It is a genetically determined condition that so often runs in families. The disease needs to be triggered to show itself on the skin.
Triggers can be injury to the skin, infections anywhere in the body and stress.
Triggers can occur at any age. It is unusual for young children to develop clinical psoriasis but young adults develop a form of psoriasis where lots of small spots of psoriasis - a form called guttate psoriasis. Plaque psoriasis occurs in men and women and can occur for the first time at any age. Psoriasis is now considered to be an immunological disease where the body is reacting to an as yet unidentified agent. The result is a change in the skin, where the skin cells, called keratinocytes, start to divide too quickly and mature too slowly.