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Onions are a popular addition to a wide range of cooked dishes and prepared cold recipes. If you’re allergic to onions or have a food sensitivity to them, you may find that they’re hard to avoid.

Some people have reactions from eating, touching, or smelling raw onions. Others experience symptoms from both raw and cooked onions.

Onions are part of the plant genus allium, along with garlic, shallots, and chives. People who are allergic or sensitive to onions are often allergic or sensitive to other alliums as well. Ornamental alliums (inedible plants) might also trigger a reaction in some people.

Keep reading to learn more about onion allergies, including symptoms, causes, diagnosis, and treatments. We’ll also share a list of onion alternatives that you can use.

Having a true onion allergy is rare. If you’re allergic to onions, your immune system will identify onions, and possibly other alliums, as dangerous substances.

Your body then takes protective measures, including the release of chemicals like histamine. These chemicals can cause symptoms ranging from uncomfortable to potentially life-threatening.

Having an onion sensitivity (or intolerance) is a more common occurrence. Food intolerances (nonallergic food hypersensitivity) are caused by an inability to process and digest specific foods, not by an immune system reaction.

Food intolerances typically cause less severe reactions than food allergies. If you have an onion intolerance, your immune system will not be triggered, but you may experience some of the same symptoms you would if you were allergic.

For this reason, it can often be hard to tell the difference between the two conditions.

If you’re allergic to onions, you may experience one or more internal or external symptoms. These can range from mild to severe. Symptoms can also vary in terms of onset.

Some people experience immediate symptoms upon eating, touching, or smelling onions. Others may not have any symptoms for several hours, or longer.

Symptoms of onion allergy include:

  • hives or a rash anywhere on the body
  • tingling or itching in the mouth
  • swelling of the lips, face, tongue, or throat
  • nasal congestion
  • difficulty breathing
  • nausea and vomiting
  • diarrhea
  • stomach pain
  • cramping
  • gas
  • dizziness or lightheadedness
  • anaphylaxis, although this is rare

Mild symptoms often resolve once the onion is no longer in your system. They also typically respond well to at-home treatments.

If you have severe reactions, such as vomiting or gastric distress that doesn’t stop, dizziness, or trouble breathing, seek immediate medical help.

In some instances, you may continue to experience symptoms of an onion allergy for days after your exposure has passed. This situation might also require a doctor’s care.

Anaphylactic reaction

While rare, an anaphylactic reaction to onion is possible in someone who is severely allergic. This is more likely to occur if the onion is raw, or lightly cooked.

Anaphylaxis is a medical emergency that requires immediate care. Its symptoms include:

  • dizziness
  • confusion
  • sweating
  • trouble breathing
  • swelling in the mouth and throat
  • loss of consciousness

If you’re allergic to onions, you might also be allergic to foods, plants, and substances that contain similar kinds of proteins. This is known as cross-reactivity.

Foods in this category include edible alliums, such as garlic, chives, scallions, and shallots. It may also include mugwort, which is sometimes used as a tea and in Asian cuisine.

Avoiding edible alliums may be challenging, but it’s not impossible. Make sure to read labels, especially on prepared, processed, and packaged foods. Alliums are sometimes referred to as seasonings on labels.

When in doubt, call the manufacturer prior to eating, or avoid foods with unclear labels. Foods to avoid include:

  • salad bar or deli counter salads, including egg salad, tuna salad, and chef salad
  • deli meats
  • salsas, such as pico de gallo
  • frozen entries
  • frozen or premade pizza crust
  • crackers
  • premade soups and sauces
  • flavoring packets
  • chicken, meat, bone, or vegetable broth
  • flavored cheeses

The allium genus belongs to the Amaryllidaceae (amaryllis) plant family. People with onion allergies may also be allergic or sensitive to flowering amaryllis plants, which include ornamental alliums, and many varieties of lilies.

