In medicine, the<unk>  states that early childhood exposure to particular microorganisms (such as the gut flora and helminth parasites) protects against allergic diseases by contributing to the development of the immune system. In particular, a lack of exposure is thought to lead to defects in the establishment of immune tolerance. The time period for exposure begins in utero and ends at school age. While early versions of the<unk>  referred to exposure to microbes in general, updated versions apply to a specific set of microbial species that have co-evolved with humans. The updates have been given various names, including the microbiome depletion<unk> , the microflora<unk> , and the "old friends"<unk> . There is a significant amount of evidence supporting the idea that lack of exposure to these microbes is linked to allergies or other conditions, although scientific disagreement still exists. The term<unk> " has been described as a misnomer because people incorrectly interpret it as referring to personal cleanliness. Reducing personal<unk> , such as not washing hands before eating, is expected to simply increase the risk of infection without having any impact on allergies or immune disorders.<unk>  is essential for protecting vulnerable populations such as the elderly from infections, preventing the spread of antibiotic resistance, and for combating emerging infectious diseases such as Ebola or COVID-19. The<unk>  does not suggest that having more infections during childhood would be an overall benefit.
Hygiene hypothesis
Source control 
Bobath concept
Functional integration 
Chemical nomenclature
Terminology of alternative medicine
Organ trade
Recovery model