Decoding Onion Allergy: Symptoms, Diagnosis, and Treatment

Wyndly Care Team
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What are the symptoms of onion intolerance?

Onion intolerance symptoms can manifest as nausea, vomiting, gas, bloating, and heartburn. In some cases, it may lead to diarrhea, stomach pain, and symptoms similar to food poisoning. Severe reactions may also include skin rash or respiratory issues, particularly in asthmatic individuals.

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What Is an Onion Allergy?

An onion allergy is an adverse reaction by the body's immune system to onions. This reaction can range from mild to severe, with symptoms appearing immediately after exposure or with a delay. The allergy can cause various symptoms, including those associated with oral allergy syndrome (OAS) or an allergic reaction.

In some cases, individuals may experience a severe reaction called anaphylaxis, which is a medical emergency. Symptoms of anaphylaxis include difficulty breathing, rapid heart rate, and loss of consciousness. It's essential to seek immediate medical attention if you experience these anaphylaxis symptoms.

It's important to note that onion allergy is different from onion sensitivity or intolerance. With an allergy, the immune system is involved, and reactions can be severe and potentially life-threatening. Whereas, an intolerance involves digestive issues and is typically less severe.

What Are the Symptoms of an Onion Allergy?

Onion allergy symptoms can range from mild to severe, and they typically appear soon after consuming or coming into contact with onions. These symptoms resemble those seen in other food allergies and can affect the skin, respiratory system, and digestive system.

Skin Symptoms

Onion allergic reactions often manifest on the skin. Symptoms include hives, itching, and redness. These skin reactions are similar to what you might see with a pollen allergy, but they occur after consuming or touching onions.

Respiratory Symptoms

In some cases, people with an onion allergy might experience respiratory symptoms. These can include sneezing, runny nose, and itchy or watery eyes, much like ragweed allergy symptoms. In severe cases, there might be wheezing or difficulty breathing, which is a sign of anaphylaxis and needs immediate medical attention.

Digestive Symptoms

Digestive symptoms of an onion allergy can include nausea, vomiting, diarrhea, and stomach pain. These symptoms are often uncomfortable and can be mistaken for a food intolerance rather than an allergy. If you experience these symptoms after eating onions, it's essential to seek medical advice to determine the cause.

How Does an Allergy Differ from a Sensitivity?

An allergy is an immune response to a substance that the body mistakenly identifies as harmful, while a sensitivity or intolerance does not involve the immune system. The primary difference lies in the body's reaction mechanism and the severity of the symptoms.

Allergic Reaction

When you have an allergy, your immune system mistakenly identifies a normally harmless substance as an invader. This substance is called an allergen and can be anything from pollen, like the English plantain, to certain foods, like onions. The immune response can cause symptoms ranging from mild (itching, hives) to severe, like anaphylaxis, which is a potentially life-threatening reaction.

Sensitivity or Intolerance

A sensitivity or intolerance, on the other hand, typically involves less severe symptoms that are often limited to digestive issues. These reactions can occur due to the lack of certain enzymes needed to digest food properly, like lactose intolerance, or a reaction to food additives. Sensitivities can cause discomfort but are not life-threatening like some allergies can be.

Understanding the difference between an allergy and sensitivity is crucial for proper management and treatment. If you're unsure whether your symptoms are due to an allergy or sensitivity, it's best to consult with a healthcare professional.

How Is an Onion Allergy Diagnosed?

The diagnosis of an onion allergy is conducted through a series of tests by an allergist. These tests help to identify specific allergens causing reactions and rule out other potential causes of the symptoms.

Skin Prick Test

A skin prick test (SPT) is the most common diagnostic tool used to confirm an onion allergy. During the test, a small amount of onion extract is applied to the skin via a tiny prick or scratch. If a raised bump or hive appears at the site, it indicates a possible allergy.

Blood Test

A blood test can also be used to measure the amount of Immunoglobulin E (IgE) antibodies in the blood. These antibodies are produced by the immune system in response to allergens. If the IgE levels are high, it suggests an allergic reaction. However, it's important to note that a positive result does not always mean you will experience symptoms.

Elimination Diet and Food Challenge

In some cases, an elimination diet followed by a food challenge may be recommended. This involves removing onions from your diet for a period of time and then reintroducing them under medical supervision. This process helps to determine if onions are indeed the cause of your symptoms.

It's important to consult with a healthcare professional for a thorough diagnosis. Misdiagnosing a food allergy can lead to unnecessary dietary restrictions or exposure to harmful allergens. Similar to the allergy to mold, timely diagnosis and proper treatment are necessary to manage the symptoms effectively.

What Are the Treatment Options for an Onion Allergy?

The treatment options for an onion allergy primarily involve managing symptoms and preventing exposure. However, some treatments can help reduce sensitivity to the allergen over time. It's important to consult with a healthcare professional to understand the best course of action.


Antihistamines can help to alleviate mild to moderate allergic reactions by blocking the action of histamine, a chemical your body releases during an allergic reaction. These are generally available over-the-counter (OTC) and can be used as needed when symptoms occur.

