Sodium bisulfite, also known as sodium hydrogen sulfite, is a white, odorless inorganic salt that is used as an additive in certain foods. In very small, microscopic quantities, sodium bisulfite is relatively benign, and the Food and Drug Administration generally recognizes it as a safe substance. However, it can cause strong reactions in some people, and food recalls due to sulfite sensitivities occasionally occur in the United States.
Sodium bisulfite — together with its related compound, sodium metabisulfite — is a minor ingredient that preserves the aroma and flavor of bottled lemon juice, dried apples, dehydrated potatoes and nearly all commercial wines. However, the FDA prohibits the use of sodium bisulfite in meats, vitamin B-1 food sources, and raw fruits and vegetables, such as in salad bars or fresh produce in supermarkets. Sodium bisulfite works by releasing sulfur dioxide gas, which inhibits bacterial and fungal growth and prevents the discoloration and deterioration caused by common chemical reactions.
Sodium bisulfite is well-tolerated by the vast majority of people. Sulfite-based compounds have not generally been found to cause cancer or birth defects in laboratory animals, even in relatively high concentrations, reports the University of Florida Institute of Food and Agricultural Sciences, and they have also tested negative for mutagenic properties. Sulfites have been important food additives since at least 1664, and they've been approved in the United States since the 1800s. They have been considered safe historically except in those who have reactions to them.
Sensitivity to sulfite-based chemicals is something that can develop at any point during a person's life. The precise mechanism is not currently known, but it may have something to do with an immune response or a deficiency in a specific cellular enzyme. An allergic reaction can occur within 15 to 30 minutes after the ingestion of sodium bisulfite. Although typically mild in nature, a reaction can cause varying degrees of dermatological, pulmonary, gastrointestinal and cardiovascular symptoms, including nausea, abdominal cramping, diarrhea, difficulty breathing, and the swelling, itching and reddening of the skin. At times the reaction can be severe. However, sulfite sensitivity is relatively rare. Estimates range from 0.05 percent to 1 percent of the population, although it includes about 5 percent of asthma sufferers. However, a 2001 study published in "Thorax" found that wine only triggers an asthma reaction in a small number of sulfite-sensitive asthmatic patients under laboratory conditions.
The Food and Drug Administration regulates sulfite-based compounds and requires companies to list on their products sulfites with a concentration of at least 10 parts per million — or concentrations that have a functional effect. This concentration is equivalent to 40 drops in a 55-gallon barrel of water. However, despite the relative lack of sodium bisulfite in foods, it can have a significant effect on people with sulfite sensitivities. Checking the label is always the most important part of avoiding adverse reactions. If you are buying unlabeled foods, you should ask the store manager or waiter to check the ingredient list on the original packaging.