I recently discovered that - like 5% of asthmatics apparently - I am sensitive to sulphites. Aka 'sulfites'.
If I consume food or drink containing sulphites, which are widely used as preservatives, I get sick. Generic feeling very rough plus asthma, naturally.
I've only just found this out, so I wondered if anyone else had any thoughts or expeirences to share.
For those who think this may be worth examining, a simple first step is Wikipedia's article.