Editing Ultraviolet (section)

===Beneficial effects===

UV (specifically, UVB) causes the body to produce [[vitamin D]],<ref>{{Cite journal |last1=Wacker |first1=Matthias |last2=Holick |first2=Michael F. |date=2013-01-01 |title=Sunlight and Vitamin D |journal=Dermato-endocrinology |volume=5 |issue=1 |pages=51–108 |doi=10.4161/derm.24494 |issn=1938-1972 |pmc=3897598 |pmid=24494042}}</ref> which is essential for life. Humans need some UV radiation to maintain adequate vitamin&nbsp;D levels. According to the World Health Organization:<ref name="who.int"/>
<blockquote>There is no doubt that a little sunlight is good for you! But 5–15&nbsp;minutes of casual sun exposure of hands, face and arms two to three times a week during the summer months is sufficient to keep your vitamin D levels high.</blockquote>

Vitamin D can also be obtained from food and supplementation.<ref>{{cite journal |last1=Lamberg-Allardt |first1=Christel |title=Vitamin&nbsp;D in foods and as supplements |journal=Progress in Biophysics and Molecular Biology |date=1 September 2006 |volume=92 |issue=1 |pages=33–38 |doi=10.1016/j.pbiomolbio.2006.02.017 |pmid=16618499 |language=en |issn=0079-6107 |doi-access=free }}</ref> Excess sun exposure produces harmful effects, however.<ref name="who.int">{{cite report |url=https://www.who.int/uv/faq/uvhealtfac/en/index1.html |title=The known health effects of UV: Ultraviolet radiation and the INTERSUN Programme |archive-url=https://web.archive.org/web/20161016090300/http://www.who.int/uv/faq/uvhealtfac/en/index1.html |archive-date=16 October 2016 |publisher=World Health Organization}}</ref>

Vitamin D promotes the creation of [[serotonin]]. The production of serotonin is in direct proportion to the degree of bright sunlight the body receives.<ref>{{cite magazine |author=Korb, Alex |date=17 November 2011 |title=Boosting your serotonin activity |magazine=Psychology Today |url=https://www.psychologytoday.com/blog/prefrontal-nudity/201111/boosting-your-serotonin-activity |archive-url=https://archive.today/20170801135657/https://www.psychologytoday.com/blog/prefrontal-nudity/201111/boosting-your-serotonin-activity |archive-date=1 August 2017}}</ref> Serotonin is thought to provide sensations of happiness, well-being and serenity to human beings.<ref>{{cite journal |last = Young |first = S.N. |year = 2007 |title = How to increase serotonin in the human brain without drugs |journal = Journal of Psychiatry and Neuroscience |volume = 32 |issue = 6 |pages = 394–399 |pmid = 18043762 |pmc = 2077351}}</ref>

====Skin conditions====
UV rays also treat certain skin conditions. Modern phototherapy has been used to successfully treat [[psoriasis]], [[eczema]], [[jaundice]], [[vitiligo]], [[atopic dermatitis]], and localized [[scleroderma]].<ref>{{cite journal |last1=Juzeniene |first1=Asta |last2=Moan |first2=Johan |title=Beneficial effects of UV radiation other than via vitamin&nbsp;D production |journal=Dermato-Endocrinology|date=27 October 2014 |volume=4 |issue=2 |pages=109–117 |doi=10.4161/derm.20013 |pmid=22928066 |pmc=3427189}}</ref><ref>[http://healthycanadians.gc.ca/healthy-living-vie-saine/environment-environnement/sun-soleil/effects-uv-effets-eng.php "Health effects of ultraviolet radiation"] {{webarchive|url=https://web.archive.org/web/20161008013441/http://healthycanadians.gc.ca/healthy-living-vie-saine/environment-environnement/sun-soleil/effects-uv-effets-eng.php |date=8 October 2016 }}. Government of Canada.</ref> In addition, UV radiation, in particular UVB radiation, has been shown to induce [[cell cycle]] arrest in [[keratinocytes]], the most common type of skin cell.<ref>{{Cite journal |last1=Herzinger |first1=T. |last2=Funk |first2=J.O. |last3=Hillmer |first3=K. |last4=Eick |first4=D. |last5=Wolf |first5=D.A. |last6=Kind |first6=P. |year=1995 |title=Ultraviolet&nbsp;B irradiation-induced G2 cell cycle arrest in human keratinocytes by inhibitory phosphorylation of the cdc2 cell cycle kinase |journal=Oncogene |volume=11 |issue=10 |pages=2151–2156 |pmid=7478536}}</ref> As such, sunlight therapy can be a candidate for treatment of conditions such as psoriasis and [[exfoliative cheilitis]], conditions in which skin cells divide more rapidly than usual or necessary.<ref>{{cite journal |last1=Bhatia |first1=Bhavnit K. |last2=Bahr |first2=Brooks A. |last3=Murase |first3=Jenny E. |year=2015 |title=Excimer laser therapy and narrowband ultraviolet&nbsp;B therapy for exfoliative cheilitis |journal=International Journal of Women's Dermatology |volume=1 |issue=2 |pages=95–98 |doi=10.1016/j.ijwd.2015.01.006 |pmid=28491966 |pmc=5418752}}</ref>