An experimental immunotherapy treatment that introduces peanut protein in small doses to those who suffer peanut allergies to desensitize their immune system may actually increase risk of anaphylaxis, a new study has shown.

More than 50 million people in the US suffer from allergies – an overreaction by the immune system to a substance that doesn’t affect most other people – and this is on the rise. Some are harmless, some go away as you get older, and some are both life-long and life-threatening, like nut allergies.

Around 8 percent of children and 4 percent of adults suffer a food allergy, causing 200,000 emergency room visits a year. There are currently no FDA-approved treatments to either prevent or reduce food allergy symptoms, and for peanut sufferers particularly, the only option is to vigilantly avoid the nut and carry an epinephrine injector at all times.

Oral immunotherapy treatment is an emerging experimental treatment that attempts to desensitize the immune system over time by repeated, increasing doses. The aim is not necessarily to eliminate the allergy but to reduce the likelihood that accidental exposure may become fatal. In clinical trials, it has been deemed successful as patients undergoing treatment have passed supervised food challenges with no reaction.

However, a review of 12 studies with more than 1,000 patients who were followed for one year after treatment has found that this very treatment considerably increases allergic and anaphylactic reactions rather than preventing them.

Their results, published in The Lancet, found that those who were treated with peanut oral immunotherapy had a 22 percent risk of anaphylaxis compared to a 7 percent risk for those who hadn’t received treatment – that's three times more likely. Sufferers were also 8 percent more likely to use their EpiPen if they’d had the treatment, twice as likely as those who hadn’t.

Importantly, the researchers are not claiming the treatment doesn’t work, as it has clearly been shown to in clinical settings, but that their review instead highlights the gap between results in a clinical setting and real-life applications.

There is even a suggestion that the way the treatment is carried out – patients are told to avoid exposure to peanuts except for their doses – may contribute to the increase in allergic reactions in the real world. The researchers also note that passing a food allergy test in a controlled environment may not be the best way to predict a person’s future allergy risk in a real-world setting. 

"This protection that you get from going through immunotherapy – that can change every day," lead author Dr Derek Chu, who himself has a peanut allergy, told CNN. "If you exercise within two to four hours, or you take a hot shower, or you have an empty stomach, that can all change the way your body interacts with the food that you've supposedly been desensitized to." 

There are caveats to the review, the sample size was small and patients were only followed for a year, but the more we know about immunotherapy treatment the better we can make not only the treatment but the trials designed to test success. In the meantime, patients can make better-informed decisions about the benefits and risks of peanut oral immunotherapy.