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I've heard this claim a lot (usually by schools who take a lot of measures to prevent peanut exposure in the classrooms and lunch area, or by parents of allergic children), but is there any scientific evidence that non-contact exposure to peanuts or peanut butter would produce any significant symptoms in an allergy sufferer? If I'm eating a peanut butter sandwich on a bus, and the kid next to me is allergic, do I need to worry about him keeling over?

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    I suppose it could trigger some kind of a pavlovian response (people with peanut allergies could learn to associate the smell of peanuts with becoming sick and therefore start to feel sick when they smell peanuts). – GordonM Nov 19 '15 at 11:42
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It's basically false.

The smell of peanut butter is caused by pyrizines, which are not proteins. It is the proteins that trigger allergic reactions. So the smell of peanut butter sandwich from the next table should not cause an allergic reaction.

BUT people can have reactions when they inhale food proteins that they are allergic to. This can be seen when food is actively cooked, when powdered or crushed forms become aerosolized, or in other situations when proteins are released into the air.

Link to relevant study

The latter case generally only happens in enclosed spaces with large amounts of peanut material, such as an airplane where dozens of people are popping open peanut packets (study based on self-report) or inside a kitchen where peanut oil is being used to fry things and particles of the oil are being thrown into the air.

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    This doesn't mean it's not triggered by the smell of peanuts. It's possible that in virtually all conditions where you smell peanuts there are aerosolized proteins too. While it technically wouldn't be the odor causing the problem, the odor would still be a reliable indicator and I'd say the claim was true in that case. – William Grobman Nov 18 '15 at 18:18
  • ... Actually, no. As per the first two links, most cases where you smell peanuts don't involve the proteins, but pyrizines, and those don't trigger the peanuts. The smell is not what causes the allergic reaction, but the proteins, which can be airborne, but only in rare cases. The allergic reaction requires contact, if only with the aerosolized particles. – Sean Duggan Nov 18 '15 at 18:21
  • That's fair. It would be nice if you quoted the relevant passages from those links to address that though. When I read your answer without checking sources, it appears to merely be stating that the claim is technically false. – William Grobman Nov 18 '15 at 18:24
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    I shared @WilliamGrobman's concern. The quoted text is really saying "Absolutely true, except for a minor technicality. If you can smell it, you are in danger, even though strictly speaking the smell itself isn't the cause." BUT when you look at the empirical evidence (from the study, moderately small sample, peanut butter only), the answer is really "NO, spending ten minutes with peanut butter a foot from your face is fine". – Oddthinking Nov 19 '15 at 11:55
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    There is also the nocebo effect. If you are allergic to peanuts and you smell peanuts, you'll get an allergic reaction simply because you expect to get an allergic reaction. – John Dvorak Nov 22 '15 at 20:54

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