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Light Therapy

Light therapy (phototherapy) is given under the supervision of a physician. It is available in dermatologists’ offices, psoriasis day-care centers, phototherapy clinics, and some hospitals.


Ultraviolet B (UVB) light waves have wavelength’s ranging between 290-320 nm. It is the wavelength in sunlight which is responsible for most of the sunburns; sometimes tar, anthralin, calcipotriol/calcipotriene, or tazarotene topical therapy is also used in conjunction with UVB phototherapy. In 1925, Goeckerman used tar in addition to UVB, the Ingram method refers to tar baths, topical anthralin, and UVB.

UVB is given to the whole body in a cabinet, or to localized areas with a small portable unit. Most UVB given is broadband UVB. Narrow band UVB, which has 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 might be associated with aging of the skin, burning, and potentially an increase in skin cancer. UVB is usually administered three times a week for three months for clearing and maintenance can be achieved by using it less frequently. Long remissions may occur after UVB phototherapy.

The mechanism of action is unknown. It may reduce synthesis of DNA within epidermal cells and alter the immune response in the skin. It is less effective than PUVA but can be improved by adding other systemic therapies. The onset of response is slow.

Narrow Band UVB:

This is seen to be more effective than UVB. It can cause freckling and changes of skin aging. It takes longer to administer narrow band versus regular UVB.


PUVA stands for Psoralen (a medication that sensitizes your skin 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). After a set time after the psoralen has been taken or applied, the skin is exposed to ultraviolet A radiation in a cabinet 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 internal 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 to 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. Maintenance of improvement can in some be achieved by much less frequent use.

Phototherapy is useful when the psoriasis is generalized. It is effective and may have an ability to turn off the psoriasis for months. It can be used in combination with both methotrexate and the retinoids. The disadvantage is the increased risk of squamous cell carcinoma as well as melanoma. Photo damage with freckles and lentigines are seen particularly with PUVA.

The mechanism of action is unknown but involves the interaction of methoxsalen into DNA forming cross links. This results in the reduction of DNA synthesis and blocks cell proliferation. It may also suppress immune response in the skin.

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 (for example, Acitretin) and PUVA. The retinoid is usually started a couple of weeks before the PUVA. The total dose and number of PUVA treatments may be less if treatment with a retinoid is also given.


Laser light treatment has been used for localized resistant patches with some success. However, it is still considered experimental. The laser used is the 308nm Eximer® laser which gives a quick response. Since the light beam is relatively small, it is not a practical treatment option for generalized disease.