An allergy is the body’s extreme reaction to a substance that is usually harmless. A food allergy can be mild, serious or can even cause death. Some people react to a food within minutes, while other reactions may take hours. In general, the more serious the allergy the faster the body reacts. The substance that causes an allergic reaction is called an allergen. When a person has an allergic reaction to food:

• The immune system attacks the substance in the food (allergen) as if it were a bad germ.  The fighters in the immune system are called antibodies.
• The antibodies make the body release chemicals to clear the allergen from the body.
• These chemicals can cause swelling and irritation or other problems in certain parts of the body.

What are the symptoms of a food allergy?

The most common symptoms of an allergic reaction to food include:

• Throat, nose and lungs: stuffy or runny nose, asthma, throat swelling.
• Skin: itchy skin or eyes, rashes, hives, eczema and swelling, especially around the mouth and face.
• Stomach: diarrhea, constipation, nausea, vomiting, bloating, stomach pain.
• Other: anaphylaxis (sudden, severe reaction that involves many body systems), failure to thrive, headaches, paleness, dark circles under the eyes.

What is a food intolerance?

Unlike a food allergy, a food intolerance does not involve the immune system. Food intolerance is a general term that describes many types of reactions to food or food additives. For example, you might get an upset stomach from the lactose in milk or the fibre in cereals. The symptoms of a food intolerance can be mild or serious.

Is it a food allergy?

It can be hard to determine if the problem is a food allergy. In some cases, you can simply take the food out of your diet to see if the symptoms go away. In other cases, you may have a hard time finding the cause because many things can cause the same problems. To find out if a problem is a food allergy, follow these steps:

• Visit a doctor to rule out other problems that would cause the same symptoms.
• Keep a diary of all food, drinks, medications or supplements you take and note any reactions.
• Your doctor can decide if you should see an allergist. An allergist might do the following:                    
  • Skin tests. The allergist scratches a small amount of the allergen under the skin. If an itchy bump appears, there has been a reaction. The skin test does not always give a clear response, so it is not always helpful for diagnosing food allergies.
  • Challenge diets. The suspected food is eliminated from the diet until the symptoms go away (about five to 10 days). The foods are slowly added back to see if your body reacts. This diet should be planned with the help of a registered dietitian. You do not usually follow a challenge diet for longer than two weeks.

What are the most common food allergies?

Any kind of food can be an allergen. The most common problem foods are cow’s milk, eggs, nuts, peanuts, fish and shellfish. Other common food allergens are wheat, tomatoes, strawberries, oranges and soybeans.

Should all food allergens be taken out of the diet?

People react differently to food allergens. When reactions are mild, you can occasionally eat a small amount of the problem food. When reactions are more serious, even smelling the food might cause a reaction. Cooking a food can sometimes help but fish, nuts and peanuts should be avoided in any form if you know they cause an allergic reaction.

If food allergies are a problem:

• Avoid the food that causes the problem.  If you must avoid many foods, a registered dietitian or a community health nutritionist can help you plan a balanced diet.
• Learn to read labels. Other forms of the food are sometimes in packaged foods. For example, casein is a milk protein that may cause problems for people with a milk allergy.
• Check the ingredients of any medications or supplements before you take them. Ask a pharmacist for help.

Can food allergies be prevented?

Food allergies probably cannot be prevented but certainly can be delayed. If you do not have a family history of food allergies, eat a balanced diet by choosing healthy foods from Canada’s Food Guide to Healthy Eating. However, if you have a family history of food allergies, there are some steps you can take to lower the risk for your children:

• If you are pregnant, during the last three months of pregnancy avoid the foods you are allergic to, and reduce the amounts of foods eaten that are most likely to cause allergic reactions.
• Breastfeed for at least the first six months (some sources recommend up to twelve months). Food allergens can be passed to the baby though breast milk. If you have a strong family history of allergies, a more restricted diet may be necessary. You should discuss this with your physician. A registered dietitian can help you plan a balanced diet and can recommend vitamin and mineral supplements if you need them.
• Do not give solid foods until the baby is six months old. Avoid those foods that are most likely to cause allergic reactions until the baby is at least one year old. Avoid eggs until age two. Avoid peanuts, nuts, fish and shellfish until age three.
• When you introduce solid foods to a baby with a family history of food allergies, try one new food every two to three weeks and watch for any reaction.