Hygiene hypothesis

In medicine, the hygiene hypothesis states that early childhood exposure to particular microorganisms (such as the gut flora and helminth parasites) protects against allergies by properly tuning the immune system.[1][2] In particular, a lack of such exposure is thought to lead to poor immune tolerance.[1] The time period for exposure begins before birth and ends at school age.[3]

While early versions of the hypothesis referred to microorganism exposure in general, later versions apply to a specific set of microbes that have co-evolved with humans.[1][4][2] The updates have been given various names, including the microbiome depletion hypothesis, the microflora hypothesis, and the "old friends" hypothesis.[4][5] There is a significant amount of evidence supporting the idea that lack of exposure to these microbes is linked to allergies or other conditions,[2][6][7] although it is still rejected by many scientists.[4][8][9]

The term "hygiene hypothesis" has been described as a misnomer because people incorrectly interpret it as referring to their own cleanliness.[1][8][10][11] Having worse personal hygiene, such as not washing hands before eating, only increases the risk of infection without affecting the risk of allergies or immune disorders.[1][4][9] Hygiene is essential for protecting vulnerable populations such as the elderly from infections, preventing the spread of antibiotic resistance, and combating emerging infectious diseases such as Ebola or COVID-19.[12] The hygiene hypothesis does not suggest that having more infections during childhood would be an overall benefit.[1][8]

  1. ^ a b c d e f Scudellari, Megan (2017). "News Feature: Cleaning up the hygiene hypothesis". Proceedings of the National Academy of Sciences. 114 (7): 1433–1436. Bibcode:2017PNAS..114.1433S. doi:10.1073/pnas.1700688114. PMC 5320962. PMID 28196925.
  2. ^ a b c Stiemsma, Leah; Reynolds, Lisa; Turvey, Stuart; Finlay, Brett (July 2015). "The hygiene hypothesis: Current perspectives and future therapies". ImmunoTargets and Therapy. 4: 143–157. doi:10.2147/ITT.S61528. PMC 4918254. PMID 27471720.
  3. ^ Roduit, Caroline; Frei, Remo; von Mutius, Erika; Lauener, Roger (2016). "The Hygiene Hypothesis". Environmental Influences on the Immune System. pp. 77–96. doi:10.1007/978-3-7091-1890-0_4. ISBN 978-3-7091-1888-7.
  4. ^ a b c d Alexandre-Silva, Gabriel M.; Brito-Souza, Pablo A.; Oliveira, Ana C.S.; Cerni, Felipe A.; Zottich, Umberto; Pucca, Manuela B. (December 2018). "The hygiene hypothesis at a glance: Early exposures, immune mechanism and novel therapies". Acta Tropica. 188: 16–26. doi:10.1016/j.actatropica.2018.08.032. PMID 30165069. S2CID 52131098.
  5. ^ "Reconstituting the depleted biome to prevent immune disorders". The Evolution and Medicine Review. 13 October 2010.
  6. ^ Cite error: The named reference Daley2014 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference VersiniJeandel2015 was invoked but never defined (see the help page).
  8. ^ a b c Björkstén, Bengt (2009). "The Hygiene Hypothesis: Do we still believe in it?". Microbial Host-Interaction: Tolerance versus allergy. Nestlé Nutrition Institute Workshop Series: Pediatric Program. Vol. 64. pp. 11–22. doi:10.1159/000235780. ISBN 978-3-8055-9167-6. PMID 19710512.
  9. ^ a b van Tilburg Bernardes, Erik; Arrieta, Marie-Claire (November 2017). "Hygiene Hypothesis in Asthma Development: Is Hygiene to Blame?". Archives of Medical Research. 48 (8): 717–726. doi:10.1016/j.arcmed.2017.11.009. PMID 29224909.
  10. ^ Wendel-Haga, M.; Celius, E.G. (November 2017). "Is the hygiene hypothesis relevant for the risk of multiple sclerosis?". Acta Neurologica Scandinavica. 136: 26–30. doi:10.1111/ane.12844. PMID 29068485.
  11. ^ Parker, W. (26 August 2014). "The 'hygiene hypothesis' for allergic disease is a misnomer". BMJ. 349 (aug26 2): g5267. doi:10.1136/bmj.g5267. PMID 25161287. S2CID 33624127.
  12. ^ Cite error: The named reference BloomfieldRook2016 was invoked but never defined (see the help page).