Value Of Personal Hygiene: Excessive Hygiene May Lead To Serious Diseases?

After introduction of antibiotics in the 1940s, the number of infectious disease in the developed world went down sharply. People started to live longer and healthier. But a number of rather unexpected and unpleasant effects were also observed. One of them is a gradual and steady rise in autoimmune diseases and allergic reactions. Medical scientists and researchers do not have a clear explanation to this phenomenon at present time. Several interesting explanations were suggested, but none of them is proven beyond reasonable doubts by statistical and epidemiological data.

This hypothesis first came to light when David Strachan, in an article published in 2000, observed an inverse correlation between the occurrence of hay fever and the number of older siblings, after following more than 17 thousand children since they were born, back in 1958.

Family size, hygiene and infection diseases

Strachan’s hypothesis is centered on the possibility that, in smaller families, microbial exposure is limited, because the risk of infections spreading person to person is also smaller. However, Strachan also concedes that part of the reduction in infections in recent years is caused by improved hygiene standards, household conditions and general personal cleanliness. 

But how do exactly less infections equal more allergic conditions? As a matter of fact, there is some biologic basis for this hypothesis. Studies conducted with various types of bacteria and viruses show that infection with these microbial agents activates so-called TH1-mediated immune response, which down regulates another type of immune reactions called TH2-mediated responses. These TH2-mediated responses are the ones usually elicited in response to absolutely normal antigens (various chemicals and microbes in our environment) and which originate allergic conditions and allergies themselves.

This does support the hygiene hypothesis to some extent, as inadequate stimulation of the TH1 response might have led to overactive TH2 response, and consequently to a very sensitive antibody-mediated immunity. The net result of such combination of factors can be allergic disorders.  Nevertheless, this explanation does not stand on its own, because the rise in incidence of allergic diseases was accompanied by a rise in autoimmune diseases, which are mediated by TH1 responses of the immune system.

Lack of exposure to infectious agents equals weak immune system

An alternative explanation has thus arisen. Based on a series of experimental investigations, researchers have hypothesized that, since regulatory T cells of our immune system need to be stimulated by infectious agents (be them bacteria, viruses or parasites) in order to control TH-mediated responses, the absence of such stimulation would lead to poorly repressed TH1 and TH2 responses. A rise in autoimmune and allergic disorders follows from this theory. 

See Also: Bacteria And Viruses You Can Catch From Using Public Bathrooms

Besides immunologic explanations, the hygiene hypothesis is strongly supported by epidemiological data.

Statistics Seems To Support The Hygiene Hypothesis

Several epidemiological studies have investigated the protective effect of infectious agents in allergic and autoimmune diseases. The existence of one or more older siblings protects against development of hay fever and asthma, of multiple sclerosis and also of Type 1 Diabetes, as does attendance at day care during the first 6 months of life in the case of atopic dermatitis and asthma.

Interestingly, exposure to farming and cowsheds early in life prevents atopic diseases, especially if the mother is exposed during pregnancy.

However, these data have been contradicted by other studies showing an increased prevalence of asthma correlated with higher levels of endotoxins in urban housing. The level of endotoxins is higher in farms as compared to cities, and subjects are in contact with a greater variety of microbial compounds in farms, which could explain this discrepancy.

Genetics and other factors can play their role too

It is important, though, to not forget about the genetic factors. Recent studies have shown that an individual’s response to environmental and microbial exposures is partially dependent on his/her genetic make-up (usually referred to as genetic polymorphism in scientific literature). The genetic polymorphism is linked to the altered immune responses to various environmental stimuli. So while the influence of external factors is undeniable, it is impossible to ignore the important role of our genetic code in the development of immune system-related medical problems.

But despite the fact that several detailed reviews of studies of the hygiene hypothesis have been published in recent years, the studies have persistent limitations. Cross-sectional studies of this subject are intrinsically retrospective over very long periods of time and are therefore subject to a significant recall bias. In addition, lack of easy to get medical records can mask essential differences between subjects and controls – something which is quite likely to happen in the third world countries with limited budgets. Many of the factors studied are interrelated and impossible to separate properly.

So does excessive hygiene bring harm?

The hygiene hypothesis originated from epidemiological observations relating exposure to other children to a reduced risk of allergy. Studies are still in progress in a number of laboratories worldwide to try and explain this hypothesis.

See Also: Nine Ways Oral Hygiene Helps Keep Your Body and Mouth in Connection

Undeniable fact of life is that without some degree of exposure to the dangerous environmental elements our immune system simply cannot be trained to recognize them. At present, the medical science has not progressed far enough to make the immune system to recognize and eliminate any possible dangerous environmental elements from the body. As a result, some doctors would argue against the excessive cleanliness so often practiced by young mothers. However, we still need to see the solid undeniable evidences that such practice is harmful. In their absence, the hygiene hypothesis remains an interesting but still controversial point of view.