Niels Finsen was the first physician to investigate the therapeutic effects of sunlight scientifically and to use sunlight in clinical practice. This became known as phototherapy. Sunlight contains many different wavelengths of light. It was during the early part of the 20th century that it was recognized that for psoriasis the therapeutic property of sunlight was due to the wavelengths classified as ultraviolet (UV) light. Ultraviolet wavelengths are subdivided into UVA (380–315 nm) UVB (315–280 nm), and UVC (< 280 nm). Ultraviolet B (UVB) (315–280 nm) is absorbed by the epidermis and has a beneficial effect on psoriasis.
Narrowband UVB (311 to 312 nm), is that part of the UVB spectrum that is most helpful for psoriasis. Exposure to UVB several times per week, over several weeks can help people attain a remission from psoriasis. Ultraviolet light treatment is frequently combined with topical (coal tar, calcipotriol) or systemic treatment (retinoids) as there is a synergy in their combination.
Ultraviolet B (UVB) light is more effective than UVA light for treating psoriasis, Exposure times start at 30 to 60 seconds and are gradually increased until light causes the skin to turn red. When the skin no longer turns red after this much exposure, the time is increased. Treatments are given daily or several times a week. UVB light is used alone, with tar products (Goeckerman treatment), or with anthralin applied to the skin (Ingram regimen). UVB light alone (without drugs) is used for widespread plaque psoriasis and guttate psoriasis..
Ultraviolet A (UVA) penetrates deeper into the skin than UVB Treatment with UVA typically takes 20 minutes for a session UVA light used with psoralen drugs is called PUVA. With PUVA, the treatment time is greatly reduced, from 20 minutes to about 2 minutes
Phototherapy may be given at locations such as a hospital or doctor's office, a psoriasis day care center, or your home (UVB). In general, your entire body is exposed to the light. (If psoriasis affects only certain areas of your body, UV light may be directed at these selected areas only.) You will wear sunglasses that block UV light and goggles or a blindfold to protect your eyes from getting cataracts. Men may also need to shield their genitals to protect them from an increased risk of genital cancer.
In other study reported that NB-UVB penetrates more deeply into the skin than broad-band UVB and is therefore highly effective for the treatment of psoriasis vulgaris. It is also less carcinogenic and has become popular as routine phototherapy in many countries around the world. Narrowband ultraviolet B (NB-UVB) irradiation is frequently the treatment of choice in mild to moderate cases of psoriasis vulgaris . Its therapeutic effects involve several mechanisms, including the induction of anti-inflammatory and immunosuppressive cytokines can effectively induce the apoptosis of T cell within corium and inhibit Langerhans cell’s antigen presentation and effect of activating T cell, can escape from DNA absorption peak (about 265mm) and consequently decrease carcinogenicity. Reported by Tzung et al, at the same radiation dose level, UVB may cause more serious DNA damage than NB-UVB; to achieve the same therapeutic effect, the radiant dose of NB-UVB is 10 times higher than UVB, but there is no significant difference of DNA damage caused by the two; in addition, erythema effect of NB-UVB is slighter than conventional UVB.
It is reported that the wave length most prone to cause erythema effect is about 300 nm, and discovered by the experiment on healthy volunteers that Joule amount for NB-UVB to cause the smallest erythema is 4 times of UVB, which indicate NB-UVB is less prone to cause erythema effect. Revealed by the study, the effective rate of NB-UVB radiation on psoriasis vulgaris is 83.7%, which is similar with the domestic and overseas reports, while the effective rate of UVB radiation on psoriasis vulgaris is only 37.9%, which indicates NB-UVB is with better therapeutic effect and fewer adverse effect than UVB, and NB-UVB radiation is one of the primary methods for treating psoriasis . NBUVB could be used in pregnancy, lactation and is a useful and well-tolerated treatment for children with severe or intractable cases, but concerns remain regarding its long term side effects.
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