Closed mouth acne, or whitehead acne, may be caused by increased sebum secretion, keratinization of follicular sebaceous gland ducts, and propagation of Propionibacterium acnes. 1. Increased sebum secretion: due to the rise in androgen levels during puberty, sebaceous glands produce a large amount of sebum, which can induce whiteheads. In addition, prolonged late night, high-fat diet can also induce sebum secretion, resulting in the appearance of closed mouth acne. 2. Keratinization of follicular sebaceous gland ducts: when the follicular opening of the body is over-keratinized, narrowed and blocked, it can lead to sebum stagnation, inducing the formation of acne. 3. Propionibacterium acnes reproduction: when the hair follicle is blocked, it will cause Propionibacterium acnes to reproduce in large numbers and produce free fatty acids, leading to inflammatory damage of acne. It is recommended that patients with whiteheads and acne should consult a doctor to find out the cause of their acne and receive standardized treatment under a doctor’s guidance.