Like other drug allergies, a sulfa allergy may be accompanied with symptoms like hives, itchy skin, or swelling in the mouth or throat. It differs from a sulfite allergy.

A sulfa allergy is when you have an allergic reaction to drugs that contain sulfa. About 3 percent of people prescribed sulfa antibiotics will have an adverse reaction to them, according to one review. However, it’s estimated that of those who have an adverse reaction, only 3 percent are true allergic reactions. That means that number of people who experience an allergic reaction to sulfa is extremely low.

Sulfa vs. sulfite allergy

Sulfa allergies and sulfite allergies aren’t the same thing. Sulfites occur naturally, or are used as a preservative agent in some foods and drinks. Sulfa medications and sulfites found in food and drink aren’t related to each other. The similarity between their names can cause some confusion. Read more about the difference between sulfa allergies and sulfite allergies.

Symptoms of sulfa allergy are similar to those of other drug allergies. Symptoms may include:

  • skin rash or hives
  • itchy eyes
  • itchy skin
  • congestion
  • swelling of the mouth
  • swelling of the throat

Sulfa allergy can result in serious complications, including anaphylaxis and Stevens-Johnson syndrome.


Anaphylaxis is a severe and potentially life-threatening type of allergic reaction. You’re at an increased risk for this type of reaction if you have:

  • other allergies
  • asthma
  • a family history of anaphylaxis

Symptoms of anaphylaxis typically develop within 5 to 30 minutes of exposure to an allergen. These symptoms include:

  • an itchy red rash that includes hives or welts
  • swelling in the throat or possibly other areas of the body
  • wheezing, coughing, or difficulty breathing
  • tightness of the chest
  • difficulty swallowing
  • vomiting
  • diarrhea
  • cramping of the stomach
  • pale or red color of the face or body

Stevens-Johnson syndrome

Stevens-Johnson syndrome is a rarer complication of sulfa allergy. This condition consists of painful and blistered lesions on the skin and mucus membranes, including the:

  • mouth
  • throat
  • eyes
  • genital region

Stevens-Johnson syndrome is more common in men than women. Some people also have a genetic predisposition for the condition.

Symptoms of Stevens-Johnson syndrome include:

  • abnormal skin blistering
  • reddening of the skin
  • fatigue
  • diarrhea
  • nausea and vomiting
  • fever

Sulfa is found in a variety of medications, including antibiotics and nonantibiotic drugs. An allergic reaction is more likely to occur from exposure to sulfa-containing antibiotics.

Sulfa-containing drugs include:

Are sulfas found in foods?

Having an allergy to sulfa drugs is different from having an allergy to food or drinks that contain sulfites. Unless you’ve had a reaction to sulfites, consuming food or drink that contains sulfites is OK. Conversely, if you’ve had an allergic reaction to sulfites, it doesn’t mean that you’ll also be allergic to sulfa drugs.

If you have an allergic reaction to sulfa drugs, treatment will be centered on relieving your symptoms. Your doctor may prescribe antihistamines or corticosteroids to relieve hives, rash, and itching. A bronchodilator may be prescribed if you have respiratory symptoms.

Your doctor may recommend a desensitization procedure if you need medication and there isn’t a sulfa-free alternative. Desensitization involves slowly introducing the medication at low doses until an effective dose is reached and tolerated. You’ll be monitored for allergic reactions as the medication doses are increased.

Both anaphylaxis and Stevens-Johnson syndrome require immediate medical attention. If you’re having an anaphylactic reaction, epinephrine will usually be given.

If you develop Stevens-Johnson syndrome, you’ll likely be admitted to an intensive care unit. Treatment for Stevens-Johnson syndrome includes:

  • corticosteroids to control inflammation
  • antibiotics to prevent or control skin infections
  • intravenous (IV) immunoglobulins to halt the progress of the disease

There are no diagnostic tests for sulfa allergy. However, some tips for prevention of a further allergic reaction to sulfa drugs include:

  • Make sure all healthcare providers, including your dentist and pharmacy, are aware of your drug allergies. This will help them be aware of which medications should be avoided.
  • If you have previously had a severe or anaphylactic reaction to sulfa drugs, carry an emergency epinephrine syringe (EpiPen).
  • Carry a medical alert card with you or wear a medical alert bracelet that alerts care staff of your allergy. This will ensure proper treatment if you have a reaction and are unable to verbally alert medical providers of your allergy.

Having a sulfa allergy means you have an allergic reaction to medications containing sulfa. While there are many medications that contain sulfa, allergic reactions to sulfa antibiotics are most common. Sulfa allergy and allergy to sulfites found in food or drink aren’t the same thing.

Symptoms of an allergic reaction to sulfa drugs include rash or hives, itchy skin or eyes, and swelling. Complications of sulfa allergy include anaphylaxis and Steven-Johnson syndrome. Both of these are considered medical emergencies.

Always make sure that your healthcare providers are aware of your sulfa allergy so medications containing sulfa can be avoided. Let your healthcare provider know right away if you suspect a sulfa allergy.