What is psoriasis? Psoriasis is an inflammatory skin condition which is not contagious. There are five different types of psoriasis, of which by far the most common is plaque psoriasis which is a form that is suffered by approximately 80% of psoriasis sufferers. This particular form of psoriasis (also known as ‘psoriasis vulgaris’, with the latter word meaning common) usually appears as reddish patches of raised skin which are often covered in a silvery-white scale.