Editing Humidity (section)

=== Human comfort ===
Although humidity is an important factor for thermal comfort, humans are more sensitive to variations in temperature than they are to changes in relative humidity.{{sfn|Fanger|1970|p=48}} Humidity has a small effect on thermal comfort outdoors when air temperatures are low, a slightly more pronounced effect at moderate air temperatures, and a much stronger influence at higher air temperatures.{{sfn|Bröde|Fiala|Błażejczyk|Holmér|2011|pp=481–494}}

Humans are sensitive to humid air because the human body uses evaporative cooling as the primary mechanism to regulate temperature. Under humid conditions, the ''rate'' at which perspiration evaporates on the skin is lower than it would be under arid conditions. Because humans perceive the rate of heat transfer from the body rather than temperature itself, we feel warmer when the relative humidity is high than when it is low.

Humans can be comfortable within a wide range of humidities depending on the temperature—from 30 to 70%{{sfn|Gilmore|1972|p=99}}—but ideally not above the Absolute (60&nbsp;°F Dew Point),<ref>[https://events.rdmobile.com/Sessions/Details/1098952] {{Webarchive|url=https://web.archive.org/web/20210210104307/https://events.rdmobile.com/Sessions/Details/1098952|date=2021-02-10}} ASHRAE Std 62.1-2019</ref> between 40%<ref name=infoplease.com /> and 60%.<ref name=engineeringtoolbox.com />  In general, higher temperatures will require lower humidities to achieve thermal comfort compared to lower temperatures, with all other factors held constant. For example, with clothing level = 1, metabolic rate = 1.1, and air speed 0.1&nbsp;m/s, a change in air temperature and mean radiant temperature from 20&nbsp;°C to 24&nbsp;°C would lower the maximum acceptable relative humidity from 100% to 65% to maintain thermal comfort conditions. The [[Center for the Built Environment|CBE]] Thermal Comfort Tool can be used to demonstrate the effect of relative humidity for specific thermal comfort conditions and it can be used to demonstrate compliance with ASHRAE Standard 55–2017.{{sfn|Schiavon|Hoyt|Piccioli|2013|pp=321–334}}

Some people experience difficulty breathing in humid environments. Some cases may possibly be related to respiratory conditions such as asthma, while others may be the product of anxiety. Affected people will often [[hyperventilation|hyperventilate]] in response, causing sensations of numbness, faintness, and loss of [[Attentional control|concentration]], among others.<ref>{{cite web|url=https://www.lung.ca/news/expert-opinions/pollution/heat-and-humidity|title=Heat and humidity – the lung association|website=www.lung.ca|date=26 August 2014|access-date=14 March 2018|archive-date=24 October 2020|archive-url=https://web.archive.org/web/20201024090754/https://www.lung.ca/news/expert-opinions/pollution/heat-and-humidity|url-status=live}}</ref>

Very low humidity can create discomfort, respiratory problems, and aggravate allergies in some individuals. Low humidity causes tissue lining nasal passages to dry, crack and become more susceptible to penetration of [[rhinovirus]] cold viruses.<ref name=rochester.edu /> Extremely low (below 20{{Spaces|1|thin}}%) relative humidities may also cause eye irritation.{{sfn|Arundel|Sterling|Biggin|Sterling|1986|pp=351–361}}<ref name=watertreatmentservices.co.uk /> The use of a [[humidifier]] in homes, especially bedrooms, can help with these symptoms.<ref name=webmd.com /> Indoor relative humidities kept above 30% reduce the likelihood of the occupant's nasal passages drying out, especially in winter.{{sfn|Arundel|Sterling|Biggin|Sterling|1986|pp=351–361}}<ref name=dhhs.nh.gov /><ref name=doh.wa.gov />

[[Air conditioning]] reduces discomfort by reducing not just temperature but humidity as well. Heating cold outdoor air can decrease relative humidity levels indoors to below 30%.<ref>{{cite web|title=Optimum Humidity Levels for Home|url=http://www.airbetter.org/optimum-humidity-levels-home/|website=AirBetter.org|date=3 August 2014|access-date=8 January 2017|archive-date=10 January 2020|archive-url=https://web.archive.org/web/20200110125649/https://www.airbetter.org/optimum-humidity-levels-home/|url-status=live}}</ref> According to [[ASHRAE 55|ASHRAE Standard 55-2017: Thermal Environmental Conditions for Human Occupancy]], indoor thermal comfort can be achieved through the [[PMV/PPD model|PMV]] method with relative humidities ranging from 0% to 100%, depending on the levels of the other factors contributing to thermal comfort.<ref name=ASHRAE55 /> However, the recommended range of indoor relative humidity in air conditioned buildings is generally 30–60%.{{sfn|Wolkoff|Kjaergaard|2007|pp=850–857}}<ref name=ASHRAE160 />