"Allergy or preference?" is an interesting question. For many people the answer would be neither: they suffer physical pain if they eat a significant amount of wheat - half a slice of bread might be enough to produce symptoms, for example - but it's not technically an allergy and it's not life-threatening. You don't need to use different equipment for these people, but you should carefully check the list of ingredients.
I wasn’t aware an allergy had to be life-threatening to be classified as such. In fact, double-checking with a dictionary confirms it isn’t defined that way.
I grew up allergic to chlorine (swimming pools). The allergic reaction was/is eczema. This was not life threatening. For the past 12 years I’ve suffered from pollen allergy annually. Also not life-threatening.
