The microbiomes in our gut and mouth may determine whether people with a peanut allergy develop a life-threatening reaction. This could help explain why some people with the allergy experience relatively mild reactions, while others develop severe, or even fatal, symptoms.

“There’s a big question around why some patients are more susceptible to more severe reactions,” says at the Autonomous University of Madrid in Spain.

Peanut allergy occurs when the immune system mistakenly identifies proteins in the legume as a threat, causing it to produce excessive amounts of a particular type of antibody. This ramps up inflammation, leading to symptoms such as itching, swelling and vomiting. In extreme cases, peanut exposure causes anaphylaxis, a life-threatening reaction that typically involves breathing difficulties.

Jiménez-Saiz and his colleagues wondered whether the microbes that live on and within us play a role here, given the huge influence that our body’s various microbiomes have on our immune system.

To find out, they inserted a small amount of peanut into the stomachs of three groups of mice without any allergies. The first group was reared to develop no microbiome (known as germ-free mice), while the second had a minimally diverse microbiome, and the third had a microbiome that is typical of a healthy mouse.

Forty minutes later, the team found higher levels of two proteins that play a major role in peanut allergy, known as Ara h 1 and Ara h 2, in the small intestines of the germ-free and minimal-microbiome mice than in those with the most diverse microbiome.

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Further analyses revealed that the latter group carried the highest levels of a group of bacteria called Rothia, especially the strain Rothia R3, which is involved in digesting and degrading peanuts in the gut.

To explore whether Rothia R3 influences anaphylaxis risk, the researchers induced severe peanut allergies in a separate group of mice, which had a minimally diverse microbiome.

They then implanted Rothia R3 into some of their guts, before delivering peanut paste directly into all of the animals’ stomachs. Forty minutes later, all the mice had developed anaphylaxis, but the body temperature of those that received Rothia R3 had dropped by just 2 per cent, on average, compared with 3.5 per cent for the mice that didn’t receive it. Anaphylaxis typically causes a drop in body temperature, which can lead to hypothermia and organ failure.

The Rothia-implanted mice also had about half the levels of an immune molecule called MMCP-1 in their blood, which usually rises during anaphylaxis, compared to the control mice. “The findings are compelling,” says at Imperial College London. “If a similar immunological change occurred in people, you would expect this to reduce the severity of anaphylaxis symptoms.”

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In another experiment involving 19 people with peanut allergies, the team found that those with a greater tolerance of peanuts had substantially higher levels of Rothia bacteria in their saliva than those with more severe allergies. This suggests that the presence of these bacteria in people’s mouths, as well as in their gut, influences their anaphylaxis risk.

Rothia probiotics could one day reduce the severity of anaphylaxis developing during a peanut allergy reaction, says Shamji. “The need for something like this is huge,” he says. It could particularly alleviate fear around accidental exposure to peanuts and reduce the risk of adverse reactions during oral immunotherapy, which aims to treat allergies by gradually exposing people to increasing doses of an allergen, he says.

The team hopes to demonstrate the potential of such a treatment in a clinical trial by giving people with peanut allergies either Rothia probiotics or a placebo, before exposing them to low levels of peanuts, says Jiménez-Saiz.

Around one in seven cases of life-threatening allergic reactions seem to be caused by foods not typically labelled as potential allergens on a product’s packaging, prompting researchers to argue policies around this need to change.

Food allergies are becoming more common, but many official allergen lists have not been updated in years. For instance, the European Union’s states the presence of 14 food allergens, like peanuts and soya, must be made clear on products, but is based on data from 2011.

To understand the lesser-known triggers, at Centre Hospitalier Universitaire de Reims in France and her colleagues analysed 2999 cases of food-induced anaphylaxis – a life-threatening reaction – voluntarily reported by doctors to the Allergy-Vigilance Network, which collects data from French-speaking countries, between 2002 and 2023.

They were specifically looking for emerging food allergens, which they defined as any foods that were not on the European mandatory labelling list, but which were individually responsible for at least 1 per cent of cases.

The team found goat or sheep milk and buckwheat triggered 2.8 and 2.4 per cent of cases, respectively. These were followed by peas and lentils, alpha-gal – a sugar that can trigger an allergy to red meat and other mammalian products – pine nuts and kiwi, which each set off between 1 and 2 per cent of incidences. Apples and beehive products like edible pollen, honey and royal jelly caused 1 per cent of cases.

Overall, emerging food allergies were responsible for 413 – roughly 14 per cent – of the reported cases.

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In terms of reaction severity, goat and sheep cheese provoked particularly dangerous reactions, especially in young boys, causing two deaths. Recurrent reactions and hidden exposure – like in a sauce or as a thickener – were most common with goat or sheep milks and cheeses, followed by peas and lentils, buckwheat and pine nuts.

