Psoriasis is a non-contagious skin disease which is characterized by large patches of red, itchy, scaly skin. The patches can range widely in size between patients from very small patches to those covering nearly the whole surface of the skin. However, the areas most commonly affected are the back of the forearms, the shins, the area around the navel, and the scalp. Symptoms are often worse in the winter, and can be made worse by beta blockers, NSAIDs, stress and infections. It affects about 2-4% of the population, and is equally likely in men and women across all age groups. It has been known since ancient times and Celcus was the first physician to describe it in writing. At the time, it was often confused with leprosy.
There are five different types of psoriasis, but by far the most common (making up 90% of total cases) is plaque psoriasis, which is characterized by white scales over red skin. Diagnosis is usually from visual examination, although a differential diagnosis must include diseases with a similar appearance. However, no invasive tests are required in most cases, although a biopsy may be performed.
The cause of the disease is not perfectly understood, but it is currently believed it is genetic in origin, but is triggered by environmental factors. It's etiology is better understood - excessive and rapid growth of the epidermal layer of the skin. Typically, skin cells in a normal individual are replaced about once a month. In a psoriasis patient, they are replaced every few days, particularly around wounds. The rapid growth is encouraged by an interaction of several cells in the immune system.
Treatment is focused on alleviating the symptoms. Steroids, Vitamin D3 ointments, ultraviolet light and immunosuppressants such as methotrexate are all used for this purpose. However, most types of generic lotions have no effect, and some moisturizing lotions can actually make the condition worse. Dietary changes can also be helpful. Fresh water fish appear to improve symptoms, while alcohol, red meat and dairy products can make them worse.
Although psoriasis is not dangerous, patients with the disease seem to have a higher incidence of several more serious conditions such as arthritis, lymphoma, cardiovascular disease, Crohn's disease and clinical depression. Patients who also have HIV usually suffer more severe symptoms.