Food is essential for life, but what happens when your body responds negatively to a particular nutrient or ingredient?
Sometimes seemingly happening out of nowhere, you eat a specific food and have a less-than-enjoyable reaction. The severity can range from mild irritation and discomfort to potentially life-threatening.
Knowing the difference between food intolerance and allergy is potentially life-saving information. In the US, roughly every three minutes, a food allergy will send someone to the hospital.¹
According to a population-based survey of 40,443 US adults, 10.8% had food allergies, and almost twice as many (19%) believed that they were food allergic.²
For those with at least one food allergy, 38% experienced a related emergency requiring a trip to the hospital at some point in their lives.³
Historically, there’s been limited high-quality evidence about the prevalence of food allergies, but it’s well-established that food allergies among children are on the rise, as well as in adults.⁴
In the Western world, an estimated 10% of people have been diagnosed with food allergies.⁵
Food intolerances are also incredibly widespread, affecting an estimated 20% of the population.⁶
So, how exactly do you discern a food allergy from an intolerance? Unfortunately, the answer isn’t easy as the two often present similarly. But here’s what science has established so far.
While both conditions involve a reaction to a particular food, the mechanism of action and the severity of symptoms significantly differ between food intolerances and food allergies:
A negative digestive system response to a particular food causes a food intolerance. People can have multiple food intolerances. In most cases, the associated symptoms are mild and manageable.
Food intolerances, aka food sensitivities, can develop at any age and stage of life and may increase or decrease in severity due to various factors.
An immune system response causes a food allergy to a conventionally non-harmful substance — such as gluten, peanuts, soy, milk, eggs, or shellfish.
Depending on the reaction's severity, food allergy symptoms can be mild, serious, or life-threatening.
In most cases, food allergies become known in childhood due to the common allergens in the standard diet. Peanut butter, for instance.
If you have a severe food allergy, you must inform those around you (including restaurant waitstaff if you go out to eat). In addition to avoiding the allergen, this information can help prevent accidental cross-contamination.
A helpful way to remember the difference between an allergy and intolerance is to recall which bodily system is affected—your digestive or immune systems. Also, intolerance or sensitivity to a chemical in a particular food (such as lactose) does not cause anaphylaxis. However, a dairy allergy could trigger anaphylaxis.
Anaphylaxis or anaphylactic shock is the most severe form of an allergic response. It can constrict your airways and constitutes a medical emergency.
Again, the specific bodily system involved can profoundly impact the severity of a person’s reaction to a particular food. It also is a defining difference in the potential treatment and management of symptoms. Understanding how and why these systems react to trigger foods can go a long way toward reducing symptoms, managing the severity, and getting timely medical help if necessary.
The digestive system is comprised of the mouth, salivary glands, esophagus, stomach, liver, pancreas, gallbladder, and small and large intestines. It is a long pathway from one end of your body to the other.
When you consume food, the following steps occur:⁷
First, food enters your mouth, where it’s broken into smaller pieces by your teeth and saliva.
Next, it travels through the tube connecting your mouth to the stomach (esophagus).
Once in the stomach, it is broken down further by the strong acid in the stomach.
Finally, the food moves into the small and large intestines, where most nutrients and water are absorbed.
Pancreas and liver enzymes are added into the intestines to help with further food breakdown.
In someone with food intolerances, this process runs inefficiently. Commonly, people with food intolerances experience difficulty breaking down the food in their stomachs or intestines. As a result, indigestion can be a sign of food intolerance.
Common underlying causes of food intolerances are enzyme deficiencies, gastrointestinal irritation, or reactions to food additives or preservatives.
Food allergies are a full-blown immune response to a trigger food. In most cases, a food allergy will cause more severe symptoms than a food intolerance, even when eating a tiny amount of the trigger food. For example, for some individuals, just trace amounts of peanuts are enough to induce breathing problems and other severe symptoms.
Much like during an allergic reaction to medicine or exposure to airborne allergens, the following steps happen during an immune-mediated food allergy response:⁸
Before consuming the trigger food, the person’s immune system (composed of various cells and organs) functions correctly. (The primary role of this system is to protect and fight off potentially harmful pathogens).
