In this article, we look at the more familiar type of food allergies and some that are less common. And explain why food allergies are not the same as food intolerance.

You can be allergic to any food but some food allergies are more common than others. Food packaging must make common allergens obvious in the list of ingredients. The same labelling laws cover restaurant menus. But it’s often impossible for food producers to rule out cross-contamination. That’s why you might see voluntary warnings on certain foods, such as “may contain traces of peanuts”.

These 13 ingredients cause 90% of the allergic reactions to food: eggs, cow’s milk, mustard, peanuts, crustaceans and molluscs, fish, sesame seeds, soy, sulphites, tree nuts, wheat and triticale (a hybrid of wheat and rye grains). Sulphites are food preservatives as well as occurring naturally as part of beer and wine-making. Sensitivity to sulphites is a common cause of allergy-like symptoms

Food allergies affect half of Canadian households in some way. It starts when your immune system overreacts to proteins found in something you eat. The immune system’s job is to protect your body against bacteria or viruses that could make you unwell. But sometimes it gets it wrong. It mistakes a particular food for a threat and rushes to your defence. Your body wants to get rid of the allergen as fast as it can. That’s an allergic reaction.

• Triple check every food label: when you buy food, as you put it away at home and before you eat or serve it. It’s easy to miss something at a glance
• Scan the packaging all over (not just the ingredients) for a “may contain…” warning and don’t take the risk if you find one
• If you’re food shopping online look for a filter for allergies
• Encourage even young kids to check labels for any food allergen. It makes great reading practise and soon becomes second nature
• Tell the Canadian Food Inspection Agency (CFIA) if you get food allergy symptoms but there’s no allergen on the label
• Sign up here for CFIA email alerts about product recalls due to allergen contamination. Or follow the organization on Twitter

You don’t get a food allergy the first time you eat peanuts or shellfish or whatever your trigger is. immune system needs to build its defences. It makes antibodies called Immunoglobulin E (IgE). Now you’re sensitized to that allergen. This may happen without you even realizing you’ve been exposed. It doesn’t mean you’ll definitely develop a food allergy but you could.

If you do, the IgE antibodies will fight back whenever you meet the allergen. They’ll tell other cells to release chemicals like histamine. Various fluids and white blood cells also travel to the site of the supposed attack to help. Pretty quickly you’ll feel the typical symptoms of an allergic reaction.

Many people realize they’re having an allergic reaction within minutes or even seconds. And most symptoms show up within two hours.

One exception is a rare type of allergy to red meat that starts after a tick bite. The tick’s saliva can sensitize you to lamb, pork, beef and venison. Allergy symptoms tend to start four to eight hours after a meal and can be severe.

There’s another rare type of food allergy where the allergic reaction can start more slowly too – days later sometimes. Read more about non-IgE-mediated food allergies below.

Allergic reactions to food can range from mild to severe. These are some of the symptoms to look out for:

• Tingling or itching in the mouth
• A raised, itchy red rash (hives) – sometimes the skin can turn red and itchy but not raised
• Swelling of the face, mouth, throat or other parts of the body
• Difficulty swallowing
• Wheezing or shortness of breath
• Feeling dizzy and lightheaded
• Feeling sick (nausea) or vomiting
• Abdominal pain or diarrhea

The same person can react differently on different occasions. You may feel a bit unwell one time but need immediate medical treatment another. That’s why it’s important to see your family doctor if you suspect you may have a food allergy.

Have you heard of anaphylaxis (pronounced an-a-fi-LAK-sis)? It’s a sudden and severe and often sudden allergic reaction that can be life-threatening. Having this type of reaction once increases the chances of it happening in the future. So does a family history of severe reactions and having asthma or allergies. Call 911 if you spot the warning signs and symptoms of anaphylaxis:

• Skin reactions, including hives and itching and flushed or pale skin
• Low blood pressure (hypotension)
• Constriction of your airways and a swollen tongue or throat, which may cause wheezing and trouble breathing
• A weak and rapid pulse
• Nausea, vomiting or diarrhea
• Dizziness or fainting

Some people can get these symptoms if they play sports after eating a food they’re allergic to. It’s called food dependent exercise related anaphylaxis and luckily it’s fairly rare.

This type of food allergies do not involve IgE antibodies. Protective white blood cells called T cells lead the allergic reaction. Symptoms often affect your skin and your digestion. You may get heartburn, indigestion, vomiting or diarrhea hours or even days after eating.

That’s why this type of cross-reactivity is called pollen food syndrome (PFS). Another name is oral allergy syndrome (OAS). It happens because the food contains a protein very like the one in your problem pollen. Say ragweed pollen gives you hay fever. Well, you might get a mild local reaction in your lips, mouth, or throat when you eat cucumber.

People might experience pollen food syndrome when eating foods such as almonds, hazelnuts, peanuts, and soybeans. But these are also major causes of food allergy. So talk to your family doctor straightaway if it happens.

There is also a rare type of cross-reaction between cat allergens and pork. It usually happens quickly, has the same symptoms as IgE food allergies and can be life-threatening. It’s a reaction called pork-cat syndrome.

