I get so many questions regarding allergies and intolerances, so I decided it was time to write a post about it!
People are often not sure on how to go about getting a proper diagnosis, and there is a lot of self-diagnosing going on. As a dietitian, I recommend as varied a diet as possible, so will always recommend that people seek advice from a qualified professional who uses recognised diagnosis methods to avoid them cutting out foods unnecessarily.
Reactions to foods are common, but most are caused by an intolerance rather than an allergy. Let’s start at the beginning and understand the difference between an allergy and an intolerance.
The difference
A true allergy is defined as “a response of the body’s immune system to a normally harmless substance”. The key word here is IMMUNE system. When someone has a true allergic reaction, this triggers an immune response, or, in other words, the body releases histamine. The release of this histamine will in turn cause a series of reactions which present themselves as symptoms. The presence and nature of these symptoms plays a key part in determining the diagnosis.
An intolerance does not involve the immune system, and therefore does not trigger the release of histamine. An intolerance can be triggered by various things, such as missing crucial enzymes needed to digest foods (as in lactose intolerance), IBS (see my post on irritable bowel syndrome here) or increased sensitivity to naturally occurring substances or food additives.
Symptoms
People who have an intolerance can often consume a small amount of the food and not experience any symptoms, whereas those with allergies can have severe reactions even to small amounts. Allergic reactions can also get progressively worse the more times the person consumes that food.
Allergic reactions are caused by the release of histamine, and generally happen quite soon after the offending food has been consumed. Typical allergic symptoms include; a bumpy, red rash formed around or inside the mouth, tingling or itching around the mouth and throat or swelling of the lips, tongue or throat. In severe cases, people can go into anaphylaxis, which can be life threatening.
Symptoms associated with an intolerance are likely to be less serious than allergic symptoms, take longer to appear* and are often linked to digestive problems. However, this does not mean that they are unimportant. Intolerance symptoms can be debilitating and very uncomfortable for the individual. Typical symptoms include; bloating, abdominal pain and diarrhoea.
*To complicate things a little bit further, there are different types of allergies, IgE and IgG. IgE allergic reactions tend to cause immediate onset of symptoms. However, IgG symptoms can take much longer to develop, sometimes several days. People with allergies often experience a mixture of both types of symptoms. This is why it’s important to get the opinion of a qualified professional so that they can help you determine the nature of your allergy.
Diagnosis
If you think that you, or your child, may have a food allergy or intolerance, the first thing to do is to make an appointment with your GP. When you speak to your GP, they will ask you several questions to help determine the type of reaction you are having. Questions may include what type of symptoms, how long they took to appear, how long they lasted and also whether there is a family history of allergies. Sometimes it helps to begin keeping a food and symptom diary when you suspect an allergy to help you answer these questions!
If your doctor suspects an allergy, there are then a couple of options depending on the symptoms. The best, most accurate diagnosis is likely to come from a combination of your clinical history and the following tests:
Skin-prick test. This is where small amounts of the suspected allergens (foods likely to cause a reaction) are placed into the skin on the forearm. If the skin-prick becomes red, itchy or swollen, this indicates a positive reaction. This test is painless but should be carried out an an allergy centre or doctors clinic, due to it carrying a slight risk of anaphylaxis if your reaction is severe.
Blood test. This involves testing a sample of your blood for presence of certain anti-bodies.
Food elimination. As the name suggests, this is when you cut out the food that you suspect is causing the reaction from your diet. After a period of about 2-6 weeks, the food should then be reintroduced. If the symptoms disappear during the time when you’re not eating the food, and reappear on its reintroduction, then this can be used as a diagnosis. Before starting such a diet, you should seek advice from a dietitian to ensure that you are not losing out on nutrients by eliminating the offending food(s).
Non-evidence based testing. There are some shops that sell kits for allergy testing or outlets that offer testing hair/blood samples for presence of allergens. The principles on which these tests claim to be based are unproven, and research into their effectiveness has found them unreliable.
Unfortunately, tests used for diagnosing food intolerance (with the exception of lactose intolerance) are not always reliable. Some practitioners use IgG blood tests as a result for intolerances, however the evidence is patchy and most allergy specialists consider IgG results unhelpful in isolation.
It is also important to note that none of the allergy tests above are 100% conclusive all of the time. Usually, these tests are used in combination with your clinical history and symptom description. Your GP or doctor will probably have his suspicions upon talking to you, and then the tests will sometimes be used to confirm the diagnosis.
Again, because of the significance of clinical history in diagnosing allergies/intolerances, you can appreciate how important it is to involve a qualified professional.
More information
Jen Credicott | Dietitian 
My younger son was born with a long list of food allergies. Thankfully many of the most serious have diminished in severity or gone away entirely over the last seven years. I often get frustrated by moms who have self-diagnosed their kids with certain allergies. For a parent, allergies can be scary and going out to eat is very nerve wracking. I always encourage moms to go to the allergist for testing because I would never want to see a child go through the limitations of an allergy if they really did not have a true allergic response.
So very true. I’m glad your son’s allergies have improved over time! Thank you for your comment.