Sulfa Allergy

Medically Reviewed by Carol DerSarkissian, MD on November 02, 2022
4 min read

A sulfa allergy is a rash or more serious reaction to sulfa drugs. These drugs can treat a range of health problems from eye infections to rheumatoid arthritis (RA). 

Sulfa drugs, also called sulfonamides, include antibiotics as well as other types of drugs. Allergies happen most often with antibiotics. About 3 percent of people have some type of reaction to them.

Tell your doctor right away if you think you’re having a reaction to a sulfa drug. They’ll decide whether to take you off the drug and how to treat your symptoms.

If you’re allergic to sulfa drugs or any other medication, you may have one or more of these symptoms:

The reaction can also cause these serious skin reactions:

  • Sulfonamide drug hypersensitivity syndrome. Rash, fever, and organ problems begin a week or two after you start the drug.

  • Drug eruption.Red or swollen, rounded patches form in 30 minutes to 8 hours.

  • Stevens-Johnson syndrome. This potentially life-threatening reaction causes skin to blister and peel off.

Other reactions to sulfa drugs include headache, trouble sleeping, cloudy urine (crystalluria), and low blood counts. Rarely, a severe allergic reaction called anaphylaxis happens.

Sulfa antibiotics have been widely used for more than 70 years. The first antibiotic was a sulfa drug introduced in 1936. Today, these drugs include burn creams, vaginal suppositories, and eye drops as well as medications for many types of infections. If you’ve had an allergic reaction to one sulfa antibiotic, you’re probably allergic to all of them.

Here are a few examples of common sulfa drugs that could cause problems:

Some sulfa drugs may be OK

Even if you’re allergic to antibiotics that have sulfa, you might be able to take some other types of sulfa drugs without a reaction. Ones that may be safe to take include:

But be sure to tell your doctor if you have a sulfa allergy before taking any of these.

You and your doctor will want to treat your allergy symptoms right away. Medications for a sulfa allergy in

  • Antihistamines

  • Corticosteroids

  • Epinephrine (for anaphylaxis)

If you’re allergic to a medication that you need to take, your doctor could start it slowly. This is called drug desensitization. You’ll take a very small dose at first and then larger doses over several hours or days. Your doctor will watch you closely for any negative reactions.

Though rare, a sulfa allergy can cause serious problems, such as: 

  • Anaphylaxis. This life-threatening reaction to a drug allergy causes trouble breathing, a drop in blood pressure, and other symptoms.

  • Stevens-Johnson syndrome. This is a disorder of the skin and mucous membranes that starts with flu-like symptoms followed by a painful rash.

If you have a drug allergy, it’s best to avoid medications that will cause a bad reaction or side effect. Here are some other tips:

  • Notify your health care providers. Tell them about any drug allergies so they can make a note in your medical records.

  • Wear a medical bracelet. In an emergency, a bracelet will alert health care providers about any drug allergies.

A sulfa allergy sounds like a sulfite allergy, but they’re very different. Sulfa drugs treat health conditions. Sulfites are preservatives used in many foods, drinks (especially wine), and medications.

Sulfites can trigger asthma symptoms and, on rare occasions, can cause anaphylaxis. It’s common for people who have asthma to be sensitive to sulfites. But it’s unusual for other people.

Sulfa drugs and sulfites are not related. Neither are their allergies. There’s no need to give up dried fruit, wine, or other items that have sulfites if you’re sensitive to sulfa drugs.