Allergy vs intolerance: What’s the difference?

Group of commonly known allergens on a table, including eggs, milk, nuts and pasta.
(Image credit: Getty Images)

If you have an unpleasant reaction every time you eat a certain food, you may wonder whether you have some form of a food sensitivity. But what’s the difference between an allergy vs an intolerance, and how can you identify which one you might be suffering with?

It’s easy to get confused, as these conditions present themselves in similar ways. Food allergies and food intolerances may appear in response to the same dietary triggers, and they both produce similar symptoms, such as stomach cramps, diarrhea and skin rashes. But the underlying mechanisms behind these conditions couldn’t be more different, and getting the right diagnosis is essential if you want to receive the right treatment.

In this article, we’ll answer all of your important questions about food allergies vs intolerances, from causes through to treatments.  

What is a food allergy?

According to the American Academy of Allergy, Asthma and Immunology, a food allergy is a chronic condition involving an abnormal reaction to an ordinarily harmless substance. A typical example would be milk allergy. Your immune system views the allergen as an invader and initiates a chain reaction to ‘neutralize’ it. It prompts white blood cells to produce what are known as IgE antibodies, which attach themselves to cells in our body, causing a release of potent chemicals. One of these chemicals is called histamine. 

When the level of these chemicals starts rising rapidly, we experience a range of unpleasant or even dangerous symptoms. Common signs include itching in the nose, roof of the mouth, throat and eyes, runny nose and tearing eyes. Food allergies may present with vomiting, diarrhea and breathing problems immediately after ingesting a substance too.

In severe cases, a person affected may go into anaphylactic shock. This is a potentially life-threatening condition that can be cured with an immediate shot of a drug called epinephrine.  

man scratching his arm

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According to a review in Clinical Reviews in Allergy & Immunology, there are three types of food allergy: IgE mediated, mixed, and non-IgE mediated. They present different symptoms and require different diagnostic tests. Non-IgE-mediated food allergy includes a wide range of diseases, such as atopic eczema, inflammation of the digestive tract, esophagitis and celiac disease. Symptoms usually start appearing early on, with researchers suggesting that up to 20% of infants may suffer from one of these conditions. The most common food allergies in children include milk, egg, soy, wheat, peanuts, tree nuts, fish, and shellfish. Milk and egg allergies are usually outgrown, but nut allergies tend to persist. 

According to data, at least 26 million US adults have a food allergy. However, they're not spread evenly across the population. Electronic health records suggest that the prevalence of food allergies and intolerances may be almost twice as high in females than males, and that Asian ethnicities seem to be the most affected group.

What is a food intolerance?

According to the American Academy of Allergy, Asthma and Immunology, a food intolerance occurs when a person has difficulty digesting a particular food nor nutrient. A typical example would be lactose intolerance. This can lead to symptoms such as intestinal gas, abdominal pain or diarrhea. Based on the data from multiple studies, food intolerances may affect up to 20% of US adults. 

Scientists point at pharmacological effects of food components, non-celiac gluten sensitivity or enzyme defects as potential causes of this chronic condition. There is also a growing understanding of the role that short-chain fermentable carbohydrates (FODMAPs) may play in triggering symptoms. Food intolerances are commonly linked to irritable bowel syndrome, but as scientists from the Nutrition Journal point out, there’s no conclusive evidence that this is the case. 

The three most common food intolerances are lactose intolerance (a type of sugar found in dairy products), casein intolerance (a type of protein found in dairy products) and gluten intolerance (a type of protein found in grains such as wheat, rye, and barley). 

What is a food sensitivity?

According to Harvard Medical School, food sensitivities encompass unpleasant symptoms that routinely happen after you’ve eaten specific foods, but they’re not related to food intolerances, food allergies or celiac disease. A typical example would be caffeine sensitivity. There is a lot of controversy surrounding these conditions, as not much is known about their origins. It appears that exposure to specific foods may trigger a strong non-allergic immune reaction that in turn generates symptoms such as joint pain, stomach pain, fatigue, rashes, and brain fog. These symptoms are not life-threatening, but they can significantly affect your quality of life.

Food sensitivities are not permanent conditions and they can diminish after some time. It’s been suggested that the reduction or increase in symptoms may be due to changes in the functioning of our immune systems or the composition of our gut bacteria.

woman suffering from lactose intolerance

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Diagnosing an allergy

Diagnosing an allergy, food intolerance or food sensitivity can involve several steps. Your doctor is likely to ask you questions to get a better understanding of your personal and medical history. They may perform a physical exam, and you may be asked to undergo a lung function test to detect how well you exhale air from your lungs. In certain cases, an X-ray of your lungs or sinuses may be needed.

