Monthly Archives: March 2008

Why are we getting more allergic : The Hygiene Hypothesis


 One of the tragedies of my life is that I am allergic to shellfish. I love the taste but I hate what happens to me after eating them. One day I was discussing my allergy with my sister who is a doctor and she asked me “Didn’t you notice that humans are getting  more and more allergies!”. I had never noticed that! It is true. I am allergic to shellfish. My grandfather who was a farmer in Punjab  was allergic to absolutely nothing( except some people!). And I noticed that my cousins who live in US have even more allergies than me. I know a kid who lives in England who is allergic to nuts, eggs and even wheat. That is bad! Are we humans getting more allergic? What could be causing this? Is it a side effect of economic development? In today’s VERITAS we will talk about a very interesting fact that my sister told me about allergies. It is called the Hygiene hypothesis- we are too clean for our own good.

    In the year 1989 David Strachan proposed the hygiene hypothesis. He was trying to understand why certain diseases like hay fever  or eczema are more common in families with 1-2 children and less common in large families. His proposal was that in large families  with lots of kids the children are exposed to more infectious diseases from one another and this makes them less prone to allergies.  He proposed that in smaller families children are not exposed to infections and thus develop more allergies. So he proposed a very  interesting relationship between infections and allergies- if you are exposed to more infections you will have less allergies as you grow older.

   This was a revolutionary proposal and doctors all around the world tested this. And most doctors found this relationship to be true. In some countries like Gambia in Africa more than 95% of the population have intestinal worms at some time of their lives.  But they have  NEVER heard of immune diseases(allergies) like Asthma, Crohn’s disease or multiple sclerosis. Doctors found that children who grew  up in farms which are not very clean almost never develop asthma. Doctors also noticed that children in developed countries have more allergies compared to children who live in developing countries.

  So there is definitely a relationship. But how does it work? The immune system is our defense against germs and other organisms like worms. It is not developed when we are born. It takes time to develop. During development it learns to recognize the enemies of our bodies. So if in childhood we get an infection our immune system learns to recognize the germs that carry that infection. It is  important that the immune system recognizes the disease causing agents because it may have to fight them repeatedly during  our life. But what happens if we do not get infections in childhood? What happens when in childhood we live in extremely clean environments?
What happens if in childhood we treat every infection with antibiotics? The immune system will not get a chance to recognize its real enemies. But the immune system has to do something! It turns its defenses against our own body or against harmless things around us. So when a child who has never seen an infection breathes flower pollen the immune system starts a fight against the harmless pollen to try and “kill” it causing more harm than good. That is an allergy. Similarly sometimes the  immune system thinks of the cells of our own body as enemies and starts fighting them. These are called auto-immune diseases. Some examples are diabetes type 1 and  rheumatoid arthritis.

Thus we see that it is very important for the immune system to know disease in order to develop properly. The immune system has to  be properly trained so that it can differentiate between the harmful germs and the harmless things around us and the useful cells within our own bodies. So do not deworm your children too often. Do not keep them extremely clean. Do not give them antibiotics whenever they  fall ill. Let their immune system be developed by infections and they will grow to healthy and allergy free adults. I really hope my kids are able to enjoy prawn curry without having their lips swollen- maybe for that I need to stop bothering about their coughs and colds.

       And speaking of the common cold, here is an excerpt from an Ogden Nash poem on the “common cold”. In this poem Nash feels bad when his doctor tells him that his problem is the common cold. Nash feels that his cold is special and not common.

                                                                       Go hang yourself, you old M.D,!
                                                                       You shall not sneer at me.
                                                                       Pick up your hat and stethoscope,
                                                                       Go wash your mouth with laundry soap;
                                                                       I contemplate a joy exquisite
                                                                       In not paying you for your visit.
                                                                       I did not call you to be told
                                                                       My malady is a common cold.

                                                                       Give ear, you scientific fossil!
                                                                       Here is the genuine Cold Colossal;
                                                                       The Cold of which researchers dream,
                                                                       The Perfect Cold, the Cold Supreme.
                                                                       This honored system humbly holds
                                                                       The Super-cold to end all colds;
                                                                       The Cold Crusading for Democracy;
                                                                       The Führer of the Streptococcracy.

       The complete poem is much longer and you can easily find it on the internet.



 Go, wondrous creature! mount where Science guides:
 Go, measure earth, weigh air, and state the tides:
 Instruct the planets in what orbs to run,
 Correct old time and regulate the Sun;

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Veritas by Kanwarpreet Grewal is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.