The Difference Between Sulfa and Sulfite Allergies

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Although "sulfa" and "sulfite" sound similar, the two chemicals are not related. Therefore, so won't necessarily be allergic to the other just because you've had a reaction to one.

Sulfites are chemicals that are often used as preservatives and antioxidants in foods (preventing browning and spoilage). A sulfa allergy refers to an allergy to sulfonamide-containing drugs (also called sulfur drugs). These drugs have a sulfonamide group in their chemical structure.

This article will discuss where sulfa and sulfites are found and what to avoid if you're sensitive to sulfa or sulfites.

Person using asthma inhaler

Arnav Pratap Singh / Getty Images

Sulfa Allergy

A sulfa allergy is an allergy to drugs with a sulfonamide group as part of their chemical structure. These can be antibiotics, diuretics (water pills), eye drops, topical creams, and other types of drugs.

Sulfa-based antibiotics are commonly used to treat skin, hospital-acquired, and fungal infections. Some researchers estimate that sulfa allergies impact up to 8% of people who use these drugs worldwide.

Symptoms of a Sulfa Reaction

Sulfa allergies can present in a multitude of ways, including as a rash. Your reaction may range from mild to severe.

No matter how your allergies present, you should consult a healthcare provider immediately. An initially mild allergic reaction can quickly progress to anaphylaxis, a severe life-threatening reaction requiring emergency medical care.

A generalized flat, red rash, also known as maculopapular eruption, is the most common symptom of a sulfa allergy, but you may also experience the following symptoms:

  • Generalized itching (pruritus)
  • Hives (urticaria), in which the red, itchy rash develops into raised welts with a clearly defined border
  • Swelling of the face, lips, hands, or tongue (angioedema)
  • Shortness of breath, which in severe cases may be a sign of anaphylaxis
  • Stevens-Johnson syndrome or toxic epidermal necrolysis, which is a blistering rash that destroys the top layers of your skin and mucous membranes

Sun exposure can trigger or worsen your rash. Finding some shade and cooling your body down with ice are some initial steps you can take should you develop a mild skin rash. 

List of Drugs That Contain Sulfa

In some people, sulfa drugs can cause the body to release histamine, causing a systemic (body-wide) inflammatory response that can affect one or more organs.

If you have a sulfa allergy, you should avoid antibiotics such as Bactrim or Septra (TMP/SMX, trimethoprim-sulfamethoxazole). Trimethoprim-sulfamethoxazole is the most commonly used sulfa antibiotic. Because sulfamethoxazole is often combined with trimethoprim, any antibiotic with trimethoprim should be avoided.

Other sulfa antibiotics include sulfadiazine, Silvadene (silver sulfadiazine), AVC Vaginal (sulfanilamide), and sulfacetamide (found in over-the-counter and prescription topical products).

Sulfonamide-containing nonantimicrobial agents include several classes of drugs. Some healthcare providers will avoid prescribing these to people with an allergy to sulfonamide-containing antimicrobials. However, research has shown that a reaction is unlikely, so they might be prescribed. These drugs include.

Sulfite Allergy

A negative reaction to sulfites may cause a true allergy (in which the immune system reacts to their presence) or a sensitivity (in which symptoms are displayed but there isn't an immune system reaction).

Symptoms of a Sulfite Reaction

A true sulfite allergy usually leads to asthma-like symptoms. Sulfite sensitivity may cause gastrointestinal symptoms. You may experience the following symptoms if you have an immune reaction to sulfite:

If you ingest sulfite in processed food or white wine, you may experience gastrointestinal symptoms such as bloating, diarrhea, indigestion, and vomiting, which is indicative of sulfite sensitivity, especially if there are no upper respiratory symptoms. 

Foods and Beverages With Sulfites

If you are a wine or beer drinker, chances are you've ingested some sulfites in your lifetime, as they are naturally present in fermented foods. Many foods contain sulfites, especially processed foods, to prevent spoilage.

Common foods that contain sulfites include:

  • Dried fruits
  • Mushrooms
  • Condiments such as ketchup, mustard, and mayonnaise
  • Frozen shrimp
  • Potato chips
  • Bottled lemon or lime juice
  • Sauerkraut
  • Imported fruit juice and soft drinks
  • Frozen pizza and pie dough
  • Canned and frozen fruits and vegetables

Of note, all the aforementioned foods should be avoided if you have an allergy, but white wine and dried fruits especially should be avoided since they contain the most sulfites.

