Sulfa Allergy

A sulfa allergy is an allergic reaction to drugs containing sulfonamides. The most common reaction is a skin rash or hives, but more serious reactions like breathing issues can also happen. Avoiding medications containing sulfa is the best prevention.


What is a sulfa allergy?

A sulfa allergy is a type of medication allergy. If you have a sulfa allergy, taking medications containing sulfa can cause an allergic reaction. The most common symptom of a sulfa allergy is a skin rash and hives, although some people have more severe symptoms, like swelling of their throat or shortness of breath. Contact your healthcare provider if you experience any adverse reactions to medication. Seek emergency care if your symptoms progress or include difficulty breathing.

“Sulfa” is short for sulfonamides, a class of drugs that consists mostly of antibiotics. It’s also contained in other medications. Antibiotics are medications you take for bacterial infections. Sulfa drugs work by preventing bacteria from producing a substance they need to grow and multiply. Sulfonamides can be taken orally (by mouth) or applied directly to your skin or eyes (topical).

Once you know you have an allergy to sulfa, avoiding medications containing sulfa is the best treatment. You should always let your healthcare providers know about any drug allergies you have so they can put a note in your medical history.


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What are the most common sulfa drugs?

Sulfa is an ingredient in some antibiotics that treat the following conditions:

The most common sulfonamides are:

  • Mafenide.
  • Sulfacetamide.
  • Sulfadiazine.
  • Sulfadoxine.
  • Sulfamethizole.
  • Sulfanilamide.
  • Sulfasalazine.
  • Sulfisoxazole.
  • Sulfamethoxazole/trimethoprim.
  • Dapsone.

The most common allergic reaction is to sulfamethoxazole/trimethoprim (Bactrim™, Sulfatrim™).

Other medications that contain sulfa

Some nonantibiotic medications that may contain sulfonamide are:

How common is a sulfa allergy?

About 6% of people who use medications containing sulfa react to them.

Symptoms and Causes

What are the signs of a sulfa allergy?

People with an allergy to sulfa drugs may have the following symptoms:

  • Itchy skin.
  • Skin rash.
  • Hives.
  • Sensitivity to sunlight. This means your rash worsens with exposure to the sun.
  • Swelling in your hands, feet, mouth and tongue.
  • Nausea, vomiting or diarrhea.
  • Headache.

Some less common, but potentially serious symptoms of sulfa allergies are:

  • Difficulty swallowing.
  • Breathing trouble.
  • Muscle and joint aches.
  • Sore throat.
  • Fever and flu-like symptoms.
  • Skin blisters and peeling skin.

Some people develop anaphylaxis, a rare but serious allergic reaction that can lead to coma, organ failure or even death. Other serious, but rare complications from a sulfa allergy include Stevens-Johnson syndrome and toxic epidermal necrolysis (TEN). These conditions cause your skin, mouth or genitals to develop rashes and blisters, and then peel.

Who is at risk for a sulfa allergy?

Studies show that people with HIV/AIDS may be at increased risk of allergies to sulfa medications. People who have a weaker immune system may also be at higher risk. Sulfa drugs can trigger hemolytic anemia in those with G6PD (glucose-6-phosphate dehydrogenase) deficiency.


Diagnosis and Tests

How do I know if I have a sulfa allergy?

Healthcare providers don’t typically use tests to diagnose a sulfa allergy. Instead, your healthcare provider will ask you questions about your medication use and review your symptoms to see if a sulfa allergy is the cause of your allergic reaction.

It’s possible to test for sulfa sensitivity by taking sulfa medication under medical supervision to see if it triggers a reaction. This is called an oral drug challenge test. But many providers don’t want to take the chance because this might trigger a severe reaction.

If your provider finds that you have a sulfa allergy, they may need to find an alternative medication to treat your condition. If you have to take a sulfa medication, your healthcare provider may recommend desensitization therapy. This is a way to gradually build your tolerance for a medication to reduce the severity of your reaction. While it allows you to take sulfa for a short time, it doesn’t cure you or make you not allergic.

Management and Treatment

How is a sulfa allergy treated?

Avoiding medications containing sulfa is the best treatment. As you won’t learn you have a drug allergy until after you’ve taken it, it’s impossible to know ahead of time how your body will react to a medication.

For mild allergic reactions, your healthcare provider may recommend taking antihistamines or corticosteroids until symptoms subside. More severe reactions may require an epinephrine injection (EpiPen®).

While most people have mild to moderate reactions to a sulfa allergy, some people can experience life-threatening symptoms like difficulty breathing and painful blisters on their skin, mouth or genitals. These symptoms require immediate attention in an emergency room.

Are there other drugs I should avoid?

Let your healthcare provider know if you experience a reaction to sulfonamides or any other medications. There may be other drugs they want you to avoid taking.



Can you prevent a drug allergy?

No, there isn’t a way to prevent a drug allergy. You can only avoid the drug in the future. Your healthcare provider and pharmacy should be aware of any drug allergies you have. Some people wear a medical bracelet or carry a card in their wallet or on their phone that states they have a sulfa allergy. This can be helpful in the event you experience an emergency and can’t communicate.

Living With

When should I see my healthcare provider?

Always let your healthcare provider know about allergic reactions or side effects you experience after taking a medication. This helps them recommend the best medication for you moving forward. It also ensures they don’t prescribe medication that can potentially cause an allergic reaction.

Additional Common Questions

Is amoxicillin a sulfa drug?

No, amoxicillin isn’t a sulfa drug. It’s a type of penicillin. Penicillin allergies are common.

Is prednisone a sulfa drug?

No, prednisone is in a class of drugs called corticosteroids.

Are sulfites the same as sulfa?

Sulfa allergies and sulfite allergies aren’t the same. Sulfites occur mainly in food products as a preservative to slow discoloration. While the names sound similar, there isn’t a link between the two allergies.

A note from Cleveland Clinic

A sulfa allergy occurs when you have an allergic reaction to sulfonamides, which are in drugs to treat bacterial infections. The most common symptoms of a sulfa allergy are hives, skin rash, itchy skin and sensitivity to sunlight. If you experience any of these symptoms after taking medication for an infection, let your healthcare provider know. There should be alternative antibiotics you can take that won’t give you symptoms. While it may be scary to have an allergy to medication, telling all of your healthcare providers about it is the best way to protect yourself from another allergic reaction.

Medically Reviewed

Last reviewed on 07/14/2023.

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