Most people assume that a food allergy or intolerance is something you get as a kid. It may be something you live with for the rest of your life, or could be something you grow out of. But did you know you can randomly develop food allergies as an adult, too. You can even develop an allergy or intolerance to foods you’ve eaten for years with no problem.

There is a difference between an allergy and an intolerance. Both cause reactions to and in the body, but the severity and implications are different. For starters, an allergy can be fatal whereas intolerances cause more discomfort. Food allergies are just like any medical condition—something decides to go haywire and the next thing you know that peanut butter you love so much is now making you sick.

A food allergy occurs when a person's immune system reacts to allergens that are harmless to other people. Most food allergies are caused by peanuts, tree nuts, milk, eggs, sesame seeds, fish and shellfish, soy, lupin and wheat. Food intolerances are adverse reactions to foods that occur in a small proportion of the population. These reactions are not the same as allergies, but may include rashes and swelling of the skin, asthma, and stuffy or runny nose, irritable bowel symptoms, colic, bloating, and diarrhoea, migraines, headaches, lethargy, and irritability.

Food allergies develop after you are exposed to a food protein that your body thinks is harmful. The first time you eat the food containing the protein, your immune system responds by creating specific disease-fighting antibodies (called immunoglobulin E or IgE). When you eat the food again, it triggers the release of IgE antibodies and other chemicals, including histamine, in an effort to expel the protein "invader" from your body. Histamine is a powerful chemical that can affect the respiratory system, gastrointestinal tract, skin or cardiovascular system.

The allergy symptoms you have depend on where in the body the histamine is released. If it is released in the ears, nose and throat, you may have an itchy nose and mouth, or trouble breathing or swallowing. If histamine is released in the skin, you may develop hives or a rash. If histamine is released in the gastrointestinal tract, you likely will develop stomach pains, cramps or diarrhea. Many people experience a combination of symptoms as the food is eaten and digested.

There are many aspects that may contribute to food intolerance. In some cases, like with lactose intolerance, the person lacks the chemicals, called enzymes, necessary to properly digest certain proteins found in food. Also common are intolerances to some chemical ingredients added to food to provide colour, enhance taste and protect against the growth of bacteria.

Of course, any food consumed in excessive quantities can cause digestive symptoms. But if you’re worried, go see your GP and get checked out.