Hyperpigmentation may be caused by physiological reasons, such as long-term sun exposure; it may also be caused by pathological reasons, such as post-inflammatory hyperpigmentation. 1. Physiological causes: commonly found in sun exposure, after long-term sun exposure, the ultraviolet rays of the sun stimulate the proliferation of melanocytes to increase the synthesis of melanin particles, and also enhance the function of the transporter of melanosomes, thus making the skin tanned and the phenomenon of hyperpigmentation occurs. 2. Pathological reasons: post-inflammatory hyperpigmentation is a pigmentation increase disease caused by skin inflammation or injury. Common diseases that can cause post-inflammatory hyperpigmentation include acne, drug rash, and trauma. The condition may be the result of inflammatory substances stimulating melanocyte activation through a number of pathways, leading to an increase in the production of melanin granules, causing localized hyperpigmentation. There are many diseases or causes of hyperpigmentation, and patients are advised to go to the dermatology department of regular hospitals in time for a clear diagnosis and standardized treatment as prescribed by the doctor.