Final answer:
The hygiene hypothesis suggests that cleaner living conditions in developed countries have led to an underactive immune system that, lacking real pathogens to combat, causes allergies and autoimmune diseases by reacting to harmless substances. Initially proposed by David Strachan, the hypothesis correlates the rise in allergies with the decline in infectious diseases due to improved hygiene practices. Studies hint that some exposure to pathogens is essential for a well-functioning immune system.
Step-by-step explanation:
The Hygiene Hypothesis and Its Relationship to Immune-Related Conditions
The hygiene hypothesis is a theory that suggests an inverse relationship between the incidence of infectious diseases and the prevalence of autoimmune diseases, allergies, and asthma. It posits that the reduced exposure to pathogens in developed societies, due to improved hygiene and medical practices, may lead to an under-stimulated immune system. This under-stimulation may cause the immune system to overreact to harmless substances, resulting in allergic reactions and, potentially, autoimmune disorders.
According to the hypothesis, when the immune system lacks infectious agents to combat, it may inadvertently target the body's own tissues, leading to autoimmune diseases. The prevalence of allergies is increasing in developed countries, where people are living in cleaner environments compared to developing countries. Allergies involve an IgE antibody response to nonpathogenic substances such as pollen, food items, or pet dander, triggering symptoms like inflammation and histamine release. Moreover, the hypothesis was first introduced by David Strachan in 1989, observing that children in larger families, and thus exposed to more pathogens from siblings, had lower incidence of hay fever.
Researchers have linked good hygiene practices with the increased prevalence of immune disorders, suggesting that limited exposure to microbes during childhood could lead to a malfunctioning immune system later in life. This has been referred to as the 'eat dirt' theory, implying that some level of exposure to diverse antigens through less rigorous hygiene practices could be beneficial for the development of a robust immune response.