Skin Cell Physiology
The skin is a complex organ made up of many layers of flat cells called epithelial cells. At the bottom of the layers of skin cells are germ cells, which are the cells that make new epithelial cells. This means the youngest skin cells are at the bottom of the skin layers, and the oldest ones rise to the surface of the skin (and are exposed to the outside world). This is important because the cells on the surface of the skin experience a lot of damage and have to be constantly replaced. These germ cells allow skin to constantly renew and replenish itself.
Psoriasis and the Immune System
Psoriasis is caused by a problem with the immune system. Normally, the immune system is designed to only attack cells that come from outside the body. However, sometimes the immune system becomes abnormally activated so that it attacks some of the body's own healthy cells as if they were pathogenic. This is called an auto-immune disease. One kind of cell that is often involved in auto-immune diseases is the T-cell, which is responsible for circulating throughout the body and attacking foreign material. In the case of psoriasis, T-cells are released into the bloodstream that get activated by the germ cells that make new skin cells. When this happens, they release a number of chemicals (called cytokines) that are used to cause inflammation.
Inflammation and Psoriasis
Instead of being killed by the T-cells and the resulting inflammation, the skin germ cells get stimulated. This makes them divide more rapidly, causing more epithelial cells to be formed. This causes a rapid push of new skin cells to the surface. The result is inflamed skin (which is why one common symptom of psoriasis is red patches of skin), combined with rapid skin cell proliferation (causing the development of "scales" made up of skin cells). Because psoriasis is caused by problems with the immune system, it's usually treated with anti-inflammatory medications such as corticosteroids, which work to suppress the immune system.
