Psoriasis is a lifelong disfiguring inflammatory skin disease, characterised by salmon-pink or red thickened skin plaques covered with silver-white scales. The rash usually takes a symmetrical distribution, is often itchy and may bleed. The aetiology and natural history of psoriasis remain elusive.
However, it is now regarded as an immune-mediated inflammatory disease (IMID), which involves T-cell activation and pro-inflammatory cytokine expression1. The global prevalence of psoriasis is around 2%, and its estimated prevalence was reported to be high in Asia (11.8 %) and almost entirely absent in the aboriginal population of South America.2
Psoriasis prevalence is influenced by age, sex and its phenotypes. There are several clinical phenotypes of psoriasis; however, plaque psoriasis (psoriasis vulgaris) is the most common phenotype and accounts for around 85%, followed by guttate psoriasis (more common in children than adults).1
Plaque psoriasis has a bimodal onset. Around 30% of adult psoriatic patients describe disease onset prior to the age of 16 years and in children the prevalence increases with age up to 18 years. In adults, psoriasis prevalence increases with age up to 35 years. Thereafter, prevalence does not vary significantly and usually declines after the age of 75 years. Plaque psoriasis affects adult males and females equally; in children females have an earlier onset age.1,2
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