If it is being sold loose or by the portion, ask the store manager or waiter to check the ingredient list on the product's original bulk-size packaging. Avoid processed foods that contain sulfites, such as dried fruits, canned vegetables, maraschino cherries, and guacamole. If you want to eat a potato, order a baked potato rather than hash browns, fries, or any dish that involves peeling the potato first. If you have asthma, have your inhaler with you when you go out to eat. But you may not even know you have a problem with sulfites until a reaction occurs.
Regulations can go a long way towards protecting people, but there's no substitute for knowledge.