Popular flavor enhancers garlic and onion can trigger allergic reactions. Garlic allergy and onion allergy are uncommon. But it is important to understand the nuances when these common ingredients cause symptoms.
These edible bulbs are mostly known for causing contact allergic reactions, such as skin rashes, or for setting off asthma. Symptoms experienced after consuming garlic or onions might also indicate an intolerance instead of a true IgE antibody food allergy.
So diagnosing allergies to garlic and onions can be difficult. Since these members of the allium family are not among the top 9 major allergens (peanut, tree nut, wheat, milk, egg, soy, shellfish, fish and sesame), they may not be an obvious trigger.
If an allergist confirms you have a garlic or onion allergy, it’s often a challenging condition to manage. Both flavoring agents are widely used in restaurant meals and in packaged foods.
Garlic and onions are used in dishes and packaged products in various forms, such as raw, powdered or oil.
The allium family also includes leeks, scallions, chives, and shallots. Cross-reactivity, when your immune system reacts to allergens with similar proteins, is a possibility.
But having an allergy to one allium vegetable does not necessarily mean you will be allergic to the other, says Dr. Scott Sicherer, director of the Jaffe Food Allergy Institute at New York’s Icahn School of Medicine at Mount Sinai.
How Common is Garlic or Onion Allergy?
The prevalence of allergies to garlic and onion is hard to gauge because there are few studies on these allergies.
“Garlic is commonly used in cooking worldwide yet has rarely been investigated for its allergic potential,” according to one study on self-reported garlic allergy. The University of South Florida researchers, who authored the study, analyzed data from 132 individuals who reported a garlic allergy from May 2017 to October 2021.
The data for the study published in September 2024 was collected through the FARE Patient Registry. The food allergy nonprofit’s registry includes self-reporting on food allergies from over 14,000 participants.
The study identified the largest group of U.S. garlic-allergic patients reported to date, who were mostly diagnosed later in life. They were more likely to have a family history of food allergies compared to other patients in the registry with a single food allergy. The garlic allergy patients also were more likely to have hay fever, asthma, or atopic dermatitis.
The prevalence of garlic allergy in the FARE registry was 1 percent. The study says 34 of those patients reported an allergy to another allium (onion, shallot, leek, scallion and chives).
But that 1 percent does not necessarily reflect the prevalence of garlic allergy in the general population, says study author Dr. Thomas Casale. He notes there are limitations in a study with self-reporting versus testing confirmation.
Garlic allergy is still likely rare, says Casale, chief of clinical and translational research at the University of South Florida’s Division of Allergy and Immunology.
Yet, a 2018 study suggests, “allergic hypersensitivity to garlic and onions should not be underestimated.” That observational study tested garlic and onion extracts in more than 8,000 patients at an allergy clinic in Spain. Almost 3 percent had results indicating hypersensitivity to garlic and onion.
Symptoms of Garlic or Onion Allergy
Sicherer says that in the medical literature there have been less than a handful of reports of anaphylaxis to garlic and onion.
While a severe reaction is rare with these bulbs, they can cause symptoms of an allergic reaction. This occurs when a person’s immune system identifies proteins in a food as an allergen and begins to produce antibodies – called IgE – against that food. These antibodies attach themselves to mast cells, and when the person again eats the allergenic food, the proteins from it become attached to the IgE antibodies. This causes the mast cells to release histamine and other chemicals, which cause the symptoms of allergy.
Food allergy symptoms may include:
• Tingling in the mouth
• Swelling of the tongue and throat
• Itchy skin, hives or skin redness
• Breathing difficulty, wheezing
• Abdominal cramps
• Vomiting
• Faintness due to a sudden drop in blood pressure.
Unlike an IgE-based allergy, an intolerance does not trigger an immune system response. It is more likely to cause mild symptoms and is not life-threatening.
