Sulfa Allergy Symptoms and Risks

In This Article

Sulfa allergy is a term used to describe an adverse drug reaction to sulfonamides, a class of drugs that includes both antibiotics and non-antibiotics.

Ideally, a physician will document what specific sulfa drug was associated with what specific reaction as the term "sulfa allergy" alone may unnecessarily lead to avoidance of drugs that may be tolerated.

There's a common misconception that all sulfonamide drugs are equally likely to cause an allergic or adverse reaction, but this isn't true. (All drugs have the potential to cause allergy.) Antibiotic sulfonamides (used to treat bacterial infections) are more likely to trigger an allergic reaction than nonantibiotic ones.

While all drugs have the potential to cause an allergy, non-antibiotic sulfonamides are less likely sources.


In the majority of cases, a person with a sulfa allergy will have experienced an allergic reaction to one or more of the following antibiotic drugs:

  • Septra (sulfamethoxazole and trimethoprim)
  • Bactrim (sulfamethoxazole and trimethoprim)
  • Pediazole (erythromycin and sulfafurazole)

These reactions are not all that uncommon and affect around 3 percent of all people. This is a rate similar to what is seen with other types of antibiotics, including penicillin.

Certain people appear to be at higher risk of sulfa allergy than others. These include those who, for various reasons, have a suppressed immune system (such as organ transplant recipients and people with HIV/AIDS).


Common symptoms of a sulfa allergy
Illustration by Brianna Gilmartin, Verywell

The symptoms and severity of a sulfa allergy can vary but usually involve the appearance of a widespread rash. Occasionally a photosensitive rash may develop, meaning that a rash will occur in areas exposed to sunlight or other UV light while on the medication.

In more severe cases, the outbreak of rash may be accompanied by the swelling of the face, hands, feet, and tongue (known as angioedema). Blistering of the skin is concerrning for potentially life-threatening reactions such as Stevens-Johnson syndrome and toxic epidermal necrolysis.

Other serious manifestations of a sulfa allergy include:

It's important to take every drug-related rash seriously, no matter how mild it may be. In some cases, continuing a sulfa-drug while having mild symptoms may cause those mild symptoms to become severe and life-threatening.


There's no validated skin or blood test available to diagnose a sulfa allergy. The diagnosis is usually made on careful review of the suspected reaction and history of current and previous medication use.


The first-line of treatment of a sulfa allergy is typically the termination of the suspected drug.

Anaphylaxis requires immediate epinephrine use and medical care.

Stevens-Johnson syndrome or toxic epidermal necrolysis are also potentially life-threatening conditions that require immediate medical evaluation; in severe cases, management in a burn unit may be required.

In milder cases where a sulfa drug is considered essential to the treatment of an infection, an allergist or other qualified physician may supervise the administration of smaller doses and gradually increase them as the drug is better tolerated.

Medications to Avoid

People with a known sulfa allergy should always check with their doctor before starting a new medication. This is especially true for those who have had a previous severe reaction.

In addition to oral antibiotics, topical sulfonamides should be avoided. These include:

  • Sulfacetamide eye drops, shampoos, or creams
  • Silver sulfadiazine ointments used to treat burns
  • Sulfanilamide vaginal preparations

Similarly, the oral drug Azulfidine (sulfasalazine), used to treat inflammatory bowel disease and rheumatoid arthritis, should be avoided.

Keep in mind that the risk of cross-reactivity to non-antibiotic sulfonamides is low. This means that it's generally safe to take the following drugs:

  • Diuretics (water pills) such as HCTZ (hydrochlorothiazide) and Lasix (furosemide)
  • Oral sulfonylureas-class drugs used to treat diabetes
  • Celebrex (celecoxib), a COX-2 inhibitor used to treat arthritis and pain

Sulfite and Sulfate Allergies

People will often mistake a sulfa allergy for a sulfite allergy. Sulfites are preservatives found in foods and medications. These include:

  • Sodium sulfite
  • Sodium bisulfite
  • Sodium metabisulfite
  • Potassium bisulfite
  • Potassium metabisulfite

While sulfites can cause an ​allergy, there is no direct relationship between a sulfa and sulfite allergy—so someone with a sulfa allergy doesn't have to avoid sulfites (or vice versa).

Sulfates are drugs containing sulfuric acid. As with sulfites, sulfates may cause allergy, but the drugs are in no way related to sulfonamides or sulfa-allergy risk. These include medications such as:

  • Albuterol sulfate used to treat bronchial spasms
  • Iron sulfate used to treat iron-deficiency anemia
  • Chondroitin sulfate used to treat osteoarthritis
  • Codeine sulfate, an opioid drug used for pain relief

A Word From Verywell

The nuances of a sulfa allergy can be tricky to tease out, even for some healthcare providers. That's why it's important to tell your doctor about any prior reaction you may have had to a sulfa medication (or any other drug for that matter). Sharing that information will make it easier for your doctor to prescribe a substitute that's less likely to cause an allergy.

Was this page helpful?

Article Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial policy to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Zawodniak, A.; Lochmatter, P.; Beeler, A. et al. Cross-reactivity in drug hypersensitivity reactions to sulfasalazine and sulfamethoxazole. Int Arch Allergy Immunol. 2010;153(2):152-6. doi:10.1159/000312632

  2. Platt D, Griggs RC. Use of acetazolamide in sulfonamide-allergic patients with neurologic channelopathies. Arch Neurol. 2012;69(4):527-9. doi:10.1001/archneurol.2011.2723

  3. Wulf, N. and Matuszewski, K. Sulfonamide cross-reactivity: is there evidence to support broad cross-allergenicity? Am J Health Syst Pharm. 2013 Sep 1;70(17):1483-94. doi:10.2146/ajhp120291

  4. Meyer C, Behm N, Brown E, Copeland NK, Sklar MJ. An Adverse Drug Reaction to Trimethoprim-Sulfamethoxazole Revealing Primary HIV: A Case Report and Literature Review. Case Rep Infect Dis. 2015;2015:691010. doi:10.1155/2015/691010

  5. Schnyder B, Pichler WJ. Allergy to sulfonamides. J Allergy Clin Immunol. 2013;131(1):256-7.e1-5. doi:10.1016/j.jaci.2012.10.003

  6. Harr T, French LE. Toxic epidermal necrolysis and Stevens-Johnson syndrome. Orphanet J Rare Dis. 2010;5:39. doi:10.1186/1750-1172-5-39

Additional Reading