What is the Hygiene Hypothesis?

Mary McMahon

The hygiene hypothesis is a theory within the medical community which suggests that humans may actually be living lives which are too clean for their own good. The argument of the hygiene hypothesis is that early childhood exposure to things like bacteria, parasites, and so forth may teach the immune system to recognize these things, allowing it to focus on its original purpose, protecting the body from disease. Lack of such exposure may potentially be behind rising allergy rates in the developed world, according to the hygiene hypothesis.

The hygiene hypothesis says that people may develop allergies to pet dander and other substances because they have little exposure to harmful organisms.
The hygiene hypothesis says that people may develop allergies to pet dander and other substances because they have little exposure to harmful organisms.

This concept was originally proposed by a British researcher, David Strachan, in 1989. Strachan looked at the health of large families as opposed to small ones, and discovered that in families with many children, the children were often healthier and less prone to allergies. Strachan believed that this might be connected to increased exposure to things like bacteria which is common to large families, as it becomes difficult to control exposure to diseases when a large group of children is involved.

Some studies have found evidence to support the hygiene hypothesis.
Some studies have found evidence to support the hygiene hypothesis.

Researchers have also looked at other trends in modern human life which minimize exposure to harmful organisms, such as increased antibiotic use and the use of antimicrobial cleaning agents in the home. Some also believe that the development of things like airtight doors and windows has contributed to an accumulation of allergens in the home, by trapping these things indoors, rather than allowing them to circulate out.

The implication is that people who are exposed to potentially harmful organisms will develop an immune system which is capable of fighting such organisms, potentially making someone hardier. According to the hygiene hypothesis, when the immune system is not occupied with things like developing ways to fight parasites, it may learn to attack random foreign bodies like pollen, pet dander, and so forth. Essentially, by living “too cleanly,” people may be hampering the development of their immune systems.

Essentially, exposure to harmful things helps the immune system to regulate itself. It develops special cells known as t-cells which fight disease, and these cells learn to identify harmful substances only through exposure. Without being exposed to the myriad of organisms in the world which attack the human body, the immune system has no frame of reference, and instead it attacks things without any sort of checks or controls, potentially leading to various autoimmune diseases, among other things.

Several studies have been conducted on the hygiene hypothesis, and there is some evidence to support it. This does not mean that you should expose your children to a plethora of harmful bacteria and parasites, but it does mean that eating a little dirt might not necessarily be harmful. It may also be helpful to ease off on drugs like antibiotics, allowing the body to learn to fight mild infections on its own.

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Discussion Comments


This concept has been in Europe for more than 40 years and is common knowledge.


I think I am in agreement with this Hygiene

Hypothesis because I use to know that people who lived in a well polished environment that often get ill.


so true, because i come from lebanon originally and its obviously not a fully developed country. all my family and cousins and grandmas and grandpas so rarely have allergies, they barely have colds. i think it's precisely because of the hygiene hypothesis. when they where young they where in contact with all the microbes and all, therefore they are immune.

nice to now, great topic


Yeah, I heard a discussion about that on NPR not too long ago, and I forget exactly what it was called but there is this one bacteria that is absolutely un-killable! It was scary...it just feels better to not always surround yourself with all of those cleaning supplies...I always just use a hot rag to wipe down the counters :).


Several years ago it was put to me that disinfectants, anti-bacterial wipes etc were counterproductive in that they don't kill all the nasties: just the weakest ones. [You wouldn't have open heart surgery by a surgeon who only wiped their instruments with disinfectant.] Therefore rather than providing a healthier home these chemicals are in fact creating one populated by superbugs as a result of only the strongest bugs surviving to breed.

So, about 15 years ago, we gave up all disinfectants etc, and do our cleaning with simple detergent and water. Since then we've actually had better health. Other bonuses are that our home smells better [not chemical] and it even costs us less.

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