When a person consumes food (any kind), the immune system creates an associated antibody (also known as an immunoglobulin E (IgE) that acts as a marker for the substance in the body. As a result, more antibodies are produced in people with a food allergy, alerting the body that this substance may pose a potential risk.
After the first exposure, if the person consumes the trigger food again, their immune system can go into overdrive. In most cases, symptoms will develop within two minutes to two hours of consuming the allergy food. Food allergy symptoms can range from mild and manageable to sudden and life-threatening. Two factors involved in the severity are immune system function and how often you’ve had exposure to the allergen.⁹
Although entirely different mechanisms of action cause food intolerances and allergies, they frequently share many of the same symptoms — particularly in mild cases — which is one of the reasons why getting the correct diagnosis can be complicated.
It is common for people with food intolerances to be able to eat a small amount of their trigger food without feeling profound symptoms. But, if they eat a more significant amount of this food, symptoms may begin to appear. Some of the most common symptoms of food intolerance include:
Abdominal bloating and pain after eating a trigger food
Nausea and diarrhea
Excessive flatulence and gas
Headaches and migraines
Heartburn and acid reflux
Short-term loss of appetite
Feeling like your stomach is “off”
In contrast, food allergy symptoms can be triggered by even the slightest exposure to a trigger food (with some people experiencing symptoms from trace amounts of food contamination).
Additionally, a person with a true food allergy will experience symptoms whenever they come into contact with their allergen.
Examples of some of the most common symptoms of a food allergy include:
Gastrointestinal upset, nausea, and diarrhea
Abdominal cramping and pain
The development of hives or skin rashes
A tingly feeling of the mouth, face, or tongue
Coughing and wheezing
Dizziness and lightheadedness
Throat swelling, resulting in difficulty speaking, swallowing, or breathing
Shortness of breath and anxiety
Loss of consciousness
At their most severe, food allergies can cause a life-threatening condition called anaphylaxis that needs to be treated by medical professionals. In most cases, food intolerances will not cause symptoms of this severity.
Anaphylaxis is a medical condition characterized by the sudden onset of severe symptoms in response to an allergen. Approximately 900,000 Americans require emergency medical attention yearly due to food-related anaphylactic reactions.¹⁰
Top foods and triggers that cause anaphylaxis include peanuts, tree nuts and seeds, medications, milk, animal venom, fish, and eggs.¹¹
If anaphylaxis happens emergency medical help is crucial.
Common signs of anaphylaxis include:
Itchiness, redness, or swelling of the skin
Increased sneezing or developing a runny nose
Swelling and tingling of the mouth, tongue, or throat
Difficulty swallowing or talking
Shortness of breath, coughing, wheezing, and chest pain
A weak pulse, feeling lightheaded, or losing consciousness
Abdominal cramping, vomiting, or diarrhea
Dizziness and loss of orientation
If you are with someone who appears to be having an anaphylactic reaction, call 911 for emergency help.
Additionally, check to see if they have an EpiPen (an emergency dose of epinephrine). You can inject it while waiting for paramedics to arrive. Instructions on how to use an EpiPen should be on the device.
Diagnosing each condition is dependent on the mechanism of action that causes symptoms in the first place:
Tools for diagnosing food allergies:
IgE blood test — depending on the food or substance you believe you may be allergic to, IgE tests can confirm a food allergy according to the amount of IgE found.¹²
Skin test — sometimes called skin prick tests, a skin test is another standard diagnostic tool allergists use. It is a relatively painless test by which a small amount of the suspected allergen goes on your arm. Then the skin is punctured with a special needle, causing you to absorb the allergen. If symptoms like redness or hives appear within several minutes, that indicates an allergic response. Often, dozens of different substances will be tested simultaneously, including potential allergens that are not food-related, such as pet dander or pollen.
Food diary — if you haven’t already done so, your doctor might suggest keeping notes about any allergy-like symptoms you have over several days or weeks.
Elimination diet — you might eliminate the suspected allergen from your diet for some time and monitor yourself for several weeks to see how your body responds and whether or not allergy symptoms disappear.
