Allergic means reacting badly to a substance that most people tolerate perfectly well. The immune system attacking the wrong thing.
It takes to. The reactions run from a rash to anaphylaxis, which is a medical emergency, and that is why food labelling and school policies take it so seriously. Being allergic to something is a diagnosis rather than a preference, which matters, because dismissing it as fussiness has killed people. There is a jokey figurative use, as in being allergic to hard work.
1adjectiveallergicHaving a harmful immune reaction to a particular substance.
“He is severely allergic to peanuts.”
German
Allergie
English
allergy
English, today
allergic
Built from
From allergy + -ic. allergy Borrowed from German Allergie. Borrowed from German Allergie. Coined by Austrian pediatrician Clemens von Pirquet in 1906 from Ancient Greek ἄλλος (“other”) + ἔργον (“work, activity”), on the model of Energie.
Etymology from Wiktionary, CC BY-SA