Off the back of this, the team has suggested these four food types be added to the list of mandatory warning labels in Europe, which states the presence of these ingredients must be emphasised, for instance, by being written in bold on the packaging.

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“Our main goal is to protect allergic consumers and ensure they have access to clear information,” says Sabouraud-Leclerc. “This is all part of good patient care: diagnosis, education, emergency kits and knowing how to read labels.”

While the data came mainly from France, Belgium and Luxembourg, the results would probably be applicable to other countries, with some differences in prevalence depending on local cuisine, says Sabouraud-Leclerc. “If we manage to update the EU list, that might inspire other countries to follow, kind of like a snowball effect,” she says.

Adults with peanut allergy reduced their risk of reactions by eating a little peanut protein every day as part of a trial. This approach is already approved in the US for children with the condition.

Peanut allergy occurs when the immune system mistakenly identifies proteins in the legume as a threat. It responds by producing more IgE antibodies, which are a vital part of the immune response, but go into overdrive with allergic reactions. As a result, inflammation ramps up, causing symptoms such as swelling, itching and vomiting. In extreme cases, it can lead to anaphylactic shock, a life-threatening reaction that can affect someone’s breathing or their heart rate.

Until recently, the only solution was to avoid peanuts, but an intervention called oral immunotherapy was approved for children with the allergy in the US in 2020. This involves training the immune system to tolerate the allergen by exposing it to gradually increasing doses of peanut proteins.

However, it was unclear if the approach also worked in adults. “Most of the life of a peanut allergic individual is spent as an adult, but we’ve had no treatment to reduce their underlying reactivity to peanuts,” says at King’s College London. “There are some grounds for suspecting that adults would be more hard to desensitise than children because your immune system is easier to modify when you’re younger.”

To fill this knowledge gap, Till and his colleagues recruited 21 adults with peanut allergy. At the start of the study, the participants were only able to eat up to an eighth of a peanut, on average, before having an allergic reaction.

The team had each participant eat the protein equivalent of one 40th of a peanut every day for two weeks. This dose was slightly increased every two weeks for several months, until they could safely and consistently eat the protein equivalent of four large peanuts every day for a month.

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Three participants dropped out of the study due to allergic reactions, while three others left due to reasons unrelated to the treatment. “This dropout number is acceptable for this kind of treatment,” says at the Swiss Institute of Allergy and Asthma Research.

The remaining 15 participants took part in an allergy test where they ate increasing doses of peanut protein under the researchers’ supervision. All but one of them was able to eat the equivalent of five peanuts without having an allergic reaction.

In another part of the experiment, the team analysed blood samples collected from the participants before and after they received oral immunotherapy. This revealed that the intervention caused them to have higher levels of IgG antibodies, which counteract the effects of IgE antibodies.

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“It is very promising,” says Akdis. “This approach could mean that adults with peanut allergy can be relieved of the anxiety of eating food contaminated with peanuts.”

But this was a relatively early-stage trial, and larger ones are needed to verify the results and establish how long the protection lasts, he says. “I’d expect you’ll need to take daily or regular doses of peanuts in the long term to maintain the tolerance to the allergen,” says Akdis. “People take pills every day, so I think people affected by peanut allergies may well be fine adhering to this sort of method.”

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There is no strong evidence that people with peanut allergies are at risk of a severe reaction from others eating peanuts and the allergens circulating through the air while on board a plane. While peanuts are technically legumes, it is thought the findings will also apply to nuts and other foods that people are commonly allergic to.

People with food allergies may experience symptoms such as rashes, nausea and breathlessness after being exposed to allergens through eating, skin contact or inhalation. In severe cases, this can cause a life-threatening reaction called anaphylaxis, which can lead to swelling of the throat, dizziness and more serious breathing difficulties.

Some airlines have banned the sale of nuts on flights and their staff make announcements asking passengers not to eat them if they know someone on board has an allergy.

To explore the evidence behind the inhalation risk, at Imperial College London and his colleagues focused on peanuts, reviewing the results of five studies.

One study looked for peanut particles in air samples during a commercial flight where the snack was being served. The researchers found none in nearly all the samples they collected. That is because these aircraft have filters that remove peanut particles in the air before they spread through the cabin, says Turner.

The exception was air samples collected immediately around tray tables where peanuts were being consumed, but these allergens were at such low levels that they would probably be insufficient to cause an allergic reaction, says Turner.

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Four other studies looked at airborne allergen levels as people ate or shelled peanuts, either in their homes or a lab. They similarly found very low levels of allergens within about half a metre of someone shelling or eating peanuts. At most, this would cause mild allergic reactions, such as watery eyes, says Turner.

But higher levels of allergens were found on seats, trays and the floor of the first study’s aircraft. Wiping down these surfaces would probably remove much of the risk, says Turner, whose team is working with UK airlines to make flying safer for people with allergies.

