Onions are a common ingredient in cuisines worldwide because of their versatility and flavor. However, for some people, eating onions can lead to uncomfortable or even dangerous reactions.

Can You Be Allergic to Onions?

While uncommon, it’s possible to have an onion allergy. Onions belong to the allium family, which also includes garlic, chives, leeks, and shallots. An allergy to onions often extends to other members of the allium family due to their similar protein structures.

There are three primary allergens in onions. The most common allergen is called alliin lyase. Cutting onions also releases sulfurous substances that can cause reactions like watery eyes, nasal congestion, or allergic reactions on the skin.

Many people who have reactions to onions may actually have an intolerance rather than a true onion allergy.

Can You Be Allergic to Red Onions but Not White Onions?

There isn’t specific research about being allergic to only one type of onion. However, people have reported being allergic to only one type of onion on online health forums.

It's important to note that while they are different colors, red and white onions share very similar protein structures. The primary difference between them is their color.

Compounds Within Onions

Some people might be sensitive to specific compounds that are found more in red onions. For instance, red onions generally contain higher levels of quercetin, a flavonoid with antioxidant properties, than white onions. It’s possible that some people might have a sensitivity to it and experience side effects like upset stomach or headaches.

Raw vs. Cooked Onions

Another factor to consider is the difference between raw and cooked onions. Some people report being able to tolerate cooked onions but not raw ones. This could be due to how cooking changes proteins and other compounds in food.

It’s possible that some people mistakenly attribute their reaction to the color of the onion when it’s actually related to whether the onion is raw or cooked. Some MyFoodAllergyTeam members mentioned that they have noticed less severe symptoms when eating cooked or fried onions.

If you’ve noticed that you have reactions to one type of onion, talk to your primary care provider or an allergist for guidance.

Onion Allergy vs. Onion Intolerance

Having a negative reaction to eating onions doesn’t necessarily mean you have a food allergy. You might have a food intolerance, also called a food sensitivity. While both allergies and intolerances can cause discomfort, they have different causes and treatments.

An onion allergy is an immune system response. When someone who is allergic to onions eats one, their immune system confuses the onion as a harmful substance. Their immune system then produces antibodies, histamine, and other chemicals to fight it off. As a result, people can experience allergy symptoms such as trouble breathing or itchiness. With a true onion allergy, people are more likely to react to all onion types, not just red onions.

On the other hand, an onion intolerance, or onion sensitivity, is a nonimmune reaction. It can inhibit the body’s ability to digest certain foods properly. Intolerances tend to be more common and less severe for individuals than allergies. Common symptoms include cramping, bloating, and rashes.

How Common Are Onion Allergies and Intolerances?

True onion allergies are rare. The exact prevalence is difficult to determine since it’s relatively underreported.

One study in 2020 found that out of 8,109 people, roughly 11 percent were hypersensitive to food. Less than 1 percent, or 10 people, were sensitive to onions.

Another study from 2013 aimed to measure the allergy potential for garlic and onions. In 108 people, only 15 had a reaction to garlic and onions. Only one person had an onion-only allergy.

Symptoms of Onion Allergies

The symptoms of an onion allergy can range from mild to severe. They typically appear within minutes to two hours after exposure to onions. Common symptoms include:

• Skin reactions (hives, itching, rashes, or contact dermatitis)
• Tingling or itching in the mouth
• Swelling, particularly of the face, lips, tongue, or throat
• Difficulty breathing, nasal congestion, or asthmalike symptoms
• Itchy or watery eyes
• Nausea, vomiting, stomach cramps, diarrhea, or gas

In most cases, allergy symptoms resolve fully once the onions have left the digestive system.

In rare cases, an onion allergy can lead to anaphylaxis. This is a severe and potentially life-threatening allergic reaction that requires immediate medical attention. People who have an anaphylactic reaction to onions should carry an epinephrine auto-injector.

Diagnosis of Onion Allergies

Diagnosing an onion allergy typically involves several steps. Your doctor or allergist will often begin with a detailed discussion of your medical history, including your symptoms, their timing, and potential triggers.

Elimination Diet

Your doctor may recommend an elimination diet, in which you avoid eating onions for a period of time. They may have you gradually reintroduce onions over time and note any reactions in a food diary. If your symptoms flare when consuming onions, they are most likely caused by the onions themselves.

Food Allergy Testing

Your doctor may want to confirm your allergy with food allergy testing. If approved by your doctor, you could also experiment with different preparation methods. Some people have found that they can tolerate small amounts of cooked onions but not raw ones.

Skin Prick Test

Skin prick tests also can test for onion allergies, with results usually in about 15 minutes to 20 minutes. In a skin prick test, a health care professional applies the suspected allergen to your skin, usually on your arm or back, using a sterile needle or probe. If your skin becomes raised and itchy, like a mosquito bite, you may have an allergy.

Blood Test

A blood test can measure the levels of specific immunoglobulin E (IgE) antibodies to onion proteins. You can typically expect results back within a few days.

Oral Food Challenge

Another possible diagnosis method is an oral food challenge. Under medical supervision, you eat increasing amounts of onions at your allergist’s office so they can observe any allergic reactions. Your allergist can administer medical treatment if necessary. Don’t try an oral food challenge at home without proper medical supervision.

Treatment and Management of Onion Allergies

The primary management strategy for both onion allergy and intolerance is avoidance. This involves carefully reading food labels and being cautious when eating out. Onions and onion powder are common ingredients in many dishes and processed foods.

Research Menu Ingredients Before Eating Out

When it comes to eating out, one MyFoodAllergyTeam member recommends researching common ingredients in dishes beforehand. They added, “It isn’t always enough to avoid a reaction, but it helps me to stay away from general dishes that will never, and can never, be safe, no matter how much I want it.”

Check for Cross-Contamination Potential

Many MyFoodAllergyTeam members also warn about cross-contamination. A few members have shared experiences where onions have been cut on the same surfaces or slicers as their food, causing adverse reactions.

Read Ingredient Lists Carefully

The U.S. Food and Drug Administration (FDA) does not require onions to be listed as an allergen on food labels, so carefully examine ingredient lists. It’s common to find traces of onions and other alliums in salsas, broths, flavoring packets, and premade sauces and soups.

Use Allergy Treatments if You’re Exposed

If you eat onions and get a rash, use hydrocortisone cream or aloe vera for relief from the itching and inflammation. Your doctor may also recommend antihistamines to reduce allergy symptoms. Sometimes inhalers can help with breathing.

Carry an Epinephrine Auto-Injector

If you have a true onion allergy, always carry an epinephrine auto-injector for emergency treatment of severe reactions. These can be prescribed by your doctor.

Find Substitutes

With both onion allergies and intolerances, it’s important to find substitutes to maintain a balanced diet, especially when cooking. You can try replacing onions with vegetables like celery, carrots, or fennel and even try herbs such as thyme, sage, or tarragon.

Consult With Your Health Care Provider

If you’re concerned about an onion allergy or intolerance, talk to your doctor. If you don’t already have an allergist, they may refer you to one for allergy testing and guidance for developing an allergy treatment plan.

Talk With Others Who Understand

MyFoodAllergyTeam is the social network for people with food allergies and their loved ones. On MyFoodAllergyTeam, more than 41,000 members come together to ask questions, give advice, and share their stories with others who understand life with food allergies.

Do you have an onion allergy or intolerance? Have you found good onion substitutes? Share your experience in the comments below, or start a conversation by posting on your Activities page.