Acne forms when a skin pore becomes clogged. A skin pore is basically a tiny hair follicle. Attached to this pore are skin oil glands called a sebaceous glands. At puberty, these glands start to produce skin oil, called sebum. Sebum is required for the formation of acne, which is why we start seeing acne when puberty starts.
Sebum and Acne Formation
Sebum production is a normal bodily process. Sebaceous glands release sebum into the bottom of the hair follicle. The sebum then slowly moves up the follicle to the skin surface where it acts to moisturize and protect the skin.
Sebaceous glands are found in the largest numbers on the face and upper body—areas of the skin that are highly prone to acne. Scientists agree that high sebum production levels are a key contributor to acne formation.
There are currently two competing theories that explain how acne is formed, and both include sebum as an integral component:
- The first, and more traditional, theory suggests that acne begins when hormones cause the body to overproduce skin cells called keratinocytes.1Keratinocytes produce a sticky substance called keratin, and the overgrowth of keratinocytes and keratin cause the skin pore to clog. Once the pore is clogged, sebum becomes trapped inside the pore. The trapped sebum leads to the growth of the oil-loving P. acnes bacteria. Both the trapped oil and the growing bacteria cause the pore to swell and sometimes burst, producing the visible acne lesion.
A newer theory identifies inflammation as the initial acne trigger. However, in both of these theories, the sebum, which becomes trapped within the clogged skin pore, plays a key role in acne formation.1
Sebum Levels in Acne Patients
The amount of sebum that an individual produces is a primary factor in acne formation. Compared to individuals without acne, acne patients generally have enlarged sebaceous glands. As a result, acne patients generally produce more sebum than individuals without acne.2In fact, one effective yet controversial acne drug, isotretinoin (Accutane®), is known to dramatically and permanently shrink sebaceous glands and reduce the body’s production of sebum. Scientists surmise that the primary reason isotretinoin is effective against acne is that it reduces sebum levels. Whether it is a good idea to permanently reduce the production of sebum remains hotly debated, particularly with people concerned that this may lead to premature aging.
The Role of Male Hormones
What determines the size of sebaceous glands and how much sebum a person produces? Scientists think that the driving force is androgens, which are male hormones that are present in both males and females. Testosterone is an example of an androgen. Generally speaking, the more androgens in the blood stream, the more sebum the body produces.
High levels of sebum production and acne are most common when androgen levels are high. For example, acne is almost never seen during childhood, when androgen levels and sebum production levels are low. At the onset of puberty, androgen levels rise, sebaceous glands enlarge and produce more sebum, and acne forms. As further evidence of the link between androgens and sebum production, castrated men are deficient in androgens, produce less sebum than normal men, and do not develop acne. Castrated men will, however, develop acne if given supplemental testosterone.2,4
The Composition of Sebum and Its Relationship to Acne
Sebum is an oil consisting of several different types of fat molecules. The composition of different fat molecules in sebum is important to acne formation and, in fact, as researchers from a study published in 2014 in the Journal of European Academy of Dermatology and Venereology explain:
“[E]merging data . . . indicate that sebum composition may be more important for the development of acne lesions than the secreted amount.”5
One type of fat molecule found in sebum is called a free fatty acid.6Scientists have found unusually high levels of fatty acids in comedones (clogged pores), suggesting that an increase in the fatty acid content of sebum may play an important role in pore clogging. Specifically, scientists have shown that fatty acids trigger the body’s production of a specific inflammatory substance called Interleukin-1, which is known to trigger acne.5
Other molecules in sebum can also trigger acne. For example, a fat molecule called squalene may cause pore clogging. Squalene triggers inflammation, causing the body to produce a different inflammatory substance called Interleukin-6. Squalene can also lead to an excessive growth of skin cells, and this overgrowth can clog skin pores and lead to acne.5
We have seen that too many free fatty acids and too much squalene may lead to clogged pores, but on the flip side of the coin, when another component of sebum is reduced, we tend to see more acne. That substance is called linoleic acid. Scientists have found that comedones (clogged pores) contain lower than normal concentrations of linoleic acid. Linoleic acid is important for a strong skin barrier. Reduced linoleic acid can weaken the skin and can make the skin pore more susceptible to damage from inflammation.3
Sebum is necessary for acne formation. Increased sebum production, driven by higher than normal androgen levels, increases the formation of acne. When it comes to sebum composition, more free fatty acids and squalene, and less linoleic acid are also thought to potentially initiate acne formation.