In the summer, forehead acne always grows, in medical terms, it refers to common acne, the cause of which is still unclear, and may be related to the large secretion of sebum, sebaceous gland conduit keratinization, and the proliferation of Propionibacterium acnes and other factors. 1. Massive sebum secretion: Heredity and androgens can cause excessive sebum secretion in the body. In summer, hot weather can lead to a large amount of sebum secretion, which can lead to the appearance of acne vulgaris in summer, but the location is not specific. 2. Sebaceous gland duct keratinization: If the sebaceous gland ducts are keratinized, the follicle openings will become smaller and blocked, resulting in sebum not being able to be discharged out of the body, thus triggering acne vulgaris. 3. Proliferation of Propionibacterium acnes: Propionibacterium acnes produces hydrolytic enzymes and promotes keratinocytes, which may lead to acne vulgaris if it overpopulates. For patients with acne vulgaris on the forehead in summer, it is recommended to go to a regular hospital for examination to clarify the cause of the condition.