The sudden growth of extraordinarily large number of pimples on the forehead is usually referred to as acne, and the causes of its development are mainly related to the abnormal level of androgen secretion, the propagation of Propionibacterium acnes as well as heredity and other factors. 1. Endocrine changes: When the secretion of androgen increases in the body, it will cause the sebaceous glands to secrete more, thus inducing acne. 2. Propionibacterium acnes reproduction: A large amount of sebum secretion creates conditions for the growth of Propionibacterium acnes, which causes acne when it grows and reproduces in large quantities. 3. Genetic factors: People with similar diseases in their family will have a higher chance of developing acne again. Due to individual differences in clinical manifestations and a variety of causes, a doctor’s consultation is required for specific cases.