The Oil Gland Of Skin And Its Associated Hair – final seat of development of acne

To know the basis acne formation requires understanding of two aspects of skin biology. First, keratinization and second, pilosebaceous unit.


The outermost layer of our skin is called epidermis, one of its major function is protection. The epidermis requires a tough material to handle the environmental hazards, that material is a protein called KERATIN. Keratin is an water insoluble, highly durable protein that provides structure to epidermis, hair and nails. An important quality of keratin is its ability to flex in multiple directions without tearing. The protective structures containing keratin form through a process called keratinization.

Epidermis has an average thickness of about 0.1 mm, and is made up of several layers of cells. Newly formed cells in the epidermis are slowly pushed to the surface. As the cells move from one epidermal layer to the next, they accumulate more and more keratin, through a process called keratinization. Eventually the keratinized cells (keratinocytes or corneocytes) slough off and are replaced by underlying cells that in turn become keratinized. This is a process where the most superficial layer is continuously shedding off (most of the dust in your bedroom is made of these tiny fragments of human skin) and new cells are continuously being added. Entire epidermis of 0.1 mm thickness may take about four to six weeks to completely replenish itself. So you produce a new epidermis every month.

Pilosebaceous unit

Sebaceous glands are microscopic exocrine glands in the skin that secrete an oily or waxy matter, called sebum. The sebaceous glands are found throughout all areas of the skin except the palms of the hands and soles of the feet. There are two types of sebaceous gland, those connected to hair follicles, in pilosebaceous (pilo means hair) units, and those that exist independently.
Sebaceous glands are found in hair-covered areas, where they are connected to hair follicles. One or more glands may surround each hair follicle, and the glands themselves are surrounded by arrector pili muscles. The glands have an acinar structure (like a many-lobed berry), in which multiple glands branch off a central duct. The gland forms sebum which flows to the skin surface along the hair shaft via the hair follicle. The structure consisting of hair, hair follicle, arrector pili muscles (“Goosebumps” forms as these tiny muscles pull the hair follicle), and sebaceous gland is known as a pilosebaceous unit.

Factors responsible for initiation and maturation of acne are:

1. Abnormal follicular keratinization
2. Excess sebum production
3. Bacteria known as Propionibacterium acnes
4. Inflammation

Abnormal follicular keratinization

Of note is the fact that keratinization also occurs at the opening of hair follicle, so the process of continuous shedding of keratinocyte is present there as well. In acne, instead of flaking off with the sebum, these keratinocytes clump together along with the sebum to clog opening of pilosebaceous unit.
The trapped sebum, cells, and keratin form a very sticky mixture which plugs the opening just like a cork in a bottle, so the contents of sebum can’t exit onto the surface of the skin The plug is called a microcomedo. The microcomedo is too small to be seen by naked eye. Over time, the increasing amount of trapped sebum builds up a lot of pressure and the hair follicle blows up like a balloon and becomes a visible comedo.

Excess sebum production

Hormones are the body’s chemical messengers used to regulate many body functions. In both males and females, a particular group of hormones, called androgens, are primarily associated with the formation of acne. The term androgen is a general term for hormones that imparts masculine character, quality, or appearance.
The androgenic hormones help us regulate how much sebum our sebaceous glands produce. People who get acne aren’t producing any more of these androgens than anyone else; it’s just that their sebaceous glands are very sensitive to the hormone’s message. The glands respond by pumping out excessive amounts of sebum. As face, chest, and back contain the highest concentrations of sebaceous glands; that’s why these are the most affected sites.
Adolescence is the usual time for acne because androgens are increasing steadily during the teen years, and they make sebaceous glands larger and more active. As adolescence ends, the amount of androgen secretion diminishes and acne tends to disappear for most of the affected people by 25 years of age. But for various reasons, some women (and much less commonly, men) retain a increased sensitivity to their androgens and continue to have acne beyond adolescence. Some women even get acne for the first time as adults (Post-adolescent acne).

Propionibacterium acnes

They are harmless bacteria present on everybody’s skin, residing in sebaceous glands. Human sebum happens to be their diet and while they eat it, the convert the sebum in to fatty acids. Inside a blocked sebaceous gland (comedo) the count of Propionibacterium acnes increases then normal range, so is the amount of fatty acids. The bacteria combined with the force of the trapped sebum, can cause ruptures or leaks in the wall of the comedo, allowing the free fatty acids into the surrounding skin.


Inflammation is a reaction of the skin to disease or injury; in the case of acne, the inflammation is a reaction to the Propionibacterium acnes and to the mixture leaking out of ruptured comedo. Signs of an inflammation include swelling, redness, warmth, and sometimes pain.
However, weather the processes addressed above will lead to the development of acne in an individual fundamentally depends on hormones and heredity.


Interested in knowing more about types of acne, click here.