Editing Urbanization (section)

===Asthma===
Urbanization has also been associated with an increased risk of asthma as well. Throughout the world, as communities transition from rural to more urban societies, the number of people affected by asthma increases. The odds of reduced rates of hospitalization and death from asthmas has decreased for children and young adults in urbanized municipalities in Brazil. This finding indicates that urbanization may have a negative impact on population health particularly affecting people's susceptibility to asthma.<ref name=":1">{{Cite journal|last1=Ponte|first1=Eduardo Vieira|last2=Cruz|first2=Alvaro A.|last3=Athanazio|first3=Rodrigo|last4=Carvalho-Pinto|first4=Regina|last5=Fernandes|first5=Frederico L. A.|last6=Barreto|first6=Mauricio L.|last7=Stelmach|first7=Rafael|date=2018-02-01|title=Urbanization is associated with increased asthma morbidity and mortality in Brazil|journal=The Clinical Respiratory Journal|volume=12|issue=2|pages=410–417|doi=10.1111/crj.12530|pmid=27400674|s2cid=46804746|issn=1752-699X|url=https://www.arca.fiocruz.br/handle/icict/18781 }}</ref>

In low and middle income countries many factors contribute to the high numbers of people with asthma. Similar to areas in the United States with increasing urbanization, people living in growing cities in low income countries experience high exposure to air pollution, which increases the prevalence and severity of asthma among these populations.<ref>{{Cite journal|last1=Cruz|first1=Álvaro A.|last2=Stelmach|first2=Rafael|last3=Ponte|first3=Eduardo V.|date=2017-06-01|title=Asthma prevalence and severity in low-resource communities|journal=Current Opinion in Allergy and Clinical Immunology|language=en|volume=17|issue=3|pages=188–193|doi=10.1097/aci.0000000000000360|pmid=28333691|s2cid=6018699|issn=1528-4050}}</ref> Links have been found between exposure to traffic-related air pollution and allergic diseases.<ref name=":2">{{Cite journal|last1=Carlsten|first1=Christopher|last2=Rider|first2=Christopher F.|date=2017-04-01|title=Traffic-related air pollution and allergic disease|journal=Current Opinion in Allergy and Clinical Immunology|language=en|volume=17|issue=2|pages=85–89|doi=10.1097/aci.0000000000000351|pmid=28141628|s2cid=38066984|issn=1528-4050}}</ref> Children living in poor, urban areas in the United States now have an increased risk of morbidity due to asthma in comparison to other low-income children in the United States.<ref>{{Cite journal|last1=Keet|first1=Corinne A.|last2=Matsui|first2=Elizabeth C.|last3=McCormack|first3=Meredith C.|last4=Peng|first4=Roger D.|title=Urban residence, neighborhood poverty, race/ethnicity, and asthma morbidity among children on Medicaid|journal=Journal of Allergy and Clinical Immunology|volume=140|issue=3|pages=822–827|doi=10.1016/j.jaci.2017.01.036|pmid=28283418|date=September 2017|pmc=8050806|doi-access=free}}</ref> In addition, children with croup living in urban areas have higher hazard ratios for asthma than similar children living in rural areas. Researchers suggest that this difference in hazard ratios is due to the higher levels of air pollution and exposure to environmental allergens found in urban areas.<ref>{{Cite journal|last1=Lin|first1=Sheng-Chieh|last2=Lin|first2=Hui-Wen|last3=Chiang|first3=Bor-Luen|date=2017-09-01|title=Association of croup with asthma in children|journal=Medicine|language=en|volume=96|issue=35|pages=e7667|doi=10.1097/md.0000000000007667|pmid=28858086|pmc=5585480|issn=0025-7974}}</ref>

Exposure to elevated levels of ambient air pollutants such as nitrogen dioxide (NO<sub>2</sub>), carbon monoxide (CO), and particulate matter with a diameter of less than 2.5 micrometres (PM<sub>2.5</sub>), can cause DNA methylation of CpG sites in immune cells, which increases children's risk of developing asthma. Studies have shown a positive correlation between ''Foxp3'' methylation and children's exposure to NO<sub>2</sub>, CO, and PM<sub>2.5</sub>. Furthermore, any amount of exposure to high levels of air pollution have shown long term effects on the ''Foxp3'' region.<ref>{{Cite journal|last1=Prunicki|first1=Mary|last2=Stell|first2=Laurel|last3=Dinakarpandian|first3=Deendayal|last4=de Planell-Saguer|first4=Mariangels|last5=Lucas|first5=Richard W.|last6=Hammond|first6=S. Katharine|author-link6=S Katharine Hammond|last7=Balmes|first7=John R.|last8=Zhou|first8=Xiaoying|last9=Paglino|first9=Tara|date=2018-01-05|title=Exposure to NO2, CO, and PM2.5 is linked to regional DNA methylation differences in asthma|journal=Clinical Epigenetics|volume=10|pages=2|doi=10.1186/s13148-017-0433-4|pmid=29317916|pmc=5756438|issn=1868-7083 |doi-access=free }}</ref>

Despite the increase in access to health services that usually accompanies urbanization, the rise in population density negatively affects air quality ultimately mitigating the positive value of health resources as more children and young adults develop asthma due to high pollution rates.<ref name=":1" /> However, urban planning, as well as emission control, can lessen the effects of traffic-related air pollution on allergic diseases such as asthma.<ref name=":2" />