Normally, when a foreign invader, or antigen, infects the body, helper T-cells recognize the antigen as alien and trigger a series of immune responses to destroy it. In psoriasis, however, a process called autoimmunity probably occurs. The T-cells may mistake the body's proteins as foreign antigens and set off a series of events to rid the body of the perceived threat. Phagocytes are the other major white blood cells that are spurred into action by the overactive T-cells and are the primary factors in the destructive inflammatory response. As part of their activity, they produce cytokines, which are now believed to be critical players in the inflammatory process.
Cytokines attract to the scene large numbers of other phagocytes known as neutrophils.
Environmental Factors Weather . Cold dry weather is a common precipitant of psoriasis flares. Hot, damp, sunny weather helps relieve the problem in most patients. It should be noted, however, that some people have photosensitive psoriasis, which actually improves in winter and worsens in summer when exposed to sunlight. Stress, unexpressed anger, and emotional disorders, including depression and anxiety, are strongly associated with psoriasis flares.