The exact cause of psoriasis isn’t fully understood. It’s thought that overactive T cells, which are cells that fight off viruses and bacteria in your body, are involved. In people with psoriasis, T cells attack healthy skin cells and activate other immune responses. This increases the production of healthy skin cells, T cells, and other white blood cells.
As a result, too many skin cells accumulate on the skin’s outer layer. This is why some types of psoriasis cause the skin to have a scaly appearance. It normally takes weeks for new skin cells to form, but in people with psoriasis, skin cells form within days. The body doesn’t shed the excess cells and psoriasis lesions occur.
People with a compromised immune system, including those with HIV or those who get repeated infections, have a higher risk of getting psoriasis.