The Relationship Between Acne and the Pilosebaceous Unit

A disorder of this unit causes acne

Teenage boy cleaning his acne. Credit: BSIP/UIG / Getty Images

The average person is familiar with acne but mention the pilosebaceous unit, and you're likely to get blank stares. Learn what the pilosebaceous unit is and its connection to acne with this review. 

Why Disorders of the Pilosebaceous Unit Cause Breakouts

The pilosebaceous unit consists of the hair shaft, the hair follicle, the sebaceous gland, which makes sebum, and the erector pili muscle, which causes the hair to stand up when it contracts.

All acne is a disorder of the pilosebaceous unit. These units are found everywhere on the body except on the palms, soles, top of the feet and the lower lip. The number of pilosebaceous units is greatest on the face, upper neck and chest, all common places for acne breakouts. 

Sebaceous glands produce a substance called sebum, which is responsible for keeping the skin and hair moisturized. During adolescence sebaceous glands enlarge and produce more sebum under the influence of hormones, also called androgens. After about age 20, sebum production begins to decrease. This is why acne is commonly thought of as a skin disorder of the teens, but acne can last well into adulthood as well or be triggered by conditions, such as pregnancy, that affect the hormones.

Acne & Bacteria

A bacteria known as Propionibacterium acnes is a normal inhabitant of the skin. It uses sebum as a nutrient for growth and increases in follicles during puberty.

People with acne have more Propionibacterium acnes in their follicles than people without acne.

The presence of bacteria attracts white blood cells to the follicle. These white blood cells produce an enzyme that damages the wall of the follicle, allowing the contents of the follicle to enter the dermis.

This process causes an inflammatory response seen as papules (red bumps), pustules, and nodules. The bacteria also cause the formation of free fatty acids, which are irritants, increasing the inflammatory process in the follicle.

Normal Follicles

Sebum produced by the sebaceous gland combines with cells being sloughed off within the hair follicle and "fills up" the hair follicle. When the follicle is "full," the sebum spreads over the skin surface giving the skin an oily appearance. When this process works correctly, the skin is moisturized and remains healthy.

Obstructed Follicles

Problems arise when the sebum is trapped in the hair follicle. For reasons that are still unclear, some hair follicles become obstructed. The sebum is produced but gets trapped on the way out, and the cells that are normally sloughed off become "sticky," plugging up the follicle.

The process of obstructing follicles is called comedogenesis. It causes some follicles to form a type of acne called comedones, also known as blackheads and whiteheads.

Wrapping Up

If you have moderate or severe acne, you'll likely need to see a dermatologist to get the skin condition under control. While over-the-counter products with ingredients such as salicylic acid and benzoyl peroxide may help treat mild acne, you'll need stronger treatments, including antibiotics, prescription-strength creams or oral contraceptives, to tackle moderate and severe forms of the disorder.


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