Amaryllis plants often grow from bulbs. There are hundreds of flowering plants in this category. Plants you may be allergic to include:

  • Purple Sensation
  • Globemaster allium
  • Gladiator allium
  • Corkscrew allium
  • Wild onions
  • Wild chives
  • Rock onion
  • Easter lily
  • Madonna lily
  • Tiger lily
  • Orange lily
  • Daffodils
  • Tulips
  • Agapanthus
  • Iris
  • Alstroemeria

The most effective type of treatment depends upon the severity of your allergic reaction. Treatments for onion allergy include:

  • Antihistamines. Antihistamines are available as over-the-counter oral or sprayed medications. These medications block histamine, which reduces or eliminates minor allergic reactions, such as hives, itching, and nasal congestion.
  • Aloe vera. Aloe vera doesn’t reduce histamine in the body, but it can be helpful for calming down itchy hives. You can find it in pharmacies or online.
  • Hydrocortisone cream. Topical use of this over-the-counter medication can reduce itching and inflammation.
  • Epinephrine (EpiPen, EPIsnap, Adyphren). This prescription medication is an auto-injector sold under several brand names. It’s used to treat severe allergic reactions, such as anaphylaxis.
  • Albuterol sulfate inhaler (ProAir, Proventil, Ventolin). This prescription bronchodilator is used to increase the flow of air through the bronchial tubes.

If you’re allergic to onions, avoiding them is the best way to avoid allergy symptoms. Cooking onions reduces the compounds that cause allergic reactions in some people, so eating only cooked onions may help.

Make sure to also avoid edible alliums and ornamental plants that can set off your symptoms. Taking a daily allergy medication, such as an antihistamine, may help — especially during times of the year when mugwort pollen is high.

If you accidentally ingest or come into contact with onion, take an antihistamine or other type of allergy medication immediately.

In cooking, the best alternatives to onions are often other alliums, although you may need to avoid these, too. If so, get adventurous and try these substitutes:

  • Asafetida. This root vegetable comes from a giant fennel plant, and was originally grown in Iran and Afghanistan. It’s also known as hing, and is a low FODMAP food. You can find it in specialty grocery stores, typically in powder form, or online. Asafetida has an oniony-garlicky taste, and is savory and pungent. When cooked, it mellows in flavor. It’s also very potent. Use a tiny pinch to start, and slowly increase the amount, based on the intensity of flavor you want.
  • Fennel. This licorice-scented bulb becomes savory and lush in taste when cooked. It’s slightly oniony in flavor, and also has a buttery texture. You can use it the way you would use scallions, in similar amounts, in cooked recipes. Fresh fennel can be found in grocery stores, and you can buy dried fennel seeds and powder online.
  • Radish. Try using radishes in cold dishes, instead of raw onion, in similar amounts. Radishes have a sharp flavor and pleasingly juicy crunch.
  • Celery. Its taste may not be similar to onions, but its crunch can be satisfying when used as a substitute in tuna, egg, or chicken salad. Chop in the same amount of celery that you would of onion when preparing these foods. You can also use cooked celery in soups and stews.
  • Low FODMAP foods and spices. There are several brands designed specifically for people who wish to avoid onion and garlic. You can check some out here.

A doctor can help you determine if you have an onion allergy, onion sensitivity, or other condition. They’ll take a physical exam, and ask you questions about your symptoms, food intake, nutritional supplements, and lifestyle. It may help to keep a food diary and bring it with you to your appointment.

Your doctor may recommend that you try an elimination diet over the course of five to six weeks, and report back your results. During an elimination diet, you remove every type of food you might be allergic to, and put them back, one by one, to see which causes a reaction.

There are several diagnostic tests for food allergies and sensitivities. Let your doctor know if you’re taking antidepressants, antihistamines, or heartburn medication, as these may affect test results.

Tests you may be given include:

  • Skin prick test. This test is done in a doctor’s office. You’ll be given tiny amounts of potential allergens, injected just under the skin. If you are allergic to any of them, a hive or other type of reaction will occur.
  • Specific IgE blood test. This blood test measures the level of immunoglobulin E (IgE) antibodies you have in your system. Your blood sample is analyzed in a laboratory to determine which allergens you’re sensitive to.

Having a true onion allergy is rare. Having a food sensitivity to onions is more common. Both conditions share certain symptoms, such as gastric distress.

People allergic to onions may also be allergic to garlic and other alliums, such as chives. If you’re allergic to onions, you may also be allergic to certain flowering plants, such as lilies.

Onion allergies vary in intensity from mild to severe. You can manage the condition by learning what vegetables or plants trigger your allergy, and carefully avoiding them.