Skin tests

Skin Prick Test (SPT) can be one of the most accurate and least expensive ways to confirm your susceptibility to allergens. A small drop of the possible allergen is placed on a patch of skin that is then lightly pricked or scratched with a needle. If you are sensitive to the allergen, within 15 minutes you will develop symptoms such as redness, swelling and itching. You may also see the affected area raised and inflamed (the so-called ‘wheal’). In general, the larger the wheal, the more likely you are to be allergic to the substance. However, a positive result alone does not indicate a diagnosis. 

Patch tests

Patch tests are used to determine which allergens may be causing contact dermatitis. A small amount of a possible allergen will be placed on your skin and then covered with a bandage. Your doctor will check for any possible skin reactions after 48 to 96 hours.  

Blood tests

 Blood tests tend to be used when you have a skin condition or are taking medicine that interferes with skin testing. Your blood sample will be measured against the amount of antibodies your blood cells produce to neutralize the allergens. This test is called Specific IgE (sIgE) Blood Testing (sometimes referred to as RAST or ImmunoCAP testing). Although it may sound like a reliable and accurate method, blood tests produce a lot of false positive results so can’t be used to diagnose an allergy alone.

Challenge/ Provocation Tests 

Challenge tests are done under close supervision of a qualified medical professional. You inhale or eat a small amount of allergen and a physician monitors your reaction, stepping in if you start going into anaphylactic shock. Since provocation tests carry a large risk to your health, certain conditions have to be met before you’ll be allowed to do them. 

Allergy treatment

The most effective way to avoid the symptoms of food allergies is to remove the allergens from your diet and immediate surroundings. According to The Food Allergy Labeling and Consumer Protection Act of 2004 (FALCPA), food manufacturers based in the United States must clearly state on the packaging whether their product contains any of the eight most common food allergens: milk, egg, wheat, soy, peanut, tree nut, fish and crustacean shellfish. When a food item was made without using these allergens, producers must signal whether there was a chance of cross-contamination during the production process. 

You need to remain vigilant, particularly if you have a severe allergy that increases your risk of going into an anaphylactic shock. Make sure to carefully check food labels, learn what you need to avoid and always ask for a list of potential allergens when dining out. Also, be mindful that you may come into contact with allergens in cosmetics, hair products and other health and beauty aids.


Going into an anaphylactic shock is extremely dangerous and the only effective treatment is an immediate epinephrine (adrenaline) shot. That’s why many food allergy sufferers are prescribed emergency epinephrine auto-injectors, commonly referred to as EpiPens. It’s good practice to always have two doses available to hand, as this severe reaction can recur in about a fifth of affected individuals. 

Adrenaline needs to be injected as soon as you start experiencing symptoms such as trouble breathing, coughing, dizziness, hives, tightness in your throat, rashes, vomiting, diarrhea or abdominal pain. 

Diagnosing and treating food intolerances

Managing food intolerances and sensitivities can be more complicated than food allergies. You may need to spend a lot of time observing your body and experimenting with your diet. One strategy is to remove the foods you believe may be causing adverse reactions for a two to four week period, and then reintroduce them to watch for potential symptoms. 

It’s advised to have a qualified medical professional or nutritionist monitor your progress and guide you on your path to recovery. You may need to stick to a strict diet to make sure your negative symptoms don’t come back. 

There’s also evidence that targeting your gut health could help aid your food intolerances. Maintaining a gut-friendly diet and taking probiotics helps many sufferers keep their conditions at bay. 

According to a review published in the Critical Reviews in Food Science and Nutrition, live bacteria and yeast supplements may ease the symptoms of lactose intolerance. There’s also evidence that regular probiotic consumption can help people with gluten sensitivity, as indicated in the Current Opinion in Clinical Nutrition and Metabolic Care journal.     

This article is for informational purposes only and is not meant to offer medical advice.

Anna Gora
Health Writer

Anna Gora is a health writer at Live Science, having previously worked across Coach, Fit&Well, T3, TechRadar and Tom's Guide. She is a certified personal trainer, nutritionist and health coach with nearly 10 years of professional experience. Anna holds a Bachelor's degree in Nutrition from the Warsaw University of Life Sciences, a Master’s degree in Nutrition, Physical Activity & Public Health from the University of Bristol, as well as various health coaching certificates. She is passionate about empowering people to live a healthy lifestyle and promoting the benefits of a plant-based diet.