The exact cause of psoriasis is not fully known, but scientists believe an immune system problem combined with a genetic predisposition and environmental factors causes the skin condition. Mayo Clinic indicates that overactive T cells in the immune system attack healthy skin as if they were attempting to heal a wound or fight infection. New skin cells rise to the surface before older skin cells slough off, creating patchy skin.
The cause of this excessive T cell activity is not fully understood, but environmental factors may trigger psoriasis. According to Mayo Clinic, infections, injuries to the skin, bug bites, sunburn, stress, cold weather, smoking, heavy alcohol consumption and certain medications may trigger psoriasis. Medications that may exacerbate this condition include lithium, beta blockers, antimalarial drugs and iodides.
The National Psoriasis Foundation reveals that as many as 10 percent of the American population inherits one or more of the genes associated with psoriasis, yet only 2 to 3 percent of the general populace develops the disease. Scientists believe a genetic predisposition and exposure to triggers cause the immune response. Drugs such as Plaquenil, Quinacrine, chloroquine, hydroxychloroquine, Inderal, quinidine and indomethacin may cause a psoriasis response. Some of the benefits of these drugs outweigh the negative symptoms of psoriasis. Stress can cause the initial flare-up or aggravate already-existing psoriasis. Any type of infection that causes an immune response can trigger psoriasis symptoms. Injuries to the skin trigger a Koebner response. The University of Wisconsin-Madison explains a Koebner response causes lesions at the site of a skin injury.