Hygiene hypothesis: A hypothesis that states that exposure to allergens in the environment early in life reduces the risk of developing allergies by boosting immune system activity. Conversely, relatively clean environment in early life would sway the immune system towards allergy -promoting responses. Also called the hygiene theory.
Full Answer
What is the hypothesis that a child's environment can be too clean?
The hygiene hypothesis says a child's environment can be "too clean," and the lack of exposure to germs does not give the immune system a chance to develop resistance to diseases. (Image credit: <a href="http://www.shutterstock.com/gallery-65904p1.html">Sebastian Kaulitzki</a>, <a href="http://www.shutterstock.com">Shutterstock</a>) ...
Who discovered that children in larger households have fewer instances of hay fever?
The hygiene hypothesis was first introduced in the late 1980s by David P. Strachan, a professor of epidemiology, in the British Medical Journal. Strachan found that children in larger households had fewer instances of hay fever because they are exposed to germs by older siblings. This finding led to further research that suggests a lack of early childhood exposure to less than pristine conditions can increase the individual's susceptibility to disease.
Why do babies have a weak immune system?
The idea is simple. When babies are inside the womb they have a very weak immune system because they are given protection by their mother's antibodies. When they exit the womb, though, the immune system must start working for itself.
Does a clean environment cause hay fever?
Research has indicated that children who are kept in very clean environments have a higher rate of hay fever, asthma and a wide range of other conditions. This is what is called the hygiene hypothesis.
What is the hygiene hypothesis?
The hygiene hypothesis proposes that exposure to microorganisms might alter the immune system such that allergi c diseases that are mediated by Th2 type responses no longer can develop. The immunological explanation of the hygiene hypothesis is rooted in the notion that a decrease in exposure to pathogens would weaken the Th1 type immune responses and therefore allow proallergic Th2 responses to become dominant. Helminth infections are a class of infectious agents that are highly prevalent in developing countries and currently affect more than two billion people worldwide in the same areas where the prevalence of allergies is low. As helminth infections induce a strong Th2 response, the immunological explanation of the hygiene hypothesis does not hold as in the same areas where Th2-inducing helminth infections are rampant, allergic disorders are seldom seen. There are currently two explanations for the inverse relationship between helminths and allergies despite both diseases being associated with Th2 responses. One is that chronic helminth infections are associated with strong regulatory responses which encompass regulatory T cells, regulatory B cells, alternatively activated macrophages, and tolerogenic dendritic cells and, therefore, can dampen inflammatory reactions. The other is that IgE responses that are induced in the presence of helminth infections are often to cross-reactive carbohydrate epitopes which have poor biological activity and therefore do not lead to allergic reactions. Insight into these two mechanisms can provide us with potential new treatments for allergic diseases using analogues of helminth-derived molecules.
How does hygiene affect the immune system?
The hygiene hypothesis associates the increase in the incidence of autoimmune diseases and allergy in developed countries with the effects of the environment on the immune system. It postulates that childhood infections educate the immune system on how to react to antigenic challenge. The immune system is a self-organizing system and like the brain it requires experience to learn how to behave [8 ]. However, as a consequence of improved hygiene, vaccination campaigns, and the use of antibiotics in industrialized countries, the “education” of the immune system has been significantly diminished, and the immune response runs out of control upon stimulation with otherwise innocuous substances.
Does hygiene increase allergies?
The hygiene hypothesis postulates that growing up in a more hygienic environment may increase the risk of developing allergies (Liu and Leung, 2006 ). This hypothesis has been prompted by the results of epidemiological studies showing that overcrowding and unhygienic conditions were associated with a lower prevalence of allergies, eczema and hay fever, and asthma. Infections and exposure to certain microbial agents early in life have been proposed as an explanation for these protective effects.
What is the Hygiene Hypothesis?
The "Hygiene Hypothesis" is a theory that suggests a young child's environment can be "too clean" to effectively stimulate or challenge the child's immune system to respond to various threats during the time a child's immune system is maturing.
Why is the hygiene hypothesis so difficult to prove?
Proving the hygiene hypothesis is difficult because of the complexity of the developing immune system, the difficulty in designing ethical studies in infants and young children, and getting control and experimental groups of children who have parents that would allow them to be involved in such studies. Like many hypotheses, aspects ...
When was the hygiene hypothesis proposed?
Although the term "Hygiene Hypothesis" was proposed in the late 1980's, many investigators trace its origins to earlier experiments with animals, mainly mice and rats born and raised in "germ-free" or sterile environments. When experimentally exposed to low doses of an infectious agent that would not harm normally raised rodents, ...
What is the hygiene hypothesis in autoimmunity?
The hygiene hypothesis in autoimmunity: the role of pathogens and commensals. The incidence of autoimmune diseases has been steadily rising. Concomitantly, the incidence of most infectious diseases has declined. This observation gave rise to the hygiene hypothesis, which postulates that a reduction in the frequency of infections contributes ...
Why are pathogens important?
Pathogens are known to be important, as autoimmune disease is prevented in various experimental models by infection with different bacteria, viruses and parasites. Gut commensal bacteria also play an important role: dysbiosis ...