From the Super Mario Wiki
Retrieved from "https://www.mariowiki.com/index.php?title=Allergic&oldid=2508764"
Allergic is a status ailment that only appears in Paper Mario: The Thousand-Year Door. If afflicted by this Mario and/or his partner will no longer be able to be inflicted with further status ailments, neither positive nor negative. However, it will not remove status ailments that are already applied. This also means that they cannot use status-raising items or the Star Power Power Lift. As such, it is the only neutral ailment in the Paper Mario series. It is indicated by a small universal "No" symbol above the afflicted.
Mario and his partners can only attain this status through eating Space Food or being hit with the Shadow Queen's Dangerous Breath attack, thus making it one of the rarest status ailments in the game.