Editing Asthma (section)

====Hygiene hypothesis====
The [[hygiene hypothesis]] attempts to explain the increased rates of asthma worldwide as a direct and unintended result of reduced exposure, during childhood, to non-pathogenic bacteria and viruses.<ref>{{cite journal | vauthors = Ramsey CD, Celedón JC | title = The hygiene hypothesis and asthma | journal = Current Opinion in Pulmonary Medicine | volume = 11 | issue = 1 | pages = 14–20 | date = January 2005 | pmid = 15591883 | doi = 10.1097/01.mcp.0000145791.13714.ae | s2cid = 44556390 }}</ref><ref>{{cite journal | vauthors = Bufford JD, Gern JE | title = The hygiene hypothesis revisited | journal = Immunology and Allergy Clinics of North America | volume = 25 | issue = 2 | pages = 247–62, v–vi | date = May 2005 | pmid = 15878454 | doi = 10.1016/j.iac.2005.03.005 }}</ref> It has been proposed that the reduced exposure to bacteria and viruses is due, in part, to increased cleanliness and decreased family size in modern societies.<ref name=Brook2013>{{cite journal | vauthors = Brooks C, Pearce N, Douwes J | title = The hygiene hypothesis in allergy and asthma: an update | journal = Current Opinion in Allergy and Clinical Immunology | volume = 13 | issue = 1 | pages = 70–7 | date = February 2013 | pmid = 23103806 | doi = 10.1097/ACI.0b013e32835ad0d2 | s2cid = 23664343 }}</ref> Exposure to bacterial [[endotoxin]] in early childhood may prevent the development of asthma, but exposure at an older age may provoke bronchoconstriction.<ref>{{cite journal | vauthors = Rao D, Phipatanakul W | title = Impact of environmental controls on childhood asthma | journal = Current Allergy and Asthma Reports | volume = 11 | issue = 5 | pages = 414–20 | date = October 2011 | pmid = 21710109 | pmc = 3166452 | doi = 10.1007/s11882-011-0206-7 }}</ref> Evidence supporting the hygiene hypothesis includes lower rates of asthma on farms and in households with pets.<ref name=Brook2013/>

Use of [[antibiotic]]s in early life has been linked to the development of asthma.<ref>{{cite journal | vauthors = Murk W, Risnes KR, Bracken MB | title = Prenatal or early-life exposure to antibiotics and risk of childhood asthma: a systematic review | journal = Pediatrics | volume = 127 | issue = 6 | pages = 1125–38 | date = June 2011 | pmid = 21606151 | doi = 10.1542/peds.2010-2092 | s2cid = 26098640 }}</ref> Also, delivery via [[caesarean section]] is associated with an increased risk (estimated at 20–80%) of asthma&nbsp;– this increased risk is attributed to the lack of healthy bacterial colonization that the newborn would have acquired from passage through the birth canal.<ref>{{harvnb|British Guideline|2009|p=72}}</ref><ref name="pmid21645799">{{cite journal | vauthors = Neu J, Rushing J | title = Cesarean versus vaginal delivery: long-term infant outcomes and the hygiene hypothesis | journal = Clinics in Perinatology | volume = 38 | issue = 2 | pages = 321–31 | date = June 2011 | pmid = 21645799 | pmc = 3110651 | doi = 10.1016/j.clp.2011.03.008 }}</ref> There is a link between asthma and the degree of affluence which may be related to the hygiene hypothesis as less affluent individuals often have more exposure to bacteria and viruses.<ref name="pmid14763924">{{cite journal | vauthors = Von Hertzen LC, Haahtela T | title = Asthma and atopy – the price of affluence? | journal = Allergy | volume = 59 | issue = 2 | pages = 124–37 | date = February 2004 | pmid = 14763924 | doi = 10.1046/j.1398-9995.2003.00433.x | s2cid = 34049674 | doi-access = free }}</ref>