The most fun part about being a Science Person online is that every once in a while someone will come to you with a question. Lucky me, because I chose to write about health, I tend to get some wonderful and weird ones about the various lumps and bumps that people are worried about.
One thing has cropped up a lot lately: allergy tests. It seems like everyone’s getting them. You can now apparently get allergy tests for everything from tea to boiled eggs — why boiled? Who knows — that will tell you with pinpoint accuracy not just what you are allergic to, but how much of an allergy you have!
If it sounds to good to be true, that’s because it is.
If you’ve had an allergy test, there’s a good chance the results weren’t worth anything at all.
Allergies involve some wildly complicated biochemical reactions in our bodies, but the basic idea is that your immune system attacks something thinking that it’s a problem when actually it’s just pollen or cat fur. Not only that, but your body is hypersensitive to this thing — known as an allergen — which means that you produce an excessive immune response.
Basically, your body goes crazy. And it can be life-threatening.
Notably, an allergy is very different to an intolerance. Allergies are caused by your body over-reacting to an innocuous substance. Intolerances — usually to food — are caused by a vast multitude of issues with the gastrointestinal tract, which is another way of saying that we don’t know exactly how they work.
To test for an allergy, there is essentially one kind of test. You take some of the allergen — say, a bit of peanut — and expose your body to it. You then observe the reaction.
It really is that simple.
There are two ways of doing this. The gold standard method is to use what’s known as a ‘skin prick test’. Basically, a doctor takes some of the allergen, pokes it under your skin, and after a bit of a wait checks to see if you’ve had a reaction. The second method is to put some of the allergen in a blood sample that you’ve had taken, and check for antibodies that your body produces, to see if you blood cells are having a reaction to the allergen. It’s not as good as a skin prick test at identifying allergies, but for people with a life-threatening allergy it’s often better than potentially dying.
The problem is, neither of these tests are definitive. It’s possible to have no reaction to a skin prick test and a negative IgE (antibody) test, and still have an allergy. It’s possible to not have an allergy and still have a reaction to both of these. The problem here is that allergies aren’t perfectly understood, so both of these tests need to be done with caution and only under the advisement of a doctor — ideally, an allergy specialist.
So that’s the science: ideally a skin prick test, and if that’s not possible a blood test that looks for very specific allergy-associated antibodies in your blood. There are a few variations of these tests — for example, instead of pricking your skin the doctor might just put a patch smeared with ‘allergen paste’ on you to test for allergic rashes — but that’s pretty much it.
So what about all the other tests that people are getting?
This is where we move into the vast wasteland of “alternative medical practice”. You see, the tests above are pretty much it as far as allergy testing goes from a medical perspective. There are some specific tests for things like lactose intolerance and coeliac disease, but these aren’t actually allergies. There are some other tests — like a total IgE count — that can give you some information about allergic response, but they won’t tell you if you have an allergy to a specific thing.
But people are spending vast sums of money on tests that are not so well evidenced.
Firstly, there are the pseudoscientific. For example, IgG (different to IgE) tests measure an antibody in your blood, it’s just not useful for identifying allergies because these antibodies can be increased just because you eat more of certain foods. So you drink a lot of tea, get an IgG test, and suddenly someone’s telling you that you are allergic to it! It’s nonsense, but seems very believable, especially if you’ve paid 100’s of dollars for that nonsense.
Another pseudoscientific test is hair analysis. Some practitioners will claim that they can read a vast amount into your life, or even test your DNA, with just a lock of hair. They can’t. This is basically just a scam. Hair is mostly just a bunch of hardened proteins, and there’s no test you can do on it that’ll tell you about your immune system or allergies.
Then comes the total nonsense tests.
I’m not going to go into them all. Some examples are applied kinesiology, reiki, vega testing, electrodermal testing and the like. Suffice to say that if I haven’t mentioned it yet, and it’s not done by an allergy specialist with a medical degree, then there’s no reason to believe that it has any plausibility at all.
The biggest take-home here is that allergy testing is ridiculously complex. Allergy specialists spend a decade in training after medical school so that they can interpret the results of tests alongside symptoms and tell you what’s wrong.
It’s also important to remember that allergies tend to have pretty specific symptoms. Allergic rhinitis — hayfever — is usually limited to two or three problems. If you’re having vague chronic symptoms like fatigue, it’s more likely to be caused by lifestyle factors than an allergy. Alternative practitioners make their money through a simple formula: label every chronic problem an allergy, give you a bogus test (that costs $100s) which is guaranteed to come back positive, and charge you through the nose to ‘treat’ the newly-discovered condition.
If you’re worried about allergies, see a doctor. Better yet, see an allergy specialist. They spend years learning the science behind allergies so that they can diagnose and treat them.
Just don’t spend hundreds of dollars on a dodgy test.
It might not tell you much about your health at all.