Sublingual Immunotherapy

Sublingual immunotherapy (SLIT) is a treatment method that involves placing a tablet containing a small amount of the allergen under the tongue. This helps your immune system get used to the allergen over time, which can reduce the severity of the allergic reaction. SLIT has been effective in treating various allergies, such as orchard grass allergy and kochia allergy.


The most effective way to manage an onion allergy is to avoid consumption and exposure to onions. This includes being aware of the presence of onions in processed foods and meals.

It's worth noting that while these treatment options can help manage symptoms, they do not cure the allergy. The aim is to make the allergy more manageable, much like handling other common allergens, such as those prevalent during the Iowa allergy season. Remember, it's crucial to seek professional medical advice before starting any new treatment.

What Other Alliums Could Cause Allergic Reactions?

Other members of the Allium family, which includes onions, can also cause allergic reactions. Allergies can occur not only from consumption but also from handling or inhaling airborne particles from these plants.

Garlic Allergies

Garlic is one of the most common Alliums that cause allergic reactions. Symptoms can range from mild skin irritation to more severe respiratory issues.

Leeks, Chives, and Shallots

Other Allium family members such as leeks, chives, and shallots can also trigger allergies. As with onion allergies, symptoms can vary from mild to severe, depending on the individual's sensitivity.

Preventing exposure to these Alliums and managing symptoms with medications can help control the allergic reaction. It's also important to consult with a healthcare professional for guidance and treatment options.

How to Prevent an Allergic Reaction to Onions?

To prevent an allergic reaction to onions, the most effective strategy is to avoid consuming or handling onions. However, this can be challenging as onions are a common ingredient in many dishes.

Educate Yourself about Food Ingredients

Increase your awareness of food ingredients. Many processed foods and restaurant dishes may contain onion as a hidden ingredient. Reading labels and asking about food preparation can help prevent accidental exposure.

Use Substitute Ingredients

In recipes, you can use substitutes for onions, such as celery, bell peppers, or herbs and spices. These can provide similar flavor profiles without triggering an allergic reaction.

Wear Protective Coverings

When handling onions, wearing gloves and eye protection can prevent skin and eye contact, reducing the risk of a reaction.

When Should You Consult a Doctor for an Onion Allergy?

You should consult a doctor for an onion allergy if you experience symptoms after consuming or handling onions, especially if these symptoms are severe or persistent. Early diagnosis can aid in managing the allergy effectively and prevent potential complications.

Persistent Symptoms

If you consistently experience symptoms such as itching, swelling, or gastrointestinal issues after consuming onions, it's essential to seek medical attention. These symptoms could indicate a more severe allergic reaction.

Severe Reactions

In case of severe reactions, like difficulty breathing or anaphylaxis, immediate medical attention is crucial. Remember, anaphylaxis is a life-threatening condition that requires emergency treatment.

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Frequently Asked Questions

What is in onions that makes me sick?

Onions contain fructans, a type of carbohydrate, that can cause digestive discomfort in some people. This can trigger symptoms like bloating, gas, stomach cramps, or diarrhea. Also, some people may have an onion allergy, causing symptoms like nausea, vomiting, or other allergic reactions.

How long does it take to get a food allergy after eating?

Food allergy symptoms typically appear within a few minutes to up to two hours after eating the offending food. However, the time frame can vary based on the individual’s sensitivity and the quantity of allergen ingested. Immediate medical attention is advised for severe reactions.

How can you overcome onion intolerance?

Onion intolerance can be managed by avoiding onions in your diet, using onion alternatives in recipes, and taking digestive enzymes that aid in breaking down food substances that cause intolerance. Some individuals also find relief through allergen immunotherapy, which gradually builds tolerance.

Why can't I eat onions anymore?

If you find that you can no longer eat onions without experiencing discomfort, it's likely that you've developed an intolerance or allergy to them. This can result in symptoms like bloating, heartburn, or digestive upset after consuming onions. It's advisable to consult a healthcare professional for confirmation.

Is it possible to be allergic to only raw onions?

Yes, it is possible to be allergic only to raw onions. This is due to certain proteins that are present in raw onions but become denatured or broken down during the cooking process. Symptoms can include itching, swelling, hives, and in rare cases, anaphylaxis.

How do you treat an onion allergy?

Onion allergy is primarily managed by complete avoidance of onions in any form. For accidental exposure, antihistamines can help alleviate symptoms. In case of severe reactions like anaphylaxis, immediate medical attention is needed. Consultation with an allergist can also provide personalized treatment strategies.

Is there a pill for onion allergy?

Currently, there is no specific pill available for onion allergies. However, antihistamines can help alleviate the symptoms. If you have an onion allergy, it's crucial to avoid onions and seek immediate medical attention if you experience severe reactions, such as anaphylactic shock.

Can you use an EpiPen for an onion allergy?

Yes, an EpiPen can be used for a severe onion allergy. If a person is having an anaphylactic reaction caused by onion exposure, an EpiPen can deliver a potentially life-saving dose of epinephrine. However, it's crucial to seek immediate medical attention afterwards.

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