Two major immune system genes under investigation are interleukin-12 subunit beta ( IL12B ) on chromosome 5q , which expresses interleukin-12B; and IL23R on chromosome 1p, which expresses the interleukin-23 receptor, and is involved in T cell differentiation. Interleukin-23 receptor and IL12B have both been strongly linked with psoriasis.  T cells are involved in the inflammatory process that leads to psoriasis.  These genes are on the pathway that upregulate tumor necrosis factor-α and nuclear factor κB , two genes involved in inflammation.  Recently, the first gene directly linked to psoriasis has been identified. A rare mutation in the gene encoding for the CARD14 protein plus an environmental trigger was enough to cause plaque psoriasis (the most common form of psoriasis).  
PUVA is a special treatment using a photosensitizing drug and timed artificial-light exposure composed of wavelengths of ultraviolet light in the UVA spectrum. The photosensitizing drug in PUVA is called psoralen. Both the psoralen and the UVA light must be administered within one hour of each other for a response to occur. These treatments are usually given in a physician's office two to three times per week. Several weeks of PUVA is usually required before seeing significant results. The light exposure time is gradually increased during each subsequent treatment. Psoralens may be given orally as a pill or topically as a bath or lotion. After a short incubation period, the skin is exposed to a special wavelength of ultraviolet light called UVA. Patients using PUVA are generally sun sensitive and must avoid sun exposure for a period of time after PUVA. Common side effects with PUVA include burning, aging of the skin, increased brown spots called lentigines , and an increased risk of skin cancer , including melanoma . The relative increase in skin cancer risk with PUVA treatment is controversial. PUVA treatments need to be closely monitored by a physician and discontinued when a maximum number of treatments have been reached.
Erythrodermic psoriasis (sometimes called exfoliative psoriasis) – The most severe of the psoriasis types, erythrodermic psoriasis is usually found in people with unstable plaque psoriasis. It is known by the wide, fiery outbreak and is accompanied by severe itching and pain. During an outbreak of erythrodermic psoriasis, skin often comes off in “sheets.” Only about three percent of people with psoriasis have this type of psoriasis, and it requires immediate medical attention because it can cause increased heartrate and body temperature changes. Some cases, particularly if left untreated, can lead to protein and fluid loss, shivering episodes, pneumonia and even congestive heart failure.