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Light Therapy

Light therapy can be an effective modality to treat moderate psoriasis. It has long been recognized that regular, but brief exposure to ultraviolet (UV) light in a special standing light booth or to natural sunlight suppresses the immune system and reduces inflammatory responses by the body. Available UV light therapies include standard broad-band UVB phototherapy, narrow-band UVB and photochemotherapy (PUVA).

How the treatment works

  • UV radiation causes activated T cells in the psoriatic plaques to die. This method of controlled UV exposure acts to suppress inflammation-causing cells in the skin and slow down their excessive reproduction.
  • Light therapy is administered under the supervision of a physician.
  • Treatment facilities are available in select dermatologists' offices, psoriasis day-care centers, phototherapy clinics, and some hospitals.


  • Generally well-tolerated and very effective for moderate psoriasis
  • Non-invasive approach
  • Can be used in combination with drug therapies to improve treatment results
  • Relatively few and/or minor side-effects following short-term use
  • More cost effective than many systemic (oral) or biologic treatments


  • Therapy is time-consuming, due to the need for multiple treatment sessions that are required to gain control of the psoriasis, followed by less frequent maintenance therapy.
  • Side-effects include burning, darkened skin, skin irritation (redness and itching) and headaches.
  • UV light, especially PUVA (psoralen + UVA light), must be used conservatively because of the damage sustained by skin cells, which can lead to premature skin aging and increase the risk for skin cancer.
  • Treatment is not recommended for patients with a history of nonmelanoma skin cancer or melanoma.

Comments & Suggestions

  • Time commitment is required to attend multiple clinic visits in order to receive the prescribed treatments.
  • Treatment can be enhanced by gently removing scales by bathing prior to UV exposure.
  • Use of pre-treatment emollients with a thin consistency may improve results of UVB therapy.
  • Ongoing follow-up by a dermatologist is recommended for patients who have received prolonged exposure to light therapy, especially PUVA, to monitor for any signs of skin cancer.

UVB Phototherapy

Ultraviolet B (UVB) light waves have wavelength's ranging between 290-320 nm. It is the wavelength in sunlight that is responsible for most of the sunburns. Sometimes tar, anthralin, calcipotriol/calcipotriene, or tazarotene topical therapy can also be used in conjunction with UVB phototherapy. Common treatment regimens include the Goeckerman method, which uses tar in addition to UVB, and the Ingram method utilizes tar baths, topical anthralin and UVB.

UVB is given to the whole body in a chamber (size of a telephone booth), or to localized areas with a small portable unit. Most UVB given is broad-band UVB. Narrow-band UVB with a wavelength of 311 nm is available in certain centers. Some patients may do better with narrow-band UVB, but the risk of a sunburn reaction may be greater.

The eyes need to be protected with special glasses during UVB treatment in order to prevent eye damage. Although treatment is often limited to 2-4 weeks, long-term treatment may be associated with aging of the skin, burning and an increase risk for skin cancer. UVB is usually administered 3 times a week for 3 months for clearing, and maintenance can be achieved by using it less frequently. Long periods of remission may occur after UVB phototherapy.

The exact mechanism of action of UVB phototherapy is unknown, however, it is believed to reduce synthesis of DNA within epidermal cells and alter the immune response in the skin. UVB is less effective than PUVA, but its effectiveness can be improved by adding other systemic therapies. The onset of response is slow.

Narrow-band UVB

Narrow-band UVB (311 nm) is considered to be more effective than standard broad-band UVB (295-320 nm) therapy in treating plaque psoriasis. It can cause freckling and skin aging changes. Narrow-band UVB therapy takes longer to administer and the cost is higher in comparison to standard broad-band UVB.

PUVA (Photochemotherapy)

For more treatment resistant forms of psoriasis or when UVB fails, PUVA (psoralen + UVA light) may be prescribed. PUVA stands for psoralen (a medication that makes the skin more sensitive to ultraviolet A light waves) + UVA (ultraviolet A, with a wavelength range of 320-400 nm). The psoralen may be taken internally as a pill or applied to the skin (in bath water or as a cream, ointment or lotion). Following a set time, after the psoralen has been taken or applied, the skin is exposed to ultraviolet A radiation in a chamber or with a small portable unit.

You must wear protective eye glasses as soon as you take the psoralen pill during treatment (for both the oral and topical PUVA treatments), and for one day after your treatment, in order to prevent eye damage. Other potential side-effects include itching and dryness of the skin, a sunburn reaction, freckling, aging of the skin, and skin cancer. The pill often causes an upset stomach. You can minimize nausea by taking the psoralen pill with food. PUVA therapy is usually given initially 2-3 times a week, then less frequently as the skin improves. It takes about 25 treatments over a 2-3 month period before clearing takes place. Long remissions may occur after PUVA therapy. For some people, maintenance of the improvement can be achieved with much less frequent use.

The exact mechanism of action is unknown, but it likely involves methoxsalen (an example of psoralen) forming DNA crosslinks that result in cell destruction upon photoactivation. The treatment process reduces DNA synthesis and blocks cell proliferation. It is also believed to suppress immune responses in the skin.

Photochemotherapy is useful when the psoriasis is generalized. It is effective and may have an ability to clear the psoriasis for months. It can be used in combination with both methotrexate and retinoids. The disadvantage is the increased risk of squamous cell carcinoma, as well as melanoma. Signs of photodamage (such as freckles and lentigines) are particularly prevalent with PUVA.

The efficacy is very significant in a large percentage of patients. The duration of effect is long, but the onset of improvement is slow.


Re-PUVA refers to treatment with a retinoid (such as acitretin) and PUVA. The inclusion of a retinoid serves to enhance the effect of PUVA. This combination regimen is effective for the treatment of generalized and severe plaque psoriasis. Re-PUVA may be prescribed for patients who do not respond to UVB and PUVA treatments alone. In Re-PUVA, the number of PUVA treatments and the UVA dosage are reduced, in comparison to if a retinoid is not used. The retinoid is usually started a couple of weeks before the PUVA.

Laser Therapy

Laser light treatment has been used for localized resistant patches with some success, but it is still considered experimental. This advancement involves the use of a high energy excimer laser (308 nm) device that delivers a controlled beam of light to small areas of affected skin and produces a fairly quick response. This more targeted approach is able to provide higher doses of UVB directly to psoriatic plaques, which may result in fewer needed treatment sessions. However, since the light beam is relatively small, it is not a practical option for treating generalized disease. Potential side-effects include redness and blistering.