Editing Ultraviolet (section)

====Sunscreen safety debate====
{{Main|Sunscreen}}

[[File:UV and Vis Sunscreen.jpg|thumb|left|Demonstration of the effect of sunscreen. The left image is a regular photograph of his face; the right image is of reflected UV light. The man's face has sunscreen on his right side only. It appears darker because the sunscreen absorbs the UV light.]]

Medical organizations recommend that patients protect themselves from UV radiation by using [[sunscreen]]. Five sunscreen ingredients have been shown to protect mice against skin tumors. However, [[Potential health risks of sunscreen|some sunscreen chemicals]] produce potentially harmful substances if they are illuminated while in contact with living cells.<ref name=Parsons>{{cite journal |author1=Xu, C. |author2=Green, Adele |author3=Parisi, Alfio |author4=Parsons, Peter G |year= 2001 |title= Photosensitization of the sunscreen octyl p‑dimethylaminobenzoate&nbsp;b UV‑A in human melanocytes but not in keratinocytes |journal= Photochemistry and Photobiology |volume= 73 |issue= 6 |pages=600–604 |doi=10.1562/0031-8655(2001)073<0600:POTSOP>2.0.CO;2 |pmid=11421064|s2cid=38706861 }}</ref><ref name=Knowland1993>{{cite journal |author1=Knowland, John |author2=McKenzie, Edward A. |author3=McHugh, Peter J. |author4=Cridland, Nigel A. |title= Sunlight-induced mutagenicity of a common sunscreen ingredient | journal= FEBS Letters |volume= 324 |pages=309–313 |year=1993 |pmid=8405372 |doi= 10.1016/0014-5793(93)80141-G | issue=3|bibcode=1993FEBSL.324..309K |s2cid=23853321 }}</ref> The amount of sunscreen that penetrates into the lower layers of the skin may be large enough to cause damage.<ref>{{cite journal | last1 = Chatelaine | first1 = E. | last2 = Gabard | first2 = B. | last3 = Surber | first3 = C. | year = 2003 | title = Skin penetration and sun protection factor of five UV filters: Effect of the vehicle | url = http://www.karger.com/Article/FullText/68291 | journal = Skin Pharmacol. Appl. Skin Physiol | volume = 16 | issue = 1 | pages = 28–35 | doi = 10.1159/000068291 | pmid = 12566826 | s2cid = 13458955 | access-date = 26 December 2013 | archive-date = 27 December 2013 | archive-url = https://web.archive.org/web/20131227063745/http://www.karger.com/Article/FullText/68291 | url-status = live | url-access = subscription }}</ref>

