When skin cells are produced too fast

My dermatologist says that I have psoriasis. What causes it?

Psoriasis is a common skin condition, which affects about 2 to 3 per cent of the world’s population. We believe there is a genetic component in development of the condition, though it can be triggered by environmental conditions like stress and depression. Certain medications can also trigger psoriasis for example beta blockers (used in treating high blood pressure and angina), lithium and some anti-malarial drugs. Under normal circumstances, it takes 28 days for skin cells to shed. However, in psoriasis, the skin cells shed too quickly - around seven days. This happens because the immune system malfunctions and begins to attack itself by targeting skin cells. The immune system is normally supposed to defend us and fight infections caused by bacteria and viruses.