BROADLY speaking, East Asians and Westerners suffer the same types of food allergies in about the same proportions. But there is an exception. Westerners are roughly twice as likely as East Asians to be allergic to peanuts. This is a puzzle—as is the question of why anyone is allergic to peanuts in the first place.

A paper in the Journal of Allergy and Clinical Immunology sheds light on both matters. The study it describes, conducted by Quentin Sattentau of Oxford University and his colleagues, found that mice are more likely to develop a peanut allergy in response to dry-roasted nuts than raw ones. Since dry roasting is more common in the West than in East Asia, that may explain the disparity of incidence. And the chemical changes induced by dry roasting help explain what causes peanut allergy in the first place.

Dr Sattentau and his team injected their mice with proteins derived from raw or dry-roasted peanuts, to prime the animals’ immune systems. Then, they fed those animals raw or dry-roasted peanuts. Mice that had been primed with proteins from the dry-roasted nuts exhibited more robust immune responses to both diets. Their levels of antibodies—specifically of a type called immunoglobulin E (IgE)—rose significantly. High levels of IgE are the hallmark of an allergic reaction. Though the mice primed with raw-peanut protein also produced lots of antibodies, far fewer were IgEs.

The difference, Dr Sattentau thinks, stems from the fact that dry roasting triggers what is known to chemists as the Maillard reaction, and to chefs as “browning”. The Maillard reaction is one between sugars and proteins that forms new, complex molecules called advanced glycation end-products (AGEs). These create many of the pleasant aromas associated with cooked foods, but are also suspected of causing certain allergies—including, it would now appear, peanut allergy.

Indeed, Dr Sattentau showed that proteins derived from dry-roasted peanuts bind to dendritic cells, a type important to the immune response. Specifically, these proteins interact with cell receptor-molecules known to bind to AGEs. Dr Sattentau believes this binding is the molecular mechanism which triggers peanut allergy.

Don’t go nuts

Why, even so, most people can eat peanuts without ill effect, is probably a quirk of genetics. The genes that regulate the immune system are the most variable in the human genome so, peanutwise, some people are probably just dealt an unlucky hand by the genetic shuffling that created their own genomes out of their parents’.

But for those people—and particularly for those among them for whom even proximity to peanuts risks anaphylactic shock—there is reason for hope. Results of an experiment published earlier this year by researchers at Cambridge University showed that exposing peanut-sensitive children to tiny amounts of the nuts can, over a period, slowly desensitise them. If this finding holds up it could mean that, though those who develop peanut allergy may never enjoy the things in the way that the rest of humanity does, at least effects of peanuts on them will be peanuts.