Medications
Drug-induced psoriasis may occur with beta blockers, lithium, antimalarial medications, nonsteroidal anti-inflammatory drugs, terbinafine, calcium channel blockers, captopril, glyburide, granulocyte colony-stimulating factor, interleukins, interferons, lipid-lowering medications,: 197  and paradoxically TNF inhibitors such as infliximab or adalimumab. Withdrawal of corticosteroids (topical steroid cream) can aggravate psoriasis due to the rebound effect. Pathophysiology
Psoriasis is characterized by an abnormally excessive and rapid growth of the epidermal layer of the skin. Abnormal production of skin cells (especially during wound repair) and an overabundance of skin cells result from the sequence of pathological events in psoriasis. The sequence of pathological events in psoriasis is thought to start with an initiation phase in which an event (skin trauma, infection, or drugs) leads to activation of the immune system and then the maintenance phase consisting of chronic progression of the disease. Skin cells are replaced every 3–5 days in psoriasis rather than the usual 28–30 days. These changes are believed to stem from the premature maturation of keratinocytes induced by an inflammatory cascade in the dermis involving dendritic cells, macrophages, and T cells (three subtypes of white blood cells). These immune cells move from the dermis to the epidermis and secrete inflammatory chemical signals (cytokines) such as interleukin-36γ, tumor necrosis factor-α, interleukin-1β, interleukin-6, and interleukin-22. These secreted inflammatory signals are believed to stimulate keratinocytes to proliferate. One hypothesis is that psoriasis involves a defect in regulatory T cells, and in the regulatory cytokine interleukin-10.
The risk for development of non-melanoma skin cancers is also increased. Psoriasis increases the risk of developing squamous cell carcinoma of the skin by 431% and increases the risk of basal cell carcinoma by 100%. There is no increased risk of melanoma associated with psoriasis. People with psoriasis have a higher risk of developing cancer. Epidemiology
Psoriasis is estimated to affect 2–4% of the population of the western world. The rate of psoriasis varies according to age, region and ethnicity; a combination of environmental and genetic factors is thought to be responsible for these differences. It can occur at any age, although it most commonly appears for the first time between the ages of 15 and 25 years. Approximately one third of people with psoriasis report being diagnosed before age 20. Psoriasis affects both sexes equally.Psoriasis affects about 6.7 million Americans and occurs more frequently in adults.Psoriasis is about five times more common in people of European descent than in people of Asian descent.People with inflammatory bowel disease such as Crohn disease or ulcerative colitis are at an increased risk of developing psoriasis. Psoriasis is more common in countries farther from the equator. Persons of white European ancestry are more likely to have psoriasis and the condition is relatively uncommon in African Americans and extremely uncommon in Native Americans. History
Scholars believe psoriasis to have been included among the various skin conditions called tzaraath (translated as leprosy) in the Hebrew Bible, a condition imposed as a punishment for slander.