Contrast Dye Allergy: Symptoms and What to Do

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A contrast dye reaction can occur after a diagnostic imaging test, such as an MRI or CT scan. Contrast dye is an iodine-based or gadolinium-based substance that's given through a vein to help internal structures stand out during scans. Studies show that less than 1% of people who receive contrast dye will have a serious allergic reaction.

Most reactions occur within an hour of receiving contrast dye and many occur within the first five minutes. However, there can sometimes be delayed reactions that occur up to a week later. Symptoms can include serious allergic-like symptoms, such as skin reactions or trouble breathing.

This article will further explore the symptoms of a contrast dye allergic reaction, risk factors for reactions, and how a contrast dye allergy is treated.

Iodinated contrast dye is used for scans involving X-rays, such as CT scans. Gadolinium-based contrast is used for MRIs. The likelihood of a reaction to LOCM iodine-based dye is much lower than that with HOCM iodine-based dye, and the likelihood of a reaction to a gadolinium-based contrast is even lower.

Doctor looking at image from coronary angiography
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Symptoms of Contrast Dye Allergy

Contrast dye acts to directly release chemicals, such as histamine. This triggers allergic-like symptoms. A true allergy occurs due to the production of antibodies, which are specialized immune proteins. This typically does not happen with contrast dye reactions, but it has been described.

The severity of a contrast dye reaction can range from mild to severe and life-threatening. Mild reactions are relatively common, occurring in 3% to 15% of people receiving contrast. Most of these reactions include:

  • A feeling of warmth
  • Nausea
  • Vomiting

Generally, symptoms of a mild reaction occur for a short period and don't require treatment. Severe reactions occur in less than 1% of people receiving contrast. Symptoms of a moderate or severe reaction that require urgent medical care include:

  • Severe vomiting
  • Hives
  • Difficulty breathing
  • Swelling in the throat
  • High-pitched sound when breathing
  • Convulsions
  • Fast heart rate
  • Loss of consciousness

Some of these symptoms may occur if the allergic reaction causes cardiac arrest.

Risk Factors

These factors appear to put people at higher risk for adverse or allergic reactions to contrast dye:

  • Past reactions to a similar type of contrast
  • Having asthma
  • Having allergies
  • Having heart disease
  • Having kidney disease
  • Taking beta-blockers, which are medications commonly used for a variety of conditions, including heart conditions

Older adults also have an increased risk for severe reactions.

The Seafood Myth

Despite the popular myth, having a seafood allergy does not place you at an increased risk of having a reaction to contrast dye. Shellfish allergy is due to the protein content of these foods, not the iodine content.

In addition, if you have an allergy to topical iodine cleaners or iodides, you're at no increased risk for these reactions.


The treatment is symptomatic, meaning that treatment is given to alleviate the specific effects of the reaction.

Treatment may include the following:


Unfortunately, there is no test available to diagnose a contrast dye allergy in advance. Skin testing and blood testing to look for allergies are often not helpful in the diagnosis.

Reactions are unpredictable and small test doses do not indicate whether or not a reaction will occur when a regular amount is given. There are even reports of severe, life-threatening reactions to contrast dye occurring after a person had tolerated a small test dose of IV dye.

There are steps you can take, however, if you've had a non-severe reaction to contrast dye in the past and need to use a similar type for more imaging. In this instance, your medical provider will likely recommend pre-medication. This involves taking medication in advance of receiving contrast dye to lower the risk of a reaction.

It is common to be treated with a pre-medication combination of oral corticosteroids, such as prednisone, and antihistamines, such as Benadryl (diphenhydramine).

If you've had a history of severe reactions, your healthcare provider will avoid using the same class of contrast dye except in specific circumstances. Typically, the reaction is agent-specific and you might be able to use another iodinated contrast from a different class that is low in osmolarity and ionicity if needed.

An IV-dye allergy can only be diagnosed after symptoms have occurred. Otherwise, it's only possible to determine that a person is at increased risk of a reaction.


IV contrast dye is a solution that's put into the bloodstream during medical imaging in order to make internal structures, such as organs and blood vessels, easier to see.

Mild reactions to contrast dye are fairly common and don't require treatment. In rare cases, severe and life-threatening emergencies can occur.

If you're concerned about a potential reaction to contrast dye, talk to your healthcare provider about the risks and benefits of having a test with contrast and whether alternatives are available. If you have a history of reactions to contrast dye, always make your healthcare provider aware of any previous reactions.

Frequently Asked Questions

  • Are IV contrast dyes safe for people who have kidney disease?

    These are generally considered safe, but there is a risk of nephrogenic systemic fibrosis, a rare disease that mostly affects the skin, and contrast-induced nephropathy, which causes a loss of kidney function. These complications are most common among people with existing kidney disease.

  • How common are contrast dye reactions?

    Mild reactions to contrast dye are somewhat common and severe reactions and side effects are rare. If you have a history of allergies, you may need to take medication before receiving the contrast dye to prevent having a serious allergic reaction.

  • Does having contrast dye injected into you hurt?

    No. There may be some discomfort when the IV line is inserted, but you shouldn’t feel pain when the dye is injected. You may have some sensations, though.

    These include:

    • Warm, flushed feeling through your body for a few seconds
    • Metallic taste in your mouth
    • Itchiness
    • Feeling like you're urinating, but you’re not
  • Can I have a contrast dye scan if I have food allergies?

    Any history of allergy increases your risk of having a reaction to contrast agents. However, your healthcare provider may be able to provide medication that you can take before a scan to help prevent a reaction. While there's a myth that shellfish and seafood allergies could put you at particular risk for a reaction to iodine contrast, this is not true.

10 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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Additional Reading

By Daniel More, MD
Daniel More, MD, is a board-certified allergist and clinical immunologist. He is an assistant clinical professor at the University of California, San Francisco School of Medicine and currently practices at Central Coast Allergy and Asthma in Salinas, California.