牛皮癬, also known as 银屑病 or psoriasis, is a chronic skin condition characterized by red, scaly patches on the skin. It occurs when the immune system mistakenly accelerates skin cell production, leading to a buildup of cells on the surface. This can cause discomfort, itching, and sometimes pain. The exact cause of 牛皮癬 is not fully understood, but it is believed to involve genetic and environmental factors. Triggers can include stress, infections, and certain medications. While there is no cure, various treatments, such as topical therapies and 光疗, can help manage symptoms and improve quality of life.