# What is an Allergen? **URL:** \ **Category:** Factual Questions\ **Created:** [September 25, 2013, 4:42pm UTC](https://boards.straightdope.com/t/what-is-an-allergen/669656 "2013-09-25T16:42:46Z")\ **Posts on this page:** 1\ **Showing post:** 9
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [September 26, 2013, 7:31am UTC](https://boards.straightdope.com/t/what-is-an-allergen/669656/9 "2013-09-26T07:31:54Z")
In any case, I think the underlying statement (the one I originally challenged, quoted below) is false, on two levels. 1. It appears there are mechanisms by which exposure to smoke or other non-protein-based substances _can_ result in an allergic outbreak. 2. (Off topic for this thread, but not the hijack to the other one) Regardless of the precise mechanism, or even the precise type of reaction, responding to the question “may I expose you to chemical X?” with “Please don’t - I’m allergic” is still a sensible and reasonable response. The waiter does not need to understand or care that your aversity to shellfish is actually because of an _intolerance_. The person offering you a glass of sulphited wine does not need to know or care that the sulphite releases Sulphur Dioxide, which is then a factor in a chain of events, leading to anaphylaxis. “No thanks - I’m allergic to it” is probably the right thing to say. > [@Responding to the polite "non-question"](https://boards.straightdope.com/t/responding-to-the-polite-non-question/669384/32): > > You may want to avoid using that excuse considering cigarette smoke can’t actually cause an allergic reaction as it lacks any protein to cause an immune system response. --- _[View the full topic](https://boards.straightdope.com/t/what-is-an-allergen/669656)._