allergicreaction

Severe allergic reaction, from Wikipedia

Allergies are frequently misunderstood, and that’s saying a lot since science doesn’t even fully understand them. But, what we do understand allows us to expose quackery and help steer our ship or knowledge towards the right answer.

We’ll start with an interesting correlation: children who have been vaccinized against tetanus have a higher chance of allergies later in life. The untrained eye would say “Aha! Obviously vaccines cause allergies,” but this would be making the classic mistake of confusing correlation with causation. The correlation can help us figure out the real culprit by leading us to ask “what was different among the vaccinated and unvaccinated populations beyond their vaccination status?”

The answer is hiding right under our noses: urban and more wealthy populations are more likely to be vaccinated than those living rurally. Mothers in an urban setting are more likely to feed their child with a bottle, and less likely to breast feed (due to social and logistical concerns). Children in an urban setting are less likely to be confronted with a vast range of “normal” contact with natural substances, and breathe in far more diesel (which can induce or intensify allergies).

Children living in the city are also less likely to come into contact with commensalist (also known as neutral) or even parastic creatures that have traditionally lived in us and helped modulate our immune system. That said, city and urban life contribute a lot of factors towards the development of allergies and is probably the likely explanation for why vaccination seems to correlate with allergies.

So given that our urban lifestyle appears to contribute to allergies (I will get into this in more detail later in the text), what potential do we have to detect them? Well, there are a lot of tests that are not effective, the Guardian names a few of the most popular and states:

…most internet and shop-bought allergy tests have no scientific basis. They include the York test, a home-testing kit that looks for specific IgG antibodies against food stuffs in the blood. While these antibodies are part of the immune system’s response to infections, “the best medical evidence has shown elevated IgG levels do not suggest an allergy”, the guide says. “Results are frequently positive in individuals who do not have an allergy or a food intolerance.”

Also debunked is the Vega test, a mixture of acupuncture and homeopathy, which attempts to measure electronic resistance across the skin while the child or adult holds the suspect food in their hand.

Hair follicle testing is also pointless, the guide says. “Hair is not involved in allergic reactions so testing hair samples cannot provide any useful information on allergic status.” Nor should people be deceived into thinking allergies are caused by an “energy blockage” which can be “diagnosed” by muscle testing and “cured” by acupuncture.

Parents can also make the mistake of trying to diagnose an allergy too early, and end up unnecessarily restricting a child’s diet. The following table displays when is the best time for testing for an allergy:

testingallergy

From Eigenmann, 2013 (http://onlinelibrary.wiley.com/doi/10.1111/pai.12066/full)

So, now that we’ve discussed properly identifying an allergy, you probably want to know what causes them. Well, as in everything in life, a certain predisposition makes about 40% people more likely to get an allergy (called atopy). This can be rooted in deficient T-regulator proteins, or a defective molecular switch (Fox3 transcription factor) for turning on their production.

But, as with nearsightedness, this predisposition always existed and yet the number of people with allergies continues to increase: what exactly about our lifestyle fosters allergies? The answer is a mix between an improved “hygiene hypothesis” combined with the newer “counter-regulation hypothesis.”

As mentioned above, city life is particularly conducive to allergy developement. Part of the reason appears to be, as Janesway’s Immunobiology explains “all types of infection might protect against the development of atopy by driving the production of cytokines such as IL-10 and transforming growth factor beta, which downregulate both TH1 and TH2 responses… decreased early exposre to common microbial pathogens and commensals in some way makes the body less efficient at producing regulatory T-cells, thus increasing the risk of making an allergic response to a common environmental antigen.

Combine this knowledge with the fact that diesel exhaust particles increase IgE (which, along with TH2, is the main driver of allergic reactions) production 20-50 fold when combined with a allergen, accompanying a shift towards TH2 cytokine production.

A further indication that our “sterilized” urban lifestyle is a driver of allergies is that therapy with helminthes worms (that have traditionally lived inside humans) can reduce the intensity of allergies and even bowel inflamation. Probiotics appear to help, as well.

Even within city populations children from families with three or more older siblings, and children aged less than 6 months who are exposed to other children -situations connected to increased exposure to infections- are somewhat protected against allergies, whereas children from smaller and more wealthy families were far more likely to have allergies.

So, what causes allergies? The answer is a mix between genetics, overly sterile lifestyle, and an evolutionary history where it carried an advantage to have slightly upregulated IgE levels with the expectation that a parasite or commensal would work from within to lower them. The take home message is to let children play outside, especially in nature, and not to worry too much about them getting dirty.

muddykid