Certain fruit, vegetables, nuts and spices can make your lips tingle without being your main allergy trigger. The root cause is actually pollen allergy. That’s why this type of cross-reactivity is called pollen food syndrome (PFS). Another name is oral allergy syndrome (OAS). It happens because the food contains a protein very like the one in your problem pollen. Say ragweed pollen gives you hay fever. Well, you might get a mild local reaction in your lips, mouth, or throat when you eat cucumber.

People might experience pollen food syndrome when eating foods such as almonds, hazelnuts, peanuts, and soybeans. But these are also major causes of food allergy. So talk to your family doctor straightaway if it happens.

There is also a rare type of cross-reaction between cat allergens and pork. It usually happens quickly, has the same symptoms as IgE food allergies and can be life-threatening. It’s a reaction called pork-cat syndrome.

This will show if you’re sensitized to any food allergens. The family doctor will ask about your symptoms and family history before making a diagnosis. It can be helpful to keep food and symptom diary.

Non-IgE food allergies are harder to diagnose. Your healthcare provider may suggest an oral food challenge. This involves giving you increasing amounts of an allergen while watching for symptoms. Or they may want to do an internal examination with a camera (endoscopy). It depends on your medical history.

Allergy testing can’t tell you if you have a food intolerance. That’s when your body struggles to digest a substance such as histamine, lactose, or gluten. It’s nothing to do with the immune system.

Food intolerance symptoms are usually mild to moderate. They also tend to start more slowly than with food allergies. You may even find you can eat a small amount of the problem food without feeling unwell. In food allergies, a tiny trace can cause a reaction. The usual way to diagnose a food intolerance is with an elimination diet. But there are breath and blood tests to identify lactose intolerance.

Allergy testing can’t tell you if you have a food intolerance. That’s when your body struggles to digest a substance such as histamine, lactose, or gluten. It’s nothing to do with the immune system.

Food intolerance symptoms are usually mild to moderate. They also tend to start more slowly than with food allergies. You may even find you can eat a small amount of the problem food without feeling unwell. In food allergies, a tiny trace can cause a reaction. The usual way to diagnose a food intolerance is with an elimination diet. But there are breath and blood tests to identify lactose intolerance.

Don’t change your diet without talking to your family doctor or allergist. They’ll work out a treatment plan with you. This is likely to be a mixture of avoiding your triggers and treating the symptoms when you haven’t been able to. Antihistamine blocks the effect of the histamine your body releases as part of an allergic reaction. It is a common treatment for milder allergy symptoms. Ask your pharmacist for advice about the different types available over-the-counter.

If your family doctor thinks you’re at risk of a severe reaction they’re likely to prescribe an auto-injecting adrenaline pen to carry with you at all times. You could also think about wearing an allergy necklace or bracelet so people know how to help you in an emergency.

1. Check non-food products: Skincare, cosmetics, petfood, vitamins, even modelling clay and finger paint can all include food allergens.

2. Be allergy aware when eating out: Get in touch with the restaurant beforehand to discuss exactly what you need from them not to have an allergic reaction. Help-yourself food counters like salad bars are best avoided. Other customers may have double-dipped the cutlery in something you’re allergic to.

3. Plan ahead when you travel: Tell the airline about your food allergies and order a special meal if you can. On trains and buses take your own food. Pack allergy medications in carry-on luggage in case of emergencies (plus spares in your suitcase). It’s sensible to have both your prescription and a doctor’s letter on you; you may need to explain why you’re carrying meds. Breathing in food allergens is unlikely but you could pick them up on your hands from tables or armrests. So bring cleaning wipes. Translation cards or an app may help you identify allergens in a foreign country.
4. Take care in the kitchen: Store food for someone with allergies on its own shelf and label containers. Clean surfaces, pots and pans, utensils and the microwave with a disposable wiper. Allergens can linger on sponges. Try always to eat at the table. And of course always wash your hands.
5. At school: Create an allergy action plan with your child’s school or care provider. And make sure your child knows all the forms of food and drink their allergen could appear in. Give them the confidence to ask adults about a food if they’re in any doubt. And to ask for help if they start feeling unwell – including with vomiting or diarrhoea.
6. Allergens exist in saliva too: Studies suggest that traces of peanut can linger in saliva for a few hours. So never share cutlery or drinking cups if you have food allergies. And at the risk of spoiling that first kiss, tell your date about your allergy first.

The best general rule is to wash your hands with soap and water before eating or putting your hands near your face. And any time you think you may have been in contact with allergens.

Children may outgrow allergies to milk and other common early triggers such as eggs, soy and wheat. But peanut and tree nut allergy are more likely to stay with you into adulthood.

One way to help prevent food allergies starting in the first place may be to introduce babies to peanuts and other trigger foods much earlier. Allergy experts think starting from six months old or before might encourage the immune system to accept the allergens in later life. Talk to your family doctor or allergist first, especially if food allergy runs in your family or your baby has eczema (atopic dermatitis). Both make it more likely a child could develop food allergies.

Your immune system goes on learning and adapting to new threats throughout your life. This means your allergy can change too. There’s a name for it – the allergic march. Just as kids can outgrow food allergies, grown-ups sometimes get them for the first time too.

The most common triggers for adults are shellfish and fish as well as peanuts and tree nuts. People having their first allergic reaction later in life often think it’s food poisoning. But you know now that vomiting and diarrhoea can be symptoms of food allergy too. So why not speak to your doctor just in case.