Why do we still have allergies?
Why are there still allergies after all the evolution we have been through? Why haven't we overcome this problem?
In fact, the trend with allergies may be the opposite as to what you might expect with evolution. It could be that humans are actually getting increasingly likely to develop allergies. The leading explanation in the scientific community to explain this is called the 'Hygiene Hypothesis'.
Think back to your great-great-great-grandparents. Chances are that they lived on a farm, grew up playing outside, and had a lot of siblings. If you think in microbiological terms, your great-great-great-grandparents probably encountered a LOT of bacteria and viruses and parasites and all sorts of other things. They would have been exposed to hay and grass, to unprocessed animal products, to stuff in the dirt in the fields they might have played in. This would have given their early immune systems quite a lot of training in regards to what it should respond to, and how much it should respond. In the field of immunology, it is thought that this early, hearty training of the immune system can leave a kid with a nice balanced immune system, which is equally developed in its ability to respond to all different kinds of threats. If you want to learn more about the training of the immune system, I talked about it in further detail in this blog article.
So, let's fast forward to now. Think about your little cousin, or next-door-neighbour, or future child that lives in a city. Perhaps in a sparkling clean apartment, with no siblings, and it either is or is perceived to be too dangerous to play outside. This child probably won't encounter very many parasites, unprocessed animal products, or hay. In some ways this is an excellent thing: this child is unlikely to get the terrible diseases that were rampant in the times of our great-great-great-grandparents. For instance, you don't hear about kids contracting cowpox very often these days. But in such a clean environment, it is thought that the parts of the immune system that protect you against things like parasites, for instance, are less developed and nuanced. In essence, the immune system is less balanced.
The main message here is that keeping a human healthy is a very complicated task for the immune system. It must recognize and react to "foreign" (not from our own body) invaders, but not too excessively. An allergic reaction is basically the immune system reacting to a poke in the eye with a declaration of war. The hygiene hypothesis suggests that the immune system might react this way because it's never had a poke in the eye before, and doesn't know that it's not a deadly attack. This is of course a simplification, but the details of how allergies work is a whole other can of worms that I won't get into today.
In practical terms, what does this mean? I am definitely not suggesting that you should be giving your kid unpasteurized milk and honey or exposing him or her to nasty parasites. But, I am suggesting that playing outside is a good thing, visiting petting zoos can be a healthy activity, and that the ten-second-rule might not be such a bad idea after all.
Until next week, enjoy your peck of dirt!