The Food and Drug Administration (FDA) requires sulfites to be listed on food labels if the food contains more than 10 parts per million (ppm). Examples of sulfites include:

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

Sulfa vs. Sulfites

Sulfites are commonly added to foods to preserve them and are naturally present in fermented foods. If you are sensitive to or allergic to sulfites, check food labels and ask restaurant staff about the ingredients in the food. The FDA banned sulfites on fresh fruits and vegetables in 1986.

Notably, sulfite is added to medications such as epinephrine, Thorazine (chlorpromazine), and dopamine to prevent discoloration. However, an epinephrine injection (such as an EpiPen) should be administered even to a person with a sulfite allergy if they are experiencing anaphylaxis, as it is needed to save their life.

Sulfa is mostly contained in medications and supplements. There is no test for a sulfa allergy, so people usually find out that they have an allergy after an adverse medical reaction to a drug, supplement, or personal care product. 

Reactions to sulfa drugs and sulfite develop within one to 48 hours of ingesting the substance. Both typically resolve within two weeks of stopping the offending agent. Discontinuation soon after the appearance of an itchy rash or hives may lead to a resolution of your symptoms. Antihistamines and corticosteroids may help.

No treatment prevents sulfite reactions, so you must avoid the triggering substances. Some healthcare providers may try a desensitization program for an allergy to sulfa drugs, prescribing small but increasing doses to improve tolerance.

Be sure to report any known or suspected allergies to a healthcare provider so they can avoid prescribing medications that might trigger a reaction.

Summary 

Sulfa drug and sulfite allergies sound similar in name but are two distinctly different things. Sulfites are commonly found in packaged foods and wines, whereas sulfa is found in medicines (particularly antibiotics) and supplements.

Sulfite allergies usually present with asthma-like symptoms such as wheezing and trouble breathing, whereas sulfa allergies typically present with a rash. See a healthcare provider if you have a reaction. Seek emergency medical care for a severe reaction.

Knowing what triggers the allergy or sensitivity and avoiding it is key to preventing further reactions. Report any allergies to your healthcare provider. Check food labels if you have a reaction to sulfites.

A Word From Verywell

Sulfites are preservatives that may seem impossible to avoid if you have a sulfite allergy or sensitivity. This can be frustrating, but eating fresh fruits and vegetables limits your sulfite intake to a negligible amount. 

Sulfa allergies are usually experienced early after taking medications. Always inform a healthcare provider of a known sulfa allergy.

Whether you have a sulfa or sulfite allergy, let your family members and friends know, and explain to them the difference between the two, so they can help you avoid the substances (like medications for sulfa and foods for sulfite allergies) that may cause you to become ill.

Frequently Asked Questions

  • What drugs are safe for someone with sulfa allergy?

    There are many non-sulfa antibiotics that you can take in place of sulfa-containing antimicrobials. For urinary tract infections, these include Cipro (ciprofloxacin). The specific antibiotic that will work best for you will depend on the bacteria in question and your allergy profile.

  • Can you get tested for sulfa allergy?

    No. There are no tests to diagnose a sulfa allergy. The diagnosis is made based on your symptoms, physical examination, and medical history.

  • How do you treat sulfite allergy?

    The best way to avoid a negative immune response from a sulfite is to avoid that substance entirely. Sulfite allergies have no cure.

    In people with asthma who have a sensitivity to sulfites, using an asthma inhaler may help with symptoms affecting breathing. Oral steroids may be needed. For skin reactions, antihistamines and a cortisone cream may help with the rash. For symptoms of anaphylaxis, seek emergency medical care.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. University of Nebraska-Lincoln. Sulfites - USA.

  3. Australian Society of Clinical Immunology and Allergy. Sulfite sensitivity frequently asked questions (FAQ).

  4. Mechtler AG, Chamarro-Pareja N, Carillo-Martin I, Haehn D, Gonzalez-Estrada A. Six-step trimethoprim-sulfamethoxazole desensitization protocol in non-HIV patients with self-reported sulfa allergy: a single center experienceJ Allergy Clin Immunol. 2019:143(2):AB33. doi:10.1016/j.jaci.2018.12.102

  5. American College of Allergy, Asthma, and Immunology. Drug allergies.

  6. New York Allergy and Sinus Center. Sulfite allergy.

By Shamard Charles, MD, MPH
Shamard Charles, MD, MPH is a public health physician and journalist. He has held positions with major news networks like NBC reporting on health policy, public health initiatives, diversity in medicine, and new developments in health care research and medical treatments.