According to WebMD, the only way to prevent allergic reactions from sulfites is to avoid foods that are likely to trigger them. Always read the food label looking for the ingredients sulfur dioxide, potassium bisulfite, potassium metabisulfite, sodium bisulfite, sodium metabisulfite or sodium sulfite. The FDA has banned the use of sulfites on fresh fruit and vegetables eaten raw, but sulfites can still be found in cooked or processed food.
Sulfites are added to foods to reduce spoilage from bacteria, slow discoloration and browning, and to add a bleaching effect. The FDA requires that any food item containing more than 10 parts per million concentration of sulfites include a warning label.
Common foods that contain sulfites are beer and wine, dried fruit, potato chips, canned vegetables, baked goods and tea. The amount of sulfites in each varies. About.com suggests avoiding any foods that typically contain more than 50 ppm, although people who suffer from severe sulfite allergies are recommended to stay below 10 ppm.
Sulfites are also found in medications. For example, Epi-Pens contain sulfites. However, About.com explicitly does not recommend withholding epinephrine from someone experiencing anaphylaxis, because studies do not show Epi-Pens harming people with sulfite allergies. Most asthma medications do not contain sulfites, but About.com recommends conferring with a doctor before using them.