Intolerance symptoms from eating garlic or onion may include:
- Bloating
- Heartburn
- Diarrhea
- Nausea
- Headache
A garlic or onion intolerance can also be related to FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols) foods. The carbohydrates in these foods can be poorly absorbed by some people, triggering irritable bowel syndrome (IBS). Garlic and onion are fructans, that fall under the “O” in FODMAP. Learn more about the FODMAP diet here.
Physical responses to a food’s aromatics are not considered symptoms of an allergic reaction or a cause for concern. For example, Sicherer notes that if your eyes water while slicing an onion that does not mean you are allergic to the onion.
Rashes and Asthma
Garlic and onion are more commonly known for causing occupational allergic issues. Contact dermatitis, an itchy rash caused by direct contact with a substance, is a common result, Sicherer says.
For example, restaurant workers who are chopping onions all day without wearing gloves, might get an itchy rash from the onion’s chemicals seeping into the skin. But the same people suffering a skin rash from handling the onion, might still be able to eat it, he says.
Working with garlic or onion also can trigger asthma episodes, Sicherer says. For example, spice factory workers handling garlic powder are at risk of experiencing asthma symptoms from inhaling the garlic dust.
Nuances with Garlic and Onion Allergy
There are nuances involved with this uncommon allergy that could make it tricky to figure out. Sicherer says someone who is allergic to garlic or onion may react to only the raw or the cooked form, or to all forms. Raw garlic and raw onion seem to cause more reactions than their cooked counterparts, he adds.
For example, someone might react to a raw onion on a hamburger, but have no issues eating onion that is cooked in soup.
The form of garlic or onion could matter, too. For example, cloves of garlic whether cooked or raw could trigger a reaction in some, whereas garlic powder sprinkled on pizza might have no effect.
A small study captured the effect of heat on garlic proteins in two patients who had allergic reactions to garlic. One patient reported symptoms to both raw and cooked garlic, while the other reacted to raw garlic only. The research to date on raw versus cooked “illustrates the need for further studies,” Casale says.
The amount of the allergen also plays a role, Sicherer says. For example, someone could tolerate a bit of garlic powder in ketchup, but experience an allergic reaction to shrimp scampi with a garlicky sauce.
Yet others with a garlic or onion allergy might have to avoid all forms of the allergen.
Detective work gets tricky when dealing with spices. For example, someone could eat steak at home with no problem, but react after eating steak at a restaurant, unaware it had been seasoned with garlic. It can be helpful to keep a food diary to track symptoms associated with certain dishes.
In light of the nuances, there is no one answer about how to manage an allergy to garlic or onion. Sicherer recommends speaking to your doctor for proper testing, diagnosis, and advice on how to proceed. “It’s something that should be discussed on an individualized basis.”
Managing Diet with No Garlic or Onion
Garlic and onion are not required to be labeled specifically because they are not among the top 9 major allergens. They often fall under “spices”, “seasonings” or “flavorings” on ingredient lists.
Calling the manufacturer to find out whether garlic or onion is an ingredient is essential for diet management. When dining out, it’s helpful to carry an allergy chef’s card and to ask about whether dishes contain or are cooked with garlic or onion.
If you have a garlic allergy or onion allergy, be on alert for dishes where they are common ingredients.
Foods to watch include:
- Chutneys
- Pastas
- Boxed rice
- Chilis
- Sauces
- Soups
- Frozen entrees
- Salad dressings
- Butters
- Oils
Instead of garlic and onion, home cooks can flavor their dishes with alternatives such as:
- Cumin
- Chili pepper
- Paprika
- Basil
- Oregano
- Ginger
- Curry
- Horseradish
- Asafoetida (Indian spice, known to taste like onion)
- Fennel
- Bell peppers
- Celery
- Carrots
- Cabbage
It can be tricky to navigate dining with an allergy like garlic or onion. But research into products, creative cooking substitutions, communication about ingredients and your needs can help you safely avoid the allergens.
Related Reading:
Peanut Oil and Allergy: When Is It Safe to Eat, When Is It Not?
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