Psoriasis is a chronic inflammatory skin disease. It is estimated that psoriasis affects at least 1 % of the population. Psoriasis appears as a rash on various parts of the skin. The rash in psoriasis can appear as small or large spots that are red and scaly. In addition, psoriasis has many different subtypes such as pustular (small pus-filled sterile pustules), inverse psoriasis (affecting areas such as groin and armpits), nail psoriasis, scalp psoriasis, and even life-threatening forms as such erythrodermic psoriasis. There is enormous variation in the way psoriasis presents. The large number of patients, each with their own set of unique circumstances, has required the development of a large variety of treatments for psoriasis. Indeed currently there is a multitude of treatment approaches.
One very effective treatment regimen for psoriasis involves the use of light.[1-3] It has been noticed for many years that sunlight has beneficial effects on psoriasis. Later on, it became clear that light in the ultraviolet B spectrum (UVB) is most beneficial. Finally, it was established that ultraviolet light in the narrow range of 311-313 nanometer (known as narrow band UVB or NB-UVB) is the safest yet most effective treatment regimen.[3-5]
How Does UV Light Work?
UV light works by various mechanisms and suppresses the immune system in the skin. This is a useful property when treating an inflammatory skin condition such as psoriasis. UVB specifically targets DNA and that may help to slow down psoriatic skin overgrowth. UVB changes the composition of inflammatory small molecules secreted by the skin cells, which reduces inflammation. UVB also activates molecules in the skin that help to ensure the health of skin cells and prevent the development of skin cancers, which is a serious concern when irradiating human skin with UV radiation (in practice, however, no evidence for increased cancer with NB-UVB treatments was found). Another form of light therapy for psoriasis involves the use of psoralens (medications that make the skin sensitive to light) followed by skin irradiation with ultraviolet A (UVA) light. This treatment is also known as psoralen based UVA treatment (PUVA).  The psoralen can be either ingested by mouth, applied as a cream or mixed into bath water (known sometimes as “soak PUVA”) PUVA works in similar ways to NB-UVB but has some limitations due to the toxicity of psoralens, their tendency to cause nausea and upset stomach and importantly the increased risk of skin cancers.
Use of light in the treatment of psoriasis has many advantages: a large area can be treated at each treatment session, and it is safe and painless. In a secondary way, light treatments may improve psoriasis just because the person is coming to the doctor’s office very frequently and is constantly reminded to treat their rash. However light therapy is not for everyone: a typical treatment regimen involves three weekly treatments for a few weeks, which can become very time-consuming (once the desired light dose is reached and control of disease is satisfactory the frequency of visits will decrease and sometimes “treatment vacations” are established). In addition, most lightboxes are very narrow and some people cannot tolerate being in a closed, narrow environment for prolonged periods of time. The more common side effect is a burn that is much like a sunburn if the dose is raised too quickly. Some healthcare providers may require a simple blood test (called antinuclear antibody or ANA) that may give a clue about a person’s sensitivity to UV radiation.
The use of UV light should be discussed with a qualified medical professional before starting any treatment plans. UV light should be used carefully since it can increase the risk for skin cancers and sunburns. Overall, NB-UVB is an effective and safe treatment for psoriasis and should be considered as part of the treatment regimen for many people with psoriasis.