It wasn't a special occasion—or even a fancy restaurant—but Karen, 37, will never forget that meal. She described her experience:

"My boyfriend and I were at a hamburger joint, and I had a burger and fries. About 10 minutes after we finished eating, my throat began to itch. I grabbed my [asthma] inhaler but I could feel my throat constricting. I couldn't breathe and started to panic. When I passed out, my boyfriend flagged down a passing police car. The officer radioed for an ambulance, and I was rushed to the hospital. I was revived with a massive dose of epinephrine to counteract the reaction caused by the sulfite solution the potatoes had been soaked in before frying.

"I know enough to stay away from wine, shrimp, and other foods that contain sulfites, and take note whenever I don't feel right after eating something. But I never expected french fries to be sulfited. I've had allergic reactions to sulfites before, but this time I came close to dying.

"I was angry that this happened to me. I felt powerless—I was careful and knowledgeable, and yet I couldn't protect myself. Who ever heard of a lethal french fry? Afterward, I refused to eat out in restaurants for almost two years, and I still can't visit people or go on vacation without knowing there is a hospital nearby."

The Food and Drug Administration (FDA) estimates that one out of a hundred people is sulfite-sensitive, and that 5% of those who have asthma, like Karen, are also at risk of suffering an adverse reaction to the substance. "By law, adverse reactions to drugs must be reported to FDA by doctors or pharmaceutical companies. But with sulfites and other food ingredients, reporting is voluntary, so it's difficult to say just how many people may be at risk," cautions FDA consumer safety officer JoAnn Ziyad, PhD.

Testing for Sulfites

Complicating matters, scientists have not pinpointed the smallest concentration of sulfites needed to provoke a reaction in a sensitive or allergic person. The FDA requires food manufacturers and processors to disclose the presence of sulfiting agents in concentrations of at least 10 parts per million (ppm), but for some persons, symptoms could occur at concentrations even below this threshold. Since the assay used to detect the level of sulfites in food is not sensitive enough to detect amounts less than 10 ppm in all foods (that's one part sulfite to 100,000 parts of food—the equivalent of a drop of water in a bathtub), the regulation has to be based on measurements that are actually possible, explains Ziyad.

"The most rapid reactions occur when sulfites are sprayed onto foods or are present in a beverage, but the most severe reactions occur when sulfites are constituents of the food itself," says Ron Simon, MD, head of Allergy, Asthma, and Immunology at Scripps Clinic and Research Foundation in La Jolla, California.

A person can develop sulfite sensitivity at any point in life, and no one knows what triggers onset or the mechanism by which reactions occur. "Doctors believe that asthmatics develop difficulty breathing by inhaling sulfite fumes from treated foods," notes Dan Atkins, MD, a pediatrician at the National Jewish Center for Immunology and Respiratory Medicine in Denver, Colorado. He says that in a severe reaction an overwhelming degree of bronchial constriction occurs, causing breathing to be completely obstructed. This can lead to lack of oxygen reaching the brain, heart, and other organs and tissue and, possibly, a fatal heart rhythm irregularity.

Diagnosing Sulfite Sensitivity

"We now know that asthmatics who have more severe symptoms and are dependent on corticosteroids, such as prednisone or methylprednisolone, are especially prone to sulfite sensitivity and are most at risk of having a severe reaction," notes Atkins. But it's a chicken-and-egg situation, notes Simon: "We don't know which comes first, the asthma or the sulfite sensitivity. Because some people's first experience with asthma is a sulfite reaction and as their asthma becomes more severe, they eventually become steroid-dependent."

Sulfite sensitivity can be tricky to diagnose. Karen went to an internist and two pulmonary specialists without getting to the bottom of her problem.

"People who do experience adverse reactions to sulfites know that it's something they ate, but might not know what that something is," says Atkins. "I'll ask a patient complaining of an adverse reaction what he or she ate and drank when it occurred. If beer or wine doesn't seem to be the problem, I tend to dismiss sulfite sensitivity. But if I think sulfites may be the culprit, I'll do a challenge [a type of allergy test in which a small amount of the suspect substance is administered in a capsule or in a drink and the patient is monitored to see whether there is a reaction]."

