How does acne actually form?

The occurrence of acne is influenced by a number of factors, so how does acne actually form?

The occurrence of acne is mainly related to excessive sebum production, blockage of sebaceous ducts, bacterial infection, and inflammatory reactions. The pathophysiological basis of acne is the rapid development of sebaceous glands and excessive sebum secretion, and the development of sebaceous glands is directly governed by androgens. After puberty, the level of androgens, especially testosterone, increases rapidly. Testosterone is converted to dihydrotestosterone in the skin by the action of 5-alpha reductase, which binds to androgen receptors in sebaceous cells. This increase in androgen levels promotes the development of sebaceous glands and the production of large amounts of sebum. Some patients with acne have higher blood levels of testosterone than those without acne. In addition, progesterone and dehydroepiandrosterone in the adrenal cortex also have a pro-sebum effect.

Sebum is mainly composed of keratins, wax esters, triacylglycerols, and small amounts of sterols and cholesterol esters. Abnormal keratinization of the follicular sebaceous ducts is another important factor. The formation of acne begins with the enlargement of the sebaceous follicle, which occurs secondary to abnormal keratinization of the keratinocytes. In the lower part of the follicular funnel, the lamellar granules of keratin-forming cells are reduced and replaced by a large number of tense filaments, bridging granules, and lipid inclusion bodies, which are not easily shed.

The secretion and drainage of large amounts of sebum can easily lead to bacterial infections. Various microorganisms such as Propionibacterium acnes, Staphylococcus albicans and Malassezia are present in the hair follicles, with Propionibacterium acnes infection being the most important. Propionibacterium acnes is an anaerobic bacterium, and the obstruction of sebum excretion creates a good local anaerobic environment for it to proliferate. The lipase produced by Propionibacterium acnes can break down triacylglycerols in sebum to produce free fatty acids, which is the main factor leading to inflammatory damage in acne.

In addition, P. acnes can also produce peptides that chemotactic neutrophils, activate complement and cause leukocytes to release various enzymes, which can induce or aggravate inflammation. In addition to the above factors, the occurrence of acne in some patients is also related to the immune function of the body, especially in some specific types of acne such as acne conglobata and acne fulminans, where the immune response plays an important role.