Food intolerances and food allergies have similar symptoms, but the differences between them are important. If you are intolerant of a certain food, eating it can make you feel very sick. However, if you have a true food allergy, your body’s reaction to that food can be life-threatening.

Food intolerance affects the digestive system and occurs when your body can’t properly break down the food. This can be due to enzyme deficiencies, sensitivity to food additives, or reactions to natural chemicals in foods. People with food intolerance can often eat small amounts of that food without any problems.

Food allergies, on the other hand, involve the immune system. Your immune system is responsible for defending your body. If you have an allergy to a certain food, your immune system sees that food as an invader and overreacts by producing antibodies called immunoglobulin E (IgE). These antibodies cause an allergic reaction by releasing chemicals. Each type of IgE has a specific “radar” for a specific allergen. Unlike food intolerance, even a tiny amount of the allergenic food can cause a serious or life-threatening reaction in a food allergy. This can happen by eating, touching, or inhaling the food.

Allergic reactions to foods usually show symptoms on the skin, such as hives, itchiness, or swelling. Gastrointestinal symptoms like vomiting and diarrhea may also occur. Respiratory symptoms can accompany skin and gastrointestinal symptoms, but they usually don’t happen alone. Anaphylaxis, for example, is the most severe allergic reaction that happens quickly. Symptoms of anaphylaxis may include difficulty breathing, dizziness, or loss of consciousness. Without immediate treatment, such as an injection of epinephrine (adrenalin), and expert care, anaphylaxis can be deadly.

What foods can cause an allergy?
Although it is possible for any type of food to cause bad reactions, approximately 90 percent of all bad reactions can be assigned to eight specific food categories. These are:

Eggs
Eggs are a common cause of allergies in children. Egg allergy can develop in infancy, and most children will outgrow it by adolescence, although not all. Both egg yolks and egg whites contain proteins that can trigger allergies, but allergies to egg whites are more common. Breastfed babies can also have an allergic reaction to egg proteins if their mother consumes eggs. Foods that might have eggs in them are marshmallows, mayonnaise, meringue, baked goods, breaded foods, marzipan, frostings, processed meat, meatloaf, meatballs, puddings, custards, salad dressing, many pastas, and pretzels. Some words on the ingredient list indicate that there are eggs in the food, like albumin, globulin, lecithin, livetin, lysozyme, vitellin, and words that start with “ova” or “ovo,” for instance, ovalbumin or ovoglobulin.

Milk and dairy
Milk allergy is a common immune system response to milk and milk-containing products. It can occur in children and is usually caused by cow’s milk, but it can also be caused by milk from other animals. Cow’s milk has two proteins that can cause allergies: casein and whey. They’re also in some processed foods and other types of milk. Most children eventually outgrow the allergy. Common sources of milk proteins that can cause allergies are found in dairy products, such as whole milk, low-fat milk, skim milk, buttermilk, butter, yoghurt, ice cream, and cheese. Milk can also be present as an ingredient in processed foods like baked goods and processed meats. It may be hidden under names like whey, casein, or ingredients with the prefix “lact,” such as lactose and lactate. Other hidden sources of milk include candies like chocolate, nougat, and caramel, protein powders, artificial butter flavor, artificial cheese flavor, and hydrolysates. Even if a food is labeled “milk-free” or “nondairy,” it is important to carefully read the label as it may still contain allergy-causing milk proteins.

Peanuts
Even a small amount of peanuts can lead to a serious and potentially life-threatening response called anaphylaxis. Peanut allergy happens when the immune system mistakenly sees peanut proteins as harmful. Coming into direct or indirect contact with peanuts causes the immune system to release chemicals that cause symptoms in the bloodstream.

There are different ways that exposure to peanuts can happen:

1. Direct contact: Eating peanuts or foods that contain peanuts is the most common cause of peanut allergies. Sometimes, even touching peanuts can trigger an allergic reaction.
2. Cross-contact: This occurs when peanuts accidentally get into a product. It usually happens during the processing or handling of food.
3. Inhalation: Breathing in dust or aerosols that contain peanuts, such as peanut flour or peanut oil cooking spray, can lead to an allergic reaction.
   Read labels carefully to make sure you don’t accidentally eat something with peanuts in it.

