Category B - full version without watermark 1024x576 (check terms and conditions at The embed version with watermark is free of charge. - Description: Psoriasis is a common and benign skin disease of unknown origin. Different factors like infections, drugs or a genetic disposition trigger a misdirected attack of the immune system. This autoimmune reaction against the body's own horny cells in the epidermis leads to their rapid proliferation. The skin thickens in the affected areas and reddish, itchy and scaly lesions develop.