidly around the world, we are finally starting to understand how to effectively treat them, and prevent them altogether through early intervention.

I know just how life-changing these scientific developments can be. It means that future generations of young children can enjoy carefree play dates and birthday parties, without the risk of becoming incredibly unwell, and that their parents are not plagued by constant fears about hidden allergens.

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