Human skin, all over the body but particularly on the face, is covered by an oil called sebum. Sebum is produced by glands attached to each skin pore. After the glands produce sebum, it slowly makes its way up the pore and is released onto the surface of the skin.1
Humans produce different amounts of sebum and thus have skin types, ranging from dry to oily. Conventional wisdom suggests that oily skin is the skin type most prone to acne, and there is ample scientific evidence to back up this assumption. However, the likelihood of developing acne depends on more than just the amount of skin oil present.
The Function of Sebum
Sebum is not necessarily a bad thing. It helps prevent water loss from the skin, defends the skin from microorganisms, and can aid in preventing some types of skin inflammation.
However, too much sebum can lead to more acne, especially if the sebum has a skewed composition which causes it to irritate the pore. Exactly how the composition of sebum contributes to acne is unknown, but as we’ll see, we do know that the more total sebum someone has, the more that person is usually susceptible to acne.
There are four major skin types:
Dry, normal, and oily skin are all pretty straightforward. They are what they are. However, people with combination skin have dry, normal, and/or oily skin in various areas on their face. The most frequent case with a combination skin type is that a person will have oily skin on their forehead, nose, and chin (called the T-zone) but have normal or dry skin on their cheeks.2
Skin Oil Measurement
How do you know what type of skin you have? Individual skin type is usually measured simply by subjective personal assessment. This means that a person decides on their own whether their skin looks and feels oily, dry, normal, or a combination of these types. This is not an accurate method, though. Opinions of skin oiliness may differ from person to person, and objective methods of assessment are needed for scientific research. As one prolific acne researcher stated, “…an individual’s feelings on the topic of facial sebum secretion are too subjective, and signiﬁcant discrepancies exist between such subjective descriptions of facial skin type and objective measurements. Thus, facial skin type determinations should be performed using objective measuring devices and guidelines for skin typing.”2
Fortunately, there is an objective, scientific method of measuring skin oil amount. This is done with a device called a Sebumeter. This helps determine exact skin oiliness levels and is critical for scientific studies on skin oiliness. However, very few people ever have the opportunity to get a Sebumeter reading, so in the real world, determining your skin type really does come down to subjectivity.
The way a Sebumeter works is relatively straightforward. First, a translucent strip is pressed against the patient’s skin for 30 seconds. This strip will absorb sebum and become transparent. The more sebum the strip absorbs, the more transparent it becomes. The Sebumeter then measures the transparency level of the strip and translates this amount of transparency into something called the casual sebum level (CSL). The CSL is measured in micrograms per square centimeter (µg/cm2) and is used to define specific areas of the skin as dry, normal, or oily. The CSL ranges for each of these skin types in different facial areas are defined in the table below.2 If readings come back different on different areas on the face, that means someone has combination skin.
What Is the Evidence That Oily Skin Is More Prone to Acne than Normal Skin?
A number of studies performed have strongly supported the connection between increased skin oil production and acne development. However, the exact way in which sebum production causes acne is still unknown.
A study published back in 1983 in the Journal of the American Academy of Dermatology compared 12 participants with mild-to-moderate acne to another 12 other participants without acne. Both sets of 12 patients included people with similar ages and genders. The researchers determine the sebum excretion rate, which is the measurement of the amount of skin oil production, in each participant. As the researchers expected, they found that all the subjects with acne had a higher sebum secretion rate than the subjects without acne. In fact, there was a very strong correlation between acne incidence and high sebum excretion rate. This suggests that oily skin is more prone to acne than normal skin.
Furthermore, this study also found a link between acne severity and sebum secretion rate. Subjects with moderate acne had twice the sebum secretion rate of subjects with only mild acne.4
South Korean studies: A series of studies on the relationship between skin oiliness and acne have been published by South Korean researchers in recent years. In the first study, published in the British Journal of Dermatology in 2005, researchers determined the casual sebum level (CSL) of 46 female patients with acne and 46 female patients without acne by using a Sebumeter, as well as the skin type of all these patients. The CSL numbers were considerably higher in patients with acne than in the control group with no acne. This finding strengthened the case for oilier skin being more prone to acne.5
The second South Korean study was published in 2006 in Archives of Dermatological Research and was led by the same researcher as the study above. This study compared 23 females and 13 males with acne to a group of 23 females and 13 males without acne. The CSLs were determined on five regions of the face for each of these patients: the left cheek, right cheek, chin, nose