What Is Sodium Metabisulfite and Why Is It in Food?

You've probably encountered many products containing sodium metabisulfite without even realizing.

It's often used in commercial food preservation and wine making, according to a September 2019 study in the ‌European Journal of Clinical Nutrition‌ (EJCN). Though sodium metabisulfite is a common food additive, for some people, it can cause negative side effects.

Sodium metabisulfite is a type of sulfite additive. It is used as a preservative and antioxidant to prevent browning and discoloration during food preparation and distribution, according to the Cleveland Clinic. It is often found in wine and dried fruits.

Sodium metabisulfite is also commonly used in a number of other industries, not just food and beverages. It's used as a general bleaching agent in the textile, pulp and paper industries, according to the National Center for Biotechnology Information (NCBI). It also has uses in the chemical, pharmaceutical, film and photographic industries, and even in water and sewage treatment plants.

On its own, pure sodium metabisulfite can actually be hazardous. The powder is highly irritating to skin and tissue and is toxic to inhale, per the NCBI. It's also corrosive when mixed with water.

As a food preservative, sulfites — including sodium metabisulfite — can cause respiratory symptoms for some people, particularly people with asthma. Sulfites can cause wheezing, chest tightness and coughing in 5 to 10 percent of people with asthma, according to the Australian Society of Clinical Immunology and Allergy (ASCIA).

These symptoms are more likely to occur if a person's asthma is poorly controlled. And sulfite-related respiratory symptoms can also happen in people with no history of asthma, per the ASCIA.

The range of sulfite reactions can be quite broad, says Bonnie Taub-Dix, RDN, founder of BetterThanDieting.com and author of ‌‌Read It Before You Eat It: Taking You From Label to Table‌‌.

"[Sulfites may cause] a slight intolerance for one person but a severe allergic reaction for another — they are really vastly different," she says. "If you have an intolerance to something, you probably could eat a small quantity without it being much of a problem." However, some people may have severe sulfite reactions, including difficulty breathing.

Most sulfite reactions happen due to inhaling the sulfur dioxide generated from sulfite-containing foods or drinks, according to the Cleveland Clinic. For example, beer and wine contain sulfites and the sulfur dioxide is inhaled as you drink.

In very rare cases, sulfites can cause an allergic reaction called anaphylaxis, per the ASCIA. The symptoms of anaphylaxis include shortness of breath, chest tightness, hives, swelling of the face, lips or tongue, hay-fever like symptoms (like runny nose and watery eyes), throat tightness or difficulty swallowing, according to Food Allergy Canada. Other symptoms can include stomach discomfort, fast heartbeat, dizziness or passing out.

Additionally, the small September 2019 ‌EJCN‌ study found young adults who are already susceptible to wine-induced headaches had a higher risk of getting a headache after drinking wine with greater sulfite concentration compared to wine with lower sulfite concentration.

Sulfites in food actually used to be much more common. But a number of cases of severe reactions in the 1970s and '80s prompted the Food and Drug Administration (FDA) to prohibit their use in fresh fruits and vegetables, per the Cleveland Clinic.

Today, sulfites are permitted in foods such as beer, wine, shrimp and potatoes. Sulfites are also found in dried fruit, syrups, jams, jellies, breads and pizza dough, according to the ASCIA.

Though sulfites are common in foods and drinks, if you're sensitive, there are ways to avoid them. The Cleveland Clinic recommends reading food labels and avoiding foods that contain the following:

• Sulfur dioxide
• Potassium bisulfite
• Potassium metabisulfite
• Sodium bisulfite
• Sodium metabisulfite
• Sodium sulfite

If you're concerned about sulfites in wine, look for wines that say "no sulfite" or "sulfite-free."

Taub-Dix says it's important for each individual to learn how their body responds to certain foods and additives. However, rather than experimenting with food reactions on your own, if you think you have a food sensitivity or allergy, Taub-Dix says it's best to consult an allergist or your primary care doctor.