I think allergies are possible with just about anything. And with mushrooms specifically, well. . . I read a report on erowid where a guy got hives or something after taking shrooms.
Well, not to say you should base your opinion on my experience... But I've taken extensive allergy testing in my life, and i'm allergic to pretty much everything but dogs and grass. I've never had a problem with shrooms.
i knew a dude that was allergic to just plain mushroom. he didnt tell me of course untill AFTER the trip to the hospital-- not fun! so this dude was allergic to all mushrooms anyway-so you would probably already know it if you werew