If a person develops hives after ingesting sulfites, the doctor will do a prick test. (A small concentration of sulfite is placed on the skin, which is then pricked; the test is positive if a welt develops on the spot). "People who have positive skin tests to sulfites are likely to be allergic to the additive, rather than have a sensitivity. These people, who are usually not asthmatic, are most at risk of anaphylactic shock [a life-threatening reaction]," says Simon.

How Sulfites Are Used

Sulfur-based preservatives, or sulfites, have been used around the world for centuries to:

  • Inhibit oxidation ("browning") of light-colored fruits and vegetables, such as dried apples and dehydrated potatoes
  • Prevent melanosis ("black spot") on shrimp and lobster
  • Discourage bacterial growth as wine ferments
  • Condition dough
  • Bleach food starches
  • Maintain the stability and potency of some medications.

The FDA has taken the following actions to restrict sulfite use:

  • Prohibited the use of sulfites to maintain color and crispness on fruits and vegetables that are meant to be eaten raw (for instance, restaurant salad bars or fresh produce in the supermarket)
  • Required companies to list on product labels sulfiting agents that occur at concentrations of 10 ppm or higher, and any sulfiting agents that had a technical or functional effect in the food (for instance, as a preservative) regardless of the amount present (This labeling requirement was extended to standardized foods, such as pickles and bottled lemon juice, in 1993.)

The FDA requires that the presence of sulfites be disclosed on labels of packaged food (although manufacturers need not specify the particular agent used). This information will be included in the ingredient portion of the label, along with the function of the sulfiting agent in the food (for instance, a preservative).

When food is sold unpackaged in bulk form (as with a barrel of dried fruit or loose, raw shrimp at the fresh fish counter), store managers must post a sign or some other type of labeling that lists the food's ingredients on the container or at the counter so that consumers can determine whether the product was treated with a sulfiting agent.

"The ultimate goal of sulfite regulation is to make sure that there is no higher level of sulfite residues in food than is absolutely necessary and to encourage the use of substitutes for sulfites in food processing," says Ziyad.

Sniffing Out Sulfites

The FDA's Adverse Reaction Monitoring System has been tracking reactions to sulfites since 1985. Over a 10- year period, 1,097 such cases have been reported. However, perhaps due to regulatory action taken by the FDA over the years, coupled with increased consumer savvy, the number of reported sulfite-related health incidents has been dropping steadily. In 1995, just six cases were reported, and between 1996 and 1999 only an average of ten reports of sulfite reactions were received yearly.

Since the FDA banned the use of sulfites on fruits and vegetables that are to be eaten raw (as with a salad bar)—the vast majority of those in the food service industry honor the prohibition. However, consumers who are sulfite-sensitive "shouldn't take anything for granted," says Ziyad.

Current FDA regulations do not require managers of food service establishments to disclose whether sulfites were used in food preparation. "Consumers continually request the FDA to extend the regulation to include food service establishments because either waiters or other staff members didn't know whether the food was treated with sulfites, or gave erroneous information," notes Ziyad. "The FDA's position on the issue has been that consumers who see sulfites listed on the label of a packaged food should be able to deduce that the same food sold in a food service establishment would also contain sulfites," she explains.

In addition, sulfites are still found in a variety of cooked and processed foods (including baked goods, condiments, dried and glacéed fruit, jam, gravy, dehydrated or precut or peeled "fresh" potatoes, molasses, shrimp, and soup mixes) and beverages (such as beer, wine, hard cider, fruit and vegetable juices, and tea).

Since sulfites are added to so many foods, someone who is sensitive to the additive must not assume that a food is safe to eat, says Atkins. He recommends the following measures to avoid sulfites when buying unlabeled foods at the deli or supermarket and ordering at a restaurant:

  • If the food is packaged, read the label. 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. Similarly, if you've experienced a severe reaction to sulfites in the past (such as breaking out in hives), carry an antihistamine and make sure you have handy a self-administering injectable epinephrine, such as EpiPen, so that if you have a reaction you can stabilize your condition until you get to an emergency room.

"It takes some doing, but you can take steps to minimize your contact with sulfites if you are diagnosed with asthma or sulfite sensitivity," says Ziyad. "But you may not even know you have a problem with sulfites until a reaction occurs. Undiagnosed people are at risk because even if they know that sulfites can cause adverse reactions, they often don't associate sulfites with their own health problems," says Ziyad.

"Regulations can go a long way towards protecting people, but there's no substitute for knowledge."