Provocation test — a provocation food challenge is widely regarded as the gold standard for diagnosing food allergies. A doctor or allergy specialist might call for this test if they cannot reach a diagnosis based on blood work or skin testing. Testing must happen in a medical setting with appropriate supervision, equipment, and medication.
Tools for diagnosing food intolerances:
Hydrogen breath test — lactose intolerance is among the few food intolerances with a specialized diagnostic test. The breath test involves drinking a liquid with lactose and collecting a breath sample. Hydrogen and methane levels will be higher than average in lactose-intolerant people. In a meta-analysis about breath test accuracy, participants with high levels of hydrogen also experienced digestive symptoms like bloating and abdominal pain, as well as dizziness, headaches, and fatigue.¹³
Food diary and elimination diets — typically, diagnosing food intolerances relies more on diet tracking. You will either eat or avoid certain foods for an extended period and write down how you feel. If you feel better when you avoid certain foods, you may be intolerant and should continue avoiding them to experience fewer symptoms.
Avoiding contact or exposure to potential food triggers can help significantly reduce a person’s risk of experiencing a reaction. However, here are some additional tips and helpful practices to follow:
Always read food labels — If you eat pre-prepared food, be extra careful about reading the label. In many cases, the foods you are eating may not contain a specific allergen or irritant, but they may be made in a facility that contains these products. If you are looking to avoid even traces of your trigger foods, reading food labels and avoiding foods that are not clear about their manufacturing practices can be a helpful way to reduce your risk.
Be cautious when dining out — When eating out at a restaurant, be sure to speak with your server to express your food sensitivities. If you have a confirmed allergy, be sure to say so, so that the kitchen staff can avoid using potentially contaminated tools to prepare your meal.
Wear a medical alert bracelet — A medical alert bracelet helps first responders act quickly and appropriately, avoiding any confusion or guesswork. If you have a diagnosed food allergy, they’ll quickly see what you’re allergic to, along with your name and emergency contact number.
Carry any needed medications — If you can develop a life-threatening reaction to food, you must bring emergency medication when you leave home. Epinephrine (delivered via an EpiPen) is an excellent resource during an anaphylactic event while waiting for emergency services to arrive. Do your best to bring one in a bag or backpack if you are out, just in case of exposure to your trigger food(s).
Although they can share overlapping symptoms, the causes behind a food intolerance versus a food allergy are quite different, with the former having a connection to the digestive system and the latter with the immune system. Therefore, depending on which you have, the symptoms, reaching a diagnosis, and treatment options will vary. Unfortunately, it’s not yet possible to cure food allergies, so the primary approach to treating a food allergy or intolerance is to avoid the food or foods in question.
Being prepared to use an EpiPen if necessary is also central to treatment. Immunotherapy (exposure therapy) can desensitize a person to their allergen. However, the results and how long it lasts vary—it is not considered a cure. Similarly, it’s unclear to what extent immunotherapy can prevent emergencies or hospitalization. However, it’s exciting to note that researchers continue to work on advancing immunotherapy and other treatment options, such as DNA vaccines, monoclonal antibody therapy, and more.
The information provided is designed to support, not replace, the relationship that exists between a patient/site visitor and their existing health care professional(s).
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Facts and statistics | Food Allergy
Prevalence and severity of food allergies among US adults (2019)
The epidemiology of food allergy in the global context (2018)
Food intolerances (2019)
Your digestive system & how it works | National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Food allergy: Immune mechanisms, diagnosis and immunotherapy (2016)
Frequency of US emergency department visits for food-related acute allergic reactions (2011)
Epidemiology of anaphylaxis in critically-Ill children in the United States and Canada (2019)
Hydrogen and methane breath test in the diagnosis of lactose intolerance (2021)
Hydrogen and methane breath test in the diagnosis of lactose intolerance (2021)
Food allergies: What you need to know | U.S. Food and Drug Administration
Oral food challenge | Food Allergy
The current state of oral immunotherapy | American Academy of Allergy Asthma and Immunology
Food intolerance and food allergy in adults: An overview | UpToDate
Food allergy | World Allergy Organization
Claire Bonneau is a medical writer and certified trauma operating room nurse.
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