Last week I watched one of their best episodes in a while, Allergy Planet.
Yes, I assume you've guessed it's about allergies. In the last 50 years the number of people affected by allergies (and the types of allergies) has risen sharply, and it's getting even worse, being a really serious health problem.
Allergies are basically a failure of our immune system that starts to respond to harmless substances (allergens).
I had already learnt some years ago that one of the explanations for the increase in allergies is that in our "hyper clean" (wash your hands again and again, scrub the floor again and again...) developed societies, we get exposed to a very limited number of pathogens, so our immune system does not get enough training, and being unable to distinguish the "bad guys"(pathogens) from some of the harmless ones (most of the allergens), it starts unnecessary (and harmful) immune responses. Related to this, the documentary explains how the absence of gutworms seems to increase the likelihood of developing allergies. IgE, the antibody involved in most allergies, is also used to fight gutworms. Evolution provided humans (for which gutworms used to be a serious issue) with the ability to produce good amounts of IgE. Problem is that now, good part of the population is no longer affected by gutworms and this IgE, having lost his job (binding to these pathogens), decides to reemploy himself in binding to innocuous allergens (giving rise to allergic reactions). This is one more of the problems (the other one I can think of is Stress) caused by the fact that in the last centuries Natural Evolution has lagged behind the evolution of our societies.
All this reminds me of something I read somewhere some weeks ago, that guys born through cesarean could be missing contact with some bacteria that would play an important role in the development of their immune system (babies born in the "traditional way" get exposed to bacteria in mum's vagina that will help them to develop their immune system, well, there are some nuances here, in some cases he can get exposed to life threatening bacteria or viruses... biology is too complex...)
All this does not mean that "all dirt is good", as air pollution (that exposes us to many allergens) seems to be an important cause for allergies.
There's another case in which too much hygiene increases the likelihood for developing allergies, this time not for underexposure to pathogens, but for overexposure to allergens. Washing up our hands too often may lead to our skin barrier (an outer layer of our skin that protects us from external elements) getting damaged, allowing too many allergens to enter our body and making our Immune System go nuts.
So, to sum up, some level of exposure to pathogens is good for our Immune System to get trained, and low level of exposure to allergens helps us avoid allergies.
Other great BBC Horizon documentaries that I've watched in the last months:
- The Secret life of your body clock
- God on the Brain. Abut brain conditions that influence religious experiences. Here I learnt a new cool word, neurotheology.
- How to survive a disaster One of the most interesting things here is how our fear to ridiculous (for example, being the first one in raising the alarm when some smoke starts to get into the room) can lead us to total disaster.
- Not a BBC Horizon one, but given that I mentioned stress in one of the paragraphs above, this is a must addition to this list. Stress, portrait of a killer with the great Robert Sapolsky. This is the guy that time ago said in an interview in Redes this great sentence (I'm translating it from Spanish from my distant memories, so it's anything by literal): You can't be a biologist if you haven't repeated this sentence at least 1000 times: genes do not determine anything, they determine something under a specific environment
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