1. Home  
  2. Health  
  3. Nutrition  
  4. Food allergies  
  5. Developing an allergy

Developing an allergy

Food allergies occur when the immune system overreacts to food proteins known as “allergens.” These hypersensitive reactions can be immediate or delayed, limited or generalized.

Allergies develop when the immune system mistakenly identifies proteins (“allergens”) as health threats.

When you are exposed to an allergen for the first time, your immune system develops antibodies. This is how the sensitization period begins. During this period, you may not show symptoms.

If you are exposed to the allergen again and you are allergic to it, your body will release antibodies and chemicals, triggering adverse symptoms that can be serious or even fatal.

Allergic reactions occur after you ingest or inhale the food you are allergic to. They can also occur if your skin comes into contact with the food.

Allergies can occur at any age, but they are especially common in children, appearing most often before the age of 4. Many children grow out of their allergies before they reach adulthood.

According to Health Canada’s estimates, six percent of babies, three percent of children and one to two percent of adults have one or more food allergies.

Exposure to allergens

We are exposed to food allergens on countless occasions. Here’s what you need to know:

Cooking and allergens

Many allergens, like peanut, fish and crustacean proteins, retain their allergenic properties even when cooked. This means that cooking does not guarantee that the allergens will be destroyed, especially since there are many different ways to cook food, including grilling, frying and steaming. Therefore, cooked food can still trigger an allergic reaction.


If you have a food allergy, you should not eat oil made from a food you are allergic to. There is no guarantee that the allergens will be completely removed from the oils, as different extraction and refining processes will lead to different results.

This recommendation applies to refined oils, like peanut oil, and cold-pressed or unprocessed oils, like soybean and sunflower oil. But it’s also important to know that highly refined oils made from food allergy sources are not subject to allergen labelling requirements.

Crustaceans and fish

There is no direct link between an allergy to crustaceans like crab, shrimp and lobster and allergies to fish and molluscs like mussels and oysters. Someone who has a crustacean allergy is not necessarily allergic to fish. The opposite is also true. However, someone who is allergic to shrimp, for example, is highly likely to develop an allergy to other foods in the crustacean family.

Difference between allergies and intolerances

Food intolerances are the result of a reaction from the digestive system, not the immune system. However, symptoms can resemble those of allergic reactions:

  • Diarrhea
  • Vomiting
  • Bloating
  • Stomach cramping
  • Gas

This discomfort can occur several hours after eating the food. The severity of the symptoms is directly linked to how much of the food was eaten. People with intolerances can sometimes handle very small quantities.

Lactose intolerance

Lactose intolerance is caused by having no lactase, or not enough. Lactase is an enzyme that is needed to digest lactose, a sugar that is present in the milk of all mammals.

Lactose intolerance usually occurs in adults. People who are lactose intolerant can eat lactose-free products. They can also add lactase supplements to their food to limit adverse reactions.

To learn more about food intolerance, visit Allergy Quebec’s Food Sensitivities and Intolerances This hyperlink will open in a new window. webpage.

Last update: March 26, 2024


Was the information on this page useful to you?
General notice

You have questions or require additional information?

Please contact Services Québec