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What Is Phototherapy?

Phototherapy is the use of light waves as a treatment. The American Academy of Dermatology recommends that phototherapy be used to treat atopic dermatitis (AD) as a second-line therapy, meaning that it is only used after the primary recommended treatment hasn’t worked to clear AD. In the treatment of AD, primary treatment is the use of emollients (moisturizers), topical steroids, and topical calcineurin inhibitors. Phototherapy may also be used as a maintenance therapy or in conjunction with topical treatments for people with chronic AD.1

Forms of light therapy

Various forms of ultraviolet (UV) light are used in phototherapy for AD. UV light is on the spectrum between visible light and x-rays with a wavelength between 400 and 10 nanometers. It is not visible to the human eye due to its shorter wavelength and higher frequency than what the brain can perceive as images. Also referred to as UV radiation, UV light is present in sunlight as well as in artificial forms, such as those used in phototherapy for AD.2,3

UVA light is between 320-400 nm and is the least harmful. It is frequently referred to as “black light,” and it is commonly used to cause objects to glow in the dark. UVA can cause immediate skin darkening. UVB light is 280-320 nm and causes delayed skin tanning and sunburns with prolonged exposure. UVB light increases the risk of skin cancer and other cellular damage.2

There are multiple forms of light therapy that have been proven to be of benefit treating AD, including:

  • Natural sunlight
  • Narrowband UVB (NB UVB), which uses wavelengths of 311-313 nm
  • Broadband UVB (BB-UVB), which uses wavelengths of 280-320 nm
  • UVA
  • Topical and systemic psoralen plus UVA (PUVA) – psoralen is a substance that makes the skin more sensitive to the UVA light
  • UVA and UVB (also called UVAB)
  • Goeckerman therapy, which combines coal tar plus UVB1,4

There have been limited trials comparing the different forms of light therapy to each other, so no definitive recommendation for any one form exists. However, natural sunlight is likely less effective than artificial light sources, which are more targeted. UVA phototherapy and UVB phototherapy have increased risks of side effects, and UVAB has limited availability. The most commonly recommended light therapy for people with AD is NB-UVB, due to its low risk of side effects, effectiveness, and availability in most areas.1

Dosing and frequency of phototherapy

The frequency of phototherapy sessions and the dosage of light vary for individual patients, based on their skin type and the phototherapy equipment being used. Phototherapy may be used on a scheduled basis, on an intermittent basis, or more continuously for maintenance therapy. The monitoring of phototherapy by a qualified physician is important to provide the benefits of light therapy and minimizing the potential risks or side effects. Doctors can also take into account an individual patient’s history of skin cancer and medications that may increase a person’s sensitivity to light.1

Phototherapy may be used by itself (as monotherapy) or in combination with other treatments, like emollients and topical steroids. Using light therapy may decrease the need for topical steroids and topical immunomodulators. Using topical calcineurin inhibitors with phototherapy is generally not recommended.1

Side effects of phototherapy

The incidence of side effects experienced with phototherapy that is monitored by a physician is low, however, patients considering phototherapy should be cautioned to the potential of side effects. Side effects from phototherapy may include local redness and tenderness, itching, burning, stinging, and actinic damage, which changes the appearance of the skin, causing fibrous, red spots or visible, spidery blood vessels.

Rarely, phototherapy may cause side effects such as nonmelanoma skin cancer, melanoma (particularly with the use of PUVA), brown patches on the skin (lentigines), rash, inflammation of the hair follicles (folliculitis), separation of the nail from the nail bed (photo-onycholysis), a reactivation of herpes simplex virus (HSV), and an abnormal amount of facial hair (facial hypertrichosis). UVA therapy can cause the formation of cataracts, and the addition of oral psoralen to UVA therapy frequently causes side effects such as headaches, nausea, and vomiting. Oral psoralen also increases an individual’s sensitivity to light, which can affect both their skin and their eyes, for several hours after ingestion.1

Written by Emily Downward | Reviewed October 2019
  1. Sidbury R, et al. Guidelines of care for the management of atopic dermatitis. J Am Acad Dermatol. 2014;71:327-49.
  2. Stanford Solar Center. Accessed online on 5/2/17 at
  3. He W, Zhu F, Ma X, Zhao X, Zheng M, Chen Z, et al. (2011) Actinic Skin Damage and Mortality - the First National Health and Nutrition Examination Survey Epidemiologic Follow-up Study. PLoS ONE .6(5): e19907.
  4. Berneburg M, Röcken M, Benedix F. Phototherapy with narrowband vs broadband UVB. Acta Derm Venereol. 2005;85(2):98-108. doi: 10.1080/00015550510025579