A 2004 study by Simonte et al. exposed 29 severely peanut allergic patients to a double-blind inhalation challenge to 3oz of peanut butter (or soy butter, both masked for smell) just 12 inches from the nose. As well, a pea sized drop of either masked butter was smeared on the skin for 1 minute, and then was removed. In both exposures, no one developed any allergic reactions. There were 3 patients who developed localized erythema and 5 developing localized pruritus from the peanut butter skin contact, but 5 also developed erythema with soy butter skin contact, which demonstrates that butters on the skin can cause irritation but not generalized reactions. The authors concluded that casual contact or inhalation of peanut butter was highly unlikely to cause any symptoms.

In 2016, Jin et al re-replicated these findings within a cabin of an airplane in flight. They noted surface contamination of Ara h 2 on unwashed tray tables after someone ate peanut over them, and among 7 air filters measuring Ara h 2 content when placed on a tray table directly below the mouth of someone eating peanut only 1 filter detected any level, which was 1-2ng/500cm3. They found no detectable peanut levels from 3 air filters tested in a restaurant where individuals were deshelling and eating peanut. Investigators concluded that the risk of exposure to peanut on an airplane stems from potentially contaminated surfaces and not from airborne levels.

https://www.aaaai.org/Allergist-Resources/Ask-the-Expert/Answers/Old-Ask-the-Experts/peanut-air-travel