Who gets psoriasis?

Exact figures about the proportions of populations that have psoriasis do vary. However in Caucasian populations it is thought that around 2% have psoriasis. The incidence is less in Africans (0.7%), Asians and Native Americans (Camisa, 2004a). It affects men and women equally. The average age of onset is 30; however, psoriasis may be experienced for the first time much earlier than this or indeed much later. There do appear to be two peaks of onset, one in early adulthood and the other in later life (Williams, 1997).

There is little doubt that there is a genetic component to psoriasis; the earlier the psoriasis occurs and the more severe the disease, the stronger the familial association. However, monozygotic twins (i.e. those that come from one fertilised egg that divides) will not always both have psoriasis. This suggests that it is likely that environmental factors play a role in the development of active symptoms.

The understanding of the genetic components of psoriasis is constantly increasing as research allows ever more detailed examination of the human genome. There are a number of chromosomes (e.g. chromosome 6 and 17) which carry genes that seem to increase the likelihood of developing psoriasis, i.e. they are not causative genes but instead they increase the susceptibility of an individual to develop the condition. As there are a number of different genes which code for psoriasis, the way the psoriasis appears, when it appears and how it responds to treatment vary enormously.

Psoriasis, like all chronic skin conditions, is not contagious. This is important to stress to individuals when they are initially diagnosed with the condition as they may worry about passing the disease onto others.