Editing Psoriasis (section)

===UV phototherapy===
[[Phototherapy]] in the form of [[sunlight]] has long been used for psoriasis.<ref name=Lancet07/> UVB [[wavelength]]s of 311–313&nbsp;[[nanometer]]s are most common. [[UV-B lamps]] have been developed for this treatment.<ref name=Lancet07/> The exposure time should be controlled to avoid overexposure and burning of the skin. The UVB lamps should have a timer that turns off the lamp when the time ends. The dose is increased in every treatment to let the skin get used to the light.<ref name=Lancet07/> Increased rates of cancer from treatment appear to be small.<ref name=Lancet07/> [[Narrowband UVB therapy]] has been demonstrated to have similar efficacy to [[psoralen and ultraviolet A phototherapy]] (PUVA).<ref name="Dogra2010"/> A 2013 meta-analysis found no difference in efficacy between NB-UVB and PUVA in the treatment of psoriasis, but NB-UVB is usually more convenient.<ref>{{cite journal | vauthors = Chen X, Yang M, Cheng Y, Liu GJ, Zhang M | title = Narrow-band ultraviolet B phototherapy versus broad-band ultraviolet B or psoralen-ultraviolet A photochemotherapy for psoriasis | journal = The Cochrane Database of Systematic Reviews | issue = 10 | pages = CD009481 | date = October 2013 | volume = 2016 | pmid = 24151011 | doi = 10.1002/14651858.CD009481.pub2 | pmc = 11076274 }}</ref>

<!-- Tanning bed benefits and limited effectiveness with UVA -->
One of the problems with clinical phototherapy is the difficulty many people have gaining access to a facility. [[Indoor tanning]] resources are almost ubiquitous today and could be considered as a means for people to get UV exposure when dermatologist-provided phototherapy is not available. Indoor tanning is already used by many people as a treatment for psoriasis; one indoor facility reported that 50% of its clients were using the center for psoriasis treatment; another reported 36% were doing the same thing. However, a concern with the use of commercial tanning is that tanning beds that primarily emit UVA might not effectively treat psoriasis. One study found that plaque psoriasis is responsive to [[erythema|erythemogenic]] doses of either UVA or UVB, as exposure to either can cause dissipation of psoriatic plaques. It does require more energy to reach erythemogenic dosing with UVA.<ref name="radack">{{cite journal | vauthors = Radack KP, Farhangian ME, Anderson KL, Feldman SR | title = A review of the use of tanning beds as a dermatological treatment | journal = Dermatology and Therapy | volume = 5 | issue = 1 | pages = 37–51 | date = March 2015 | pmid = 25735439 | pmc = 4374067 | doi = 10.1007/s13555-015-0071-8 }}</ref>

<!-- Risks of UV light therapy -->
UV light therapies all have risks; tanning beds are no exception, being listed by the [[World Health Organization]] as [[carcinogen]]s.<ref>{{cite book | vauthors=((World Health Organization)) | title=Artificial tanning devices: public health interventions to manage sunbeds | publisher=[[World Health Organization]] (WHO) | date=15 June 2017 | hdl=10665/255695 | isbn=978-92-4-151259-6 }}</ref> Exposure to UV light is known to increase the risks of melanoma and squamous cell and basal cell carcinomas; younger people with psoriasis, particularly those under age 35, are at increased risk from melanoma from UV light treatment. A review of studies recommends that people who are susceptible to skin cancers exercise caution when using UV light therapy as a treatment.<ref name="radack" />

A major mechanism of NB-UVB is the induction of [[DNA]] damage in the form of [[pyrimidine dimer]]s. This type of phototherapy is useful in the treatment of psoriasis because the formation of these dimers interferes with the [[cell cycle]] and stops it. The interruption of the cell cycle induced by NB-UVB opposes the characteristic rapid division of skin cells seen in psoriasis.<ref name="Dogra2010">{{cite journal | vauthors = Dogra S, De D | title = Narrowband ultraviolet B in the treatment of psoriasis: the journey so far! | journal = Indian Journal of Dermatology, Venereology and Leprology | volume = 76 | issue = 6 | pages = 652–61 | date = November–December 2010 | pmid = 21079308 | doi = 10.4103/0378-6323.72461 | doi-access = free | title-link = doi }}</ref> The activity of many types of immune cells found in the skin is also effectively suppressed by NB-UVB phototherapy treatments.<ref>{{cite journal | vauthors = Rácz E, Prens EP, Kurek D, Kant M, de Ridder D, Mourits S, Baerveldt EM, Ozgur Z, van IJcken WF, Laman JD, Staal FJ, van der Fits L | title = Effective treatment of psoriasis with narrow-band UVB phototherapy is linked to suppression of the IFN and Th17 pathways | journal = The Journal of Investigative Dermatology | volume = 131 | issue = 7 | pages = 1547–1558 | date = July 2011 | pmid = 21412260 | doi = 10.1038/jid.2011.53 | doi-access = free | title-link = doi | oclc = 6757253389 }}</ref> The most common short-term side effect of this form of phototherapy is redness of the skin; less common side effects of NB-UVB phototherapy are itching and [[blister]]ing of the treated skin, irritation of the eyes in the form of [[conjunctivitis|conjunctival inflammation]] or [[keratitis|inflammation of the cornea]], or [[Herpes labialis|cold sores]] due to reactivation of the [[herpes simplex virus]] in the skin surrounding the lips. Eye protection is usually given during phototherapy treatments.<ref name="Dogra2010"/>

PUVA combines the oral or topical administration of psoralen with exposure to ultraviolet A (UVA) light. The [[mechanism of action]] of PUVA is unknown but probably involves activation of psoralen by UVA light, which inhibits the abnormally rapid production of the cells in psoriatic skin. There are multiple mechanisms of action associated with PUVA, including effects on the skin's immune system. PUVA is associated with [[nausea]], [[headache]], [[Fatigue (physical)|fatigue]], burning, and itching. Long-term treatment is associated with [[squamous cell carcinoma]] (but not with [[melanoma]]).<ref name="Richard2013"/><ref name="Lapolla2011">{{cite journal | vauthors = Lapolla W, Yentzer BA, Bagel J, Halvorson CR, Feldman SR | title = A review of phototherapy protocols for psoriasis treatment | journal = Journal of the American Academy of Dermatology | volume = 64 | issue = 5 | pages = 936–49 | date = May 2011 | pmid = 21429620 | doi = 10.1016/j.jaad.2009.12.054 }}</ref> A combination therapy for moderate to severe psoriasis using PUVA plus [[acitretin]] resulted in benefit, but acitretin use has been associated with [[birth defect]]s and [[hepatotoxicity|liver damage]].<ref name="Dunn2011">{{cite journal | vauthors = Dunn LK, Gaar LR, Yentzer BA, O'Neill JL, Feldman SR | title = Acitretin in dermatology: a review | journal = Journal of Drugs in Dermatology | volume = 10 | issue = 7 | pages = 772–82 | date = July 2011 | pmid = 21720660 }}</ref>