The same results would probably apply to other allergens, such as nuts, seafood and eggs, says Turner.

“This report summarises what has been well established for years, in that peanut is highly unlikely to aerosolise and pose an airborne risk to passengers,” says at the University of Colorado.

A toothpaste infused with peanut proteins could help to prevent serious reactions in people with a peanut allergy. The treatment has passed a safety trial in adults, with the researchers now hoping to test how effective it is among children with the allergy.

Peanuts are one of the most common allergy-causing foods, affecting millions of people in the US and UK, says at the University of California, Irvine. “There’s a real unmet medical need and, other than avoidance, there are very few treatments available,” he says.

In a bid to fill that gap, Berger and his colleagues have developed a toothpaste that contains peanut proteins, in the hope it could train someone’s immune system to tolerate the food.

To test its safety, the team enlisted 32 adults with a peanut allergy. Of those, 24 were asked to use the peanut toothpaste, while the rest were given the same toothpaste but without the peanut proteins, acting as a placebo. All of the participants were instructed to brush their teeth every morning for 2 minutes with a pea-sized amount of either the peanut or placebo toothpaste, and to use their usual toothpaste in the evening.

At the start of the study, the peanut toothpaste contained just 1 milligram of peanut proteins per pea-sized dose, which was gradually increased over the 48-week trial to 80 milligrams – equivalent to the amount found in a third of a typical peanut.

The study – which will be presented on 11 November at the American College of Allergy, Asthma and Immunology’s meeting in Anaheim, California – found that none of the participants experienced any moderate or severe reactions to either toothpaste. About half of those in the peanut-toothpaste group reported temporary itching in their mouths, which didn’t occur in the placebo group.

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Berger told żěè¶ĚĘÓƵ that at the end of the 48 weeks, three of the participants in the peanut-toothpaste group were exposed to 300 milligrams of peanut proteins. None of them experienced any degree of allergic reaction, he says.

Having shown its safety, the team hopes to further test the toothpaste’s effectiveness in around 80 children. “We hope to see efficacy because children typically have a stronger immune response than adults,” says Berger.

Berger believes toothpastes could have potential as a unique way of preventing allergic reactions, given that people use them as part of their daily dental hygiene routine, he says.

Consuming a fat molecule produced by gut bacteria may prevent mice with severe peanut allergies from experiencing a life-threatening immune reaction. The findings suggest the approach could prevent this anaphylaxis reaction in people with food allergies and it could even prevent people developing allergies in the first place.

Anaphylaxis commonly involves nausea, abdominal pain and impaired breathing or trouble swallowing. Over the past decade, researchers have found that a fat molecule called butyrate, which is produced by gut bacteria, can reduce these allergic reactions in mice. People with food allergies also seem to have less butyrate-producing bacteria than non-allergic people do, suggesting that boosting butyrate could help them.

However, butyrate can smell like dog faeces or rancid butter, making it unpleasant to swallow. What’s more, when taken orally, it breaks down before reaching the lower gut where its beneficial effects take place.

Now, at the University of Chicago in Illinois and his colleagues have developed a way to mask the foul smell of butyrate and deliver the molecule to the lower gut, by packaging it within spherical capsules called micelles that are up to 30 nanometres wide. “We developed this drug delivery platform, polymeric micelles, to deliver butyrate to the gut to treat food allergies,” says Cao, who presented the work at a meeting of the American Chemical Society in Chicago on 21 August.

The researchers treated 80 mice with an antibiotic to reduce their levels of butyrate-producing gut bacteria, then gave them severe peanut allergies by giving them peanut protein along with an immune-stimulating toxin for 4 weeks. They then gave the micelles to half the mice twice a day for two weeks, with the other half receiving a saline solution as a control, before feeding all of the animals 1 milligram of peanut protein.

While the control mice developed anaphylaxis from the peanut protein, as measured by a drop in their core body temperature and increased immune activity, the mice that received the micelles didn’t. “It was a very exciting moment when we saw the results, that the butyrate prevented anaphylaxis,” says Cao.

By analysing the bacteria in the mouse faeces before and after treatment, the team then found that the butyrate-carrying micelles boosted the growth of butyrate-producing bacteria, suggesting that the treatment could alter the gut microbiome to produce more of its own butyrate.

“We’re aiming for creating a niche for those healthy bacteria to grow using this treatment, so that the micelles don’t need to be taken for a very long time,” says Cao.

The researchers also hope that the treatment can be used to prevent people developing many types of food allergies in the first place. “The approach should work on any food allergen,” says Cao. “We imagine the micelles could come in a packet, and you just add it to a glass of water.”

“Short-chain fatty acids [like butyrate] could absolutely prevent food allergy,” says at Monash University in Melbourne, Australia. “This work may have a huge impact if the treatments work in humans. We need to do the trials and I am very optimistic. Existing treatments are crude and unconvincing.”

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