Closed mouth, also known as closed mouth pimples, is a mild form of acne. So many small dense closed mouth pimples on the chin may be related to increased androgen levels, proliferation of Propionibacterium acnes, and abnormal keratinization and hyperplasia of hair follicles and sebaceous gland ducts. 1. Increased androgen levels: androgens can promote sebaceous gland secretion, increase sebum secretion, and also promote the production of free fatty acids in skin cells. When the content of free fatty acids in sebum is elevated, the hair follicles and the ducts of the skin glands will be over-keratinized, resulting in clogged pores and obstacles to the discharge of sebum, leading to the formation of closed-cell acne. 2. Propionibacterium acnes multiplies: it can stimulate the ducts of hair follicles and sebaceous glands to undergo abnormal keratinization and hyperplasia, resulting in obstruction of sebum discharge and the formation of closed-cell pimples. 3. Abnormal keratinization and hyperplasia of hair follicles and sebaceous gland ducts: Abnormal keratinization and hyperplasia of hair follicles and sebaceous gland ducts can block pores, preventing sebum from being discharged and triggering closed-mouth pimples. It is recommended that people with a lot of dense small closed mouth acne on the chin go to the hospital in time, under the guidance of the doctor for standardized treatment, so as not to delay the condition.