Acne occurs mainly on the face, which is why it is also known as “facial blisters”. “No matter what happens to the face, it is a matter of great concern. It is true that there are many other skin diseases on the face, but acne has attracted more attention because of its high incidence, elusive onset, and varying severity of lesions. So, where does acne come from? Now let’s slowly remove the layers of fog and see which streams have converged into the lake of acne.
Hair follicles and sebaceous glands and acne.
The source of water is the root of wood. It is certain that sebaceous glands and acne are closely related to each other.
We know that human skin is composed of epidermis, dermis and subcutaneous tissue. In the dermis, in addition to blood vessels, lymphatic vessels and nerves, there are many appendages that maintain the normal function of the skin, such as sweat glands, hair follicles, nails and sebaceous glands. Sweat glands secrete sweat, hair follicles are the cradle of hair growth, and sebaceous glands are the factories for sebum production.
1.The structure of sebaceous glands
The sebaceous gland is a lumpless gland surrounded by connective tissue and consists of a gland and a duct, which is closely related to the hair follicle because the duct opens at the follicle. The glands are sebaceous gland cells. As the cells continue to proliferate, differentiate and mature, their cytoplasm is filled with sebaceous droplets, forming secretory cells, and finally the gland cells disintegrate and are discharged together with the sebaceous droplets.
2.Distribution of sebaceous glands
The sebaceous glands are present in almost all parts of the body, except for the ventral surface of the palmoplantar and toes. It turns out that it is related to the type of sebaceous glands.
3. Follicular sebaceous gland types
Type I: Mainly located in the eyelashes, eyebrows, beard and head. It is a sebaceous gland that is accompanied by coarse hairs, where the glands are relatively small and the hairs
relatively long and higher than the skin surface.
Type II: sebaceous glands associated with fine hairs, with large gland volume and hairs protruding from the skin surface.
Type III: Follicular sebaceous gland with a large gland volume and almost no hair growth in the accompanying follicle. The hair follicle is sunken by the epidermis
The opening of the sebaceous gland meets the follicular duct, which is called the funnel of the follicle – when the duct of the sebaceous gland is hyperkeratotic in this part, sebum excretion is blocked. A hair follicle can have multiple sebaceous glands. This gland is located only on the face, chest and back. The frontal and cheek glands are the largest, and the back is also large. The more numerous ducts are filled with sebum and cellular debris and are a breeding ground for Propionibacterium acnes, the only gland that can form acne damage. The function of this gland is regulated by sex hormones. When androgen levels increase, its glands become larger and its secretory function is enhanced.
It can be seen that sebaceous glands and hair follicles are inextricably linked by nature: they are independent neighbors within the skin, but ultimately the same opening leads to the skin surface, so some people call this anatomical relationship the “follicular sebaceous unit”. The human face, back, and chest are the main distribution areas of the follicular sebaceous glands (type III sebaceous glands), with the two eyebrows to the sides of the nose and the perioral area to the jaw being the more abundant areas of these sebaceous glands. Therefore, it is easy to understand how acne can be interpreted as a chronic inflammatory skin disease of the sebaceous units of the hair follicles.
4. Function of the sebaceous glands
The function of the sebaceous glands is mainly to secrete sebum, which seems simple enough, but the sebum they secrete is extraordinary. When sebum is mixed with water and various substances discharged from sweat glands and stratum corneum to form an acidic sebum film, it inhibits the growth of bacteria and fungi. At the same time, sebum can moisturize hair and skin, and it is essential for a person to have a glowing appearance. Once sebum secretion is reduced, dryness and cracking of the skin or dryness and breakage of the hair can occur. Of course, when too much sebum is secreted, the pores will expand passively because too much sebum has to be excreted from the pores, making the face look pore-sized and greasy.
It is worth noting that there is a substance called triglyceride in the composition of sebum, which can be broken down to produce free fatty acids under the action of bacterial lipase in the hair follicles. This substance can cause inflammation in the sebaceous glands of hair follicles and plays an important role in the formation of acne.
5. Factors affecting the sebaceous glands
Under the influence of androgens, the sebaceous glands increase in size and become hyperactive in sebum secretion, producing thick and abundant sebum that cannot be excreted completely. On the other hand, the sebaceous gland of hair follicle itself has increased sensitivity to androgens, so that testosterone is transformed into more active dihydrotestosterone in the tissue by the action of 5-alpha reductase, which stimulates sebaceous gland cell turnover and lipid synthesis. In conclusion, under the action of androgens, the function of hair follicle sebaceous glands is enhanced, sebum secretion increases, the hair follicle opening is keratinized, and sebum excretion is impeded, providing a breeding ground for Acinetobacter, which is the basis for acne. Estrogen, on the other hand, is the opposite of androgen. Large amounts of adrenal corticosteroids can also enhance the function of the sebaceous glands and increase sebum excretion, so clinically, steroidal acne can occur after large amounts of corticosteroids are used. In addition, temperature and humidity also have an effect on the function of sebaceous glands. Generally, high temperature and high humidity can increase sebum excretion.