Closed mouth generally refers to closed pimples. There are many reasons for closed pimples on the eyebrow, which may be caused by endocrine factors, abnormal keratinization of follicular sebaceous gland ducts, and propagation of Propionibacterium acnes. 1. Endocrine factors: endocrine disorders, such as high levels of androgens in the body, will trigger an increase in sebaceous gland secretion, which may lead to the formation of closed pimples. 2. Abnormal keratinization of follicular sebaceous gland ducts: Abnormal keratinization of follicular sebaceous gland ducts usually causes the ducts to become smaller and blocked, which is not conducive to the normal discharge of shed cells and sebum, and may lead to the formation of closed pimples. 3. Propionibacterium acnes reproduction: Propionibacterium acnes can stimulate the proliferation and hyperkeratosis of keratinocytes at the follicular ducts, activating the inflammatory response, which may induce closed pimples. There are many causes of closed pimples on the brow, and patients are advised to seek medical examination to clarify the cause.