Celery allergy?

Recently I’ve noticed quite a few foods bearing the warning “Contains celery”, along the lines of “Contains peanuts”. I thought that a bit strange - surely people aren’t allergic to celery? - but a quick look on Wikipedia confirms that celery can indeed be a potentially serious allergen. (And there was I thinking that maybe celery was considered taboo by scientologists or something.)

So is celery allergy really a big problem? Is it the seeds in particular that can be dangerous? Celery stalks seem pretty innocuous things - almost entirely water and cellulose. Does anyone here suffer from celery allergy or know someone who does?

Celery is a member of the Umbelliferae - lots of plants in this family contain poisonous and irritant compounds (Hemlock, for example), indeed wild celery contains compounds that can provoke - amongst other symptoms - rashes and skin photosensitivity, Cultivated varieties have diminished levels of these compounds, but they’re probably still present in trace - and that’s all it takes to trigger an allergy in some people.