Dietary allergies are almost always to proteins, because proteins are complicated structures the body can recognize as foreign. The immune system just doesn’t care about carbs or lipids as much (with some exceptions.) So, protein-rich foods are the main culprits. In the U.S., the list of common food allergies is typically “milk, eggs, tree nuts, peanuts, shellfish, wheat, soy, fish.” [To clarify, milk allergy here is milk protein allergy, not lactose intolerance; wheat allergy here is distinct from celiac disease or gluten intolerance.]
Looking at it this way, it’s less odd, really just a list of common sources of protein. Peanuts stand out in the U.S. because they’re such a common food, and one frequently introduced to children around an age when allergies might develop (in Israel, where peanut snacks show up earlier in childhood, allergy rates are lower, though there are other potential differences at play.) Worldwide it’s not one of the leading allergies.
Perhaps the more interesting question would be “why are meat and poultry allergies rare?”
By the way, the main reason there are “a lot” of peanut allergy sufferers today is linked with bad science from 20 years ago: [https://www.preventallergies.org/blog/why-are-peanut-allergies-on-the-rise](https://www.preventallergies.org/blog/why-are-peanut-allergies-on-the-rise)
Basically, someone recommended that we NOT introduce peanuts to babies and young children in order to avoid allergic reactions, and it made everything worse.
>But in the late 1990s and early 2000s, doctors changed their approach.
They mistakenly thought that delaying the feeding of peanut for several
years was the best approach to preventing peanut allergies.
Uh-oh!
>But when these recommendations to delay feeding peanut were introduced,
there was no study to support these recommendations. Rather, they were
just based on physicians’ guesses.
Whoops!
>Today, we know that this approach to delay peanut introduction actually increases food allergy risk, and that delayed introduction was a major factor that led to the sharp increase in peanut allergies.
>
>Thanks to landmark clinical studies, we now know that the opposite approach—feeding baby peanut early and often, before they turn one—is the best way to prevent peanut allergies.
Whew!
(sound effects added for the 5-year-old)
Assuming the correct interpretation of your question is “of the people with allergies, why are peanuts the most prevalent”, that’s likely a false assumption and/or is regional based.
In the US, [the most prevalent allergy is shellfish (based on a 23 year old study)](https://pubmed.ncbi.nlm.nih.gov/10200001/) by far, at over 50% more common than the next two on the list – milk and shrimp. Peanuts are pretty high on the list, but are only number 4.
That said, why does it *seem* so common? Probably because peanuts have a great shelf life and don’t need to be refrigerated or prepared after packaging to be safe to consume. You can buy peanuts, open them, and they stay safe for a month or longer at room temperature (how long really depends on where you look). Packaged and refrigerated they can last a year or so. Shellfish, milk, shrimp? Those all have a much shorter shelf life and need refrigeration.
So with those above considerations, it’s significantly easier to find peanuts in all sorts of scenarios, whereas the more common US allergies are only really found in kitchens or restaurants. So even though peanuts aren’t the most common food allergy in the US, they’re easily the most common to be found outside of homes/restaurants….where it’s harder for people with such allergies to avoid them.
They’re also dry and shed dust which can trigger the allergy long past the presence of actual peanuts.
tl;dr – Peanuts are *not* the most common allergy (in the US at least), but they’re much easier to be exposed to than the more common allergies so it’s easier to trigger a peanut allergy in significantly more situations.
One thing I haven’t seen addressed is why allergies are becoming more prevalent.
I’m going from memory here, so correct me if I’m wrong.
One reason that peanut allergies in particular appear to be increasing is the increase in testing in children, and avoidance. Before testing was prevalent, a greater proportion of those with allergies went undiagnosed and through exposure, developed a tolerance to the allergen over time as they developed from childhood into adulthood.
When we started diagnosing more, the medical advice was to avoid the allergen completely. However this prevented many that would have developed a tolerance through gradual exposure from doing do. This is dangerous, because the severity of reactions is higher in the unexposed, which has been linked with increasing mortality rates from things like peanut allergies in adults.
Exposure therapy is becoming more widespread in those diagnosed with things like peanut allergies as a consequence.
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