Tree nuts
Tree nuts can cause a serious allergic reaction called anaphylaxis, which can be deadly. If you have a tree nut allergy, it will probably last your whole life. Only a small number of people outgrow it. People often mix up peanuts and tree nuts. Peanuts are not nuts, but legumes. However, studies show that 25% to 40% of people who are allergic to peanuts also have a reaction to at least one tree nut. To prevent an allergic reaction, avoid nuts and nut products. Read labels carefully to make sure you don’t accidentally eat something with nuts in it.

Fish
Unlike other food allergies that are usually noticed in babies and young children, a fish allergy may not show up until you’re an adult. In fact, a study found that up to 40 percent of people who reported a fish allergy didn’t have any problems with fish until they were adults. If you’re allergic to a fish with fins, like tuna, halibut, or salmon, it doesn’t mean you’re also allergic to shellfish like shrimp, crab, and lobster. Some doctors suggest that if you have a fish allergy, you should avoid eating all types of fish and fish products. You should also read food labels carefully to make sure they don’t contain any fish ingredients.

Shellfish
Shellfish allergy is when the body’s immune system reacts abnormally to proteins found in certain marine animals. These animals include crustaceans (such as shrimp, crabs, and lobster) and mollusks (such as squid, oysters, and scallops). Shellfish allergy is a common food allergy. Some people react to all types of shellfish, while others only react to specific kinds. The most common type of shellfish allergy is to crustaceans. Some people may be allergic to only one type of shellfish but can safely consume others. However, some with a shellfish allergy must avoid all types of shellfish.

Wheat
A wheat allergy is when your body reacts badly to foods that have wheat in them. This can happen if you eat wheat or breathe in wheat flour. Wheat allergy is different from celiac disease. With a wheat allergy, your body makes antibodies to proteins in wheat. With celiac disease, a protein called gluten causes a different kind of reaction in your immune system. If you have a wheat allergy, you can be allergic to any of the four types of wheat proteins. Wheat proteins are in many foods, like bread, pasta, cereal, soy sauce, ice cream, and even cosmetics and play dough. If you have a wheat allergy, you might also be allergic to other grains like barley, oats, and rye. But if you’re only allergic to wheat, you don’t have to avoid as many foods as someone with celiac disease.

Soy
Soy is a type of food that is often used in baby food and other processed foods. Some young children are allergic to soy, which means they can have a bad reaction to it. This usually happens to babies and young children under 3 years old, but many grow out of it as they get older. Things that can cause a soy allergy include soy products like soy milk and soy sauce, as well as some baby formulas.

Sesame
The ninth most common food allergy is a sesame allergy. Approximately 20% of individuals eventually overcome their sesame allergy. When buying food products, always read the labels, as manufacturers can change their products at any time. It is also important to be aware of cross-contamination, which occurs when sesame is transferred to a food that does not normally contain sesame. Food ingredients that may indicate the presence of sesame are: benne, sesame oil, sim sim, benne seed, sesame seed, tahini, benniseed, sesamol, tahina, gingelly, sesamolina, til, gingelly oil, sesamum indicum, and vegetable oil.

Sources:
https://www.aaaai.org/tools-for-the-public/conditions-library/allergies/food-intolerance
https://acaai.org/allergies/allergic-conditions/food/
https://www.mayoclinic.org/diseases-conditions/egg-allergy/symptoms-causes/syc-20372115
https://www.mayoclinic.org/diseases-conditions/milk-allergy/symptoms-causes/syc-20375101
https://www.mayoclinic.org/diseases-conditions/peanut-allergy/symptoms-causes/syc-20376175#:~:text=An%20allergic%20response%20to%20peanuts,around%20the%20mouth%20and%20throat
https://acaai.org/allergies/allergic-conditions/food/tree-nut/
https://acaai.org/allergies/allergic-conditions/food/fish/
https://www.mayoclinic.org/diseases-conditions/shellfish-allergy/symptoms-causes/syc-20377503#:~:text=Shellfish%20is%20a%20common%20food,severe%20and%20even%20life%2Dthreatening.
https://www.mayoclinic.org/diseases-conditions/wheat-allergy/symptoms-causes/syc-20378897
https://acaai.org/allergies/allergic-conditions/food/soy/
http://www.nlallergy.ca/for-patients/sesame-allergy