Sunscreen reduces the direct DNA damage that causes sunburn, by blocking UVB, and the usual [[Sun Protection Factor|SPF rating]] indicates how effectively this radiation is blocked. SPF is, therefore, also called UVB-PF, for "UVB protection factor".<ref>{{cite journal |pmid=21283919 |volume=10 |issue=2 |title=The impact of natural sunlight exposure on the UV‑B – sun protection factor (UVB-SPF) and UVA protection factor (UVA-PF) of a UV‑A / UV‑B SPF&nbsp;50 sunscreen |date=February 2011 |journal=J. Drugs Dermatol. |pages=150–155 |vauthors=Stephens TJ, Herndon JH, Colón LE, Gottschalk RW }}</ref> This rating, however, offers no data about important protection against UVA,<ref>{{cite journal |pmid=21669263 |doi=10.1016/j.ijpharm.2011.05.071 |volume=415 |issue=1–2 |title=Sunscreen products: what do they protect us from? |date=August 2011 |journal=Int. J. Pharm. |pages=181–184 |vauthors=Couteau C, Couteau O, Alami-El Boury S, Coiffard LJ }}</ref> which does not primarily cause sunburn but is still harmful, since it causes indirect DNA damage and is also considered carcinogenic. Several studies suggest that the absence of UVA filters may be the cause of the higher incidence of melanoma found in sunscreen users compared to non-users.<ref name=Garland>{{cite journal |vauthors=Garland C, Garland F, Gorham E |title=Could sunscreens increase melanoma risk? |journal=Am. J. Public Health |volume=82 |issue=4 |pages=614–615 |year=1992 |pmid=1546792 |doi=10.2105/AJPH.82.4.614 |pmc=1694089}}</ref><ref name=Westerdahl2000>{{cite journal |vauthors=Westerdahl J, Ingvar C, Masback A, Olsson H |title= Sunscreen use and malignant melanoma | journal= International Journal of Cancer |volume=87 |issue=1 |pages=145–150 |year=2000 |pmid=10861466 |doi=10.1002/1097-0215(20000701)87:1<145::AID-IJC22>3.0.CO;2-3 |doi-access= }}</ref><ref name=Autier>{{cite journal |vauthors=Autier P, Dore JF, Schifflers E |title=Melanoma and use of sunscreens: An EORTC case control study in Germany, Belgium and France |journal=Int. J. Cancer |volume=61 |issue= 6|pages=749–755 |year=1995| doi = 10.1002/ijc.2910610602 |pmid=7790106|s2cid=34941555 |display-authors=etal}}</ref><ref name="Weinstock">{{cite journal |author=Weinstock |first=M. A. |year=1999 |title=Do sunscreens increase or decrease melanoma risk: An epidemiologic evaluation |url=https://www.jidsponline.org/action/showPdf?pii=S1087-0024%2815%2930243-4 |url-status=live |journal=Journal of Investigative Dermatology Symposium Proceedings |volume=4 |issue=1 |pages=97–100 |doi=<!-- Deny Citation Bot--> |pmid=10537017 |archive-url=https://web.archive.org/web/20221205021844/https://www.jidsponline.org/action/showPdf?pii=S1087-0024(15)30243-4 |archive-date=5 December 2022 |access-date=5 December 2022}}</ref><ref name=Vainio>{{cite journal |author1=Vainio, H. |author2=Bianchini, F. |title=Commentary: Cancer-preventive effects of sunscreens are uncertain |journal= Scandinavian Journal of Work, Environment & Health |volume=26 |issue=6 |pages=529–531 |year=2000 |doi=10.5271/sjweh.578 |doi-access=free}}</ref> Some sunscreen lotions contain [[titanium dioxide]], [[zinc oxide]], and [[avobenzone]], which help protect against UVA rays.

The photochemical properties of melanin make it an excellent [[photoprotection|photoprotectant]]. However, sunscreen chemicals cannot dissipate the energy of the excited state as efficiently as melanin and therefore, if sunscreen ingredients penetrate into the lower layers of the skin, the amount of [[reactive oxygen species]] may be increased.<ref name="Hanson">{{cite journal |author1=Hanson, Kerry M. |author2=Gratton, Enrico |author3=Bardeen, Christopher J. |title=Sunscreen enhancement of UV-induced reactive oxygen species in the skin |doi=10.1016/j.freeradbiomed.2006.06.011 |journal=Free Radical Biology and Medicine |volume=41 |issue=8 |pages=1205–1212 |year=2006 |pmid=17015167 |s2cid=13999532 |url=https://escholarship.org/content/qt9f14s2dd/qt9f14s2dd.pdf?t=oe9hj9 |access-date=6 September 2018 |archive-date=14 March 2020 |archive-url=https://web.archive.org/web/20200314065450/https://escholarship.org/content/qt9f14s2dd/qt9f14s2dd.pdf?t=oe9hj9 |url-status=live }}</ref><ref name=Parsons/><ref name=Knowland1993 /><ref name=Damiani1999>{{cite journal |author1=Damiani, E. |author2=Greci, L. |author3=Parsons, R. |author4=Knowland, J. |title=Nitroxide radicals protect DNA from damage when illuminated in vitro in the presence of dibenzoylmethane and a common sunscreen ingredient |journal= Free Radic. Biol. Med. |volume=26 |issue=7–8 |pages=809–816 |year=1999 |doi=10.1016/S0891-5849(98)00292-5 |pmid=10232823}}</ref> The amount of sunscreen that penetrates through the [[stratum corneum]] may or may not be large enough to cause damage.

In an experiment by Hanson ''et al''. that was published in 2006, the amount of harmful [[reactive oxygen species]] (ROS) was measured in untreated and in sunscreen treated skin. In the first 20&nbsp;minutes, the film of sunscreen had a protective effect and the number of ROS species was smaller. After 60&nbsp;minutes, however, the amount of absorbed sunscreen was so high that the amount of ROS was higher in the sunscreen-treated skin than in the untreated skin.<ref name="Hanson"/> The study indicates that sunscreen must be reapplied within 2&nbsp;hours in order to prevent UV light from penetrating to sunscreen-infused live skin cells.<ref name="Hanson"/>