Genetics
Studies indicate that the most cases of Psoriasis may be inherited, due to the incidence of Psoriasis among the families of affected individuals. It is thought that certain inherited genes may be linked to Psoriasis, but the exact way this happens is not yet understood.
Infections
Infections are often involved in the development of psoriatic symptoms. Bacteria, particularly Streptococci, are the most commonly implicated pathogens, and are linked to Guttate Psoriasis. Human immunodeficiency virus (HIV) infection, although not a direct cause of Psoriasis, is known to increase the likelihood of developing more severe Psoriasis, if the person already has Psoriasis.
Stress
Psychological stress may worsen the condition, and, in some cases, may be enough to trigger it.
Medication
Some medications, particularly lithium, antimalarials and beta-blockers, have a negative effect on Psoriasis. Suddenly stopping therapy with strong topically applied or oral corticosteroids is likely to cause ‘rebound’ symptoms, which can be severe and may even result in erythroderma or even generalised pustular Psoriasis.