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?
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.
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.