This is why you don't get nuts when traveling on an airplane carrying a passenger with a nut allergy. Allergic responses vary wildly. You might have a mild allergy that gives you a rash if you eat too much of something. Or, you might go into anaphylactic shock if you breath air that's had nuts in it.

My wife has an autoimmune disease that's triggered by foods. Some foods more than others, and there's some tolerance to each. She shouldn't eat capsicum, but she loves spicy food, and she can eat some, but it she eats it too often, she gets a response flare. OTOH, she can't have any amount of dairy: the response is rapid, and severe, and she has to take steroids to get it under control. Luckily, she's not sensitive to anything (that we've found, anyway) that triggers a response from the molecules in the air.

Oh, there are two things you may have forgotten: first, when you smell something, you're literally tasting molecules of that thing; second, your skin is your body's largest organ, and you can absolutely ingest stuff through your skin. That's how Novichok, and other nerve agents, work.

Gluten intolerant person here. It's like any other allergies where it runs the gambit. Most of us only have digestive issues if we eat it. Very rarely however, people will have the thing where they will just fucking explode into hives if someone breaks out a piece of bread in the same room as them. Just like peanut kid in elementary school.

Bro you are talking about play dough age kids here. Even if they don't stick the dough in their mouth they most certainly won't anally wash their hands after every time they play with play dough in a very defined area of the house.