Hygiene Hypothesis Explained
The hygiene hypothesis is one possible hypothesis that attempts to explain the increase in autoimmune diseases (such as asthma and allergies) in modern industrialized society.
Wikipedia defines the hygiene hypothesis as ...
"the hygiene hypothesis is a hypothesis that states that a lack of early childhood exposure to infectious agents, symbiotic microorganisms (e.g., gut flora or probiotics), and parasites increases susceptibility to allergic diseases by suppressing natural development of the immune system"
Autoimmune disease has tripled in the last few decades and affect roughly 24 million Americans.
MSNBC.com reports in 2010 that allergies of all types (including food allergies) are on the rise in developed countries including the United States.
In 2011, National Public Radio website blog says that asthma in the United States is up 7.7% from what it was in 2005.
Asthma and allergies are autoimmune type conditions where the body is attacking its own cells due to the fact that the immune system in not able to precisely distinguish "friend" or "foe" agents.
MedPedia says that "Allergy and autoimmune disorders result when the immune system overreacts or reacts inappropriately." Paper on PubMed.gov says that "Allergy and autoimmunity result from dysregulation of the immune system."
What is the Hygiene Hypothesis
The hygiene hypothesis is defined as follows in a paper by Becker ...
"The hygiene hypothesis is a widely held theory of the etiology of asthma and atopic disorders which builds on observations of rural versus urban distribution of disease. It suggests that cleaner environmental conditions in westernized countries, as compared to developing countries, play a role in the increase of the prevalence of these disorders in western countries"
The hygiene hypothesis suggests that when children develop in overly sanitized environment, their immune system do not grow strong enough. Just like muscles have to be stressed a little to make it stronger, so does the immune system.
In the late 1990s, Dr. Erika Von Mutius found that the rates of allergies and asthma in the children of more polluted East Germany was less than the more sanitized modern West Germany.
Another study looked at the rates of exercise-induced bronchospams in children in Ghana. Think of exercise-induced brochospams as asthama that is induced by exercise. They found that the rates in 2003 (when the country had developed social-economically) were higher than the rates in 1993 -- almost doubled the rates.
A paper from the Academy of Science, Paris France says ...
"Western countries are being confronted with a disturbing increase in the incidence of most immune disorders, including autoimmune and allergic diseases. Converging epidemiological evidence indicates that this increase is linked to improvement of the socio-economic level of these countries. Epidemiological and clinical data support the hygiene hypothesis according to which the decrease of infections observed over the last three decades is the main cause of the incessant increase in immune disorders."
Dr. Mark Hyman also mentions that in developing countries where hygiene is poor and infections common there is very little allergy and autoimmunity. This is referenced on page 188 of his book The UltraMind Solution where he also writes ...
"We are becoming hypersensitive to our environments, perhaps because we live in an oversterilized environment and our immune systems don't mature properly. Or because we are eating hybridized and genetically modified (GMO) foods full of antibiotics, hormones, pesticides, and additives that were unknown to our immune systems just a generation or two ago."
So there he provides two possible explanations to our bodies over-sensitivity to our environments. One is the hygiene hypotheses and the other is the prevalence of pesticides and additives, etc.
Other Autoimmune Disease
Celiac disease is another autoimmune disease where the body's immune system attacks its own tissues (in this case the small intestines).
In the book Celiac Disease, Peter Green cites a study that the rate of celiac disease is much higher (1 in 107) in cleaner more modernized Finland than in Russia where the rates were less (1 in 496 occurrence). Since the genetic predisposition to celiac disease and the wheat consumption were about the same in both countries, some suggest that the difference is due to the environment.
Green writes that the hygiene hypothesis ...
"proposes that an exposure to infections and unhygienic conditions early in life somehow conveys protection against the development of allergies."
No one is definitively saying that a clean environment is the cause of allergies and asthma either. The hygiene hypothesis is just that -- a hypothesis. It only "suggests a possibility". It does not prove.
Many people do not believe in the hygiene hypothesis (me included). Paul Jaminet is also not a strong believer in it as mentioned on Chris Kresser podcast.
Of course, we do not want to go back to pre-modern times when bad bacteria kills many people. We do still want to continue to use vaccines and anti-bacteria soap.
But perhaps we need not be overly concerned with children playing in the dirt.
-  Allergies mysteriously on rise in U.S. - Health - msnbc.com
-  Asthma On The Rise: NPR
Federal health officials estimate nearly 1 in 12 Americans, or 25 million people have the respiratory disorder. Asthma prevalence is up a little in recent years, but severe attacks have held pretty steady.
-  Asthma as a paradigm for autoimmune disease. [Int Arch Allergy Immunol. 2003] - PubMed result
-  Allergy and Autoimmune Disorders - Medpedia
-  Why is the incidence of autoimmune diseases increasing in the modern world?
-  Exercise-Induced Bronchospasm and Atopy in Ghana: Two Surveys Ten Years Apart
-  Autism, asthma, inflammation, and the hygiene hypothesis
-  Autoimmune Disease: Stop Your Bodys Self-Attack
-  Is autism an autoimmune disease? [Autoimmun Rev. 2004] - PubMed result