L40-L45: Papulosquamous disorders

L40: Psoriasis

Psoriasis is a common, long-term skin condition that varies in severity from minor, localized patches to complete body coverage. It's primarily characterized by red, scaly patches on the skin, known as plaques, which are often itchy and sometimes painful. Psoriasis is a result of an overactive immune system, wherein new skin cells grow and move towards the skin surface faster than normal, thus not allowing the older cells to shed off, leading to the build-up of skin cells. It is not a contagious condition and cannot be transmitted through physical contact. While the exact cause of psoriasis is unknown, it is linked with several risk factors including genetics, environmental triggers like stress, skin injuries, and certain medication, amongst others. The condition typically presents in cycles, with periods of flare-ups alternating with times of remission. It generally affects the skin, but can also involve the joints, leading to psoriatic arthritis.