Sebaceous Glands

The sebaceous glands produce a thick, creamy fluid – the sebum. The biggest sebaceous glands can be found in the face, the ears, the anal and genital region and down the middle of the back. Altogether, the skin has about 350,000 sebaceous glands. In the face, there are around 400 to 900 sebaceous glands per cm², in other regions fewer than 20 per cm². In most cases, the sebaceous glands occur together with the hairs and empty into the hair follicle.

The eyelids, the red part of the lips, the nipples, the small lips of the vagina, the glans (tip) of the penis and the clitoris are provided with “free” sebaceous glands, i.e. they open to the surface without any hairs. The sebaceous glands have a diameter of about 1 mm and are located in the dermis. They have many lobes or folds and consist of several individual glands with a common excretory duct. The sebum cells, like the cells of the epidermis, are produced continuously by stem cells at the base. As they mature, the sebum cells take in glycerine, free fatty acids, cholesterol and other lipid components. In terms of pH value, they are acidic. In the further course of development, the cells burst and the sebum, a mixture of lipids and dead sebum cells, is discharged. The time from formation to discharge of the sebum cells is 7 to 8 days.

The activity of the sebaceous glands is regulated by hormones and nerves. Androgens, progesterone and cortisone increase the production, oestrogens inhibit it. Sebum production is accelerated by heat and reduced by cold. The reduction in sebum production under the influence of cold temperatures is one reason for dry and rough skin in the cold seasons of the year.

The hormone dependency of the sebaceous glands can also be seen in infants, who have enlarged sebaceous glands immediately after birth. This is caused by the hormones circulating in the mother’s body. During childhood, the sebaceous glands are small and inactive and only develop in puberty under the influence of sex hormones at the age of 10 to 13. If sebum discharge is disturbed, the result are whiteheads (comedones) and blackheads, which are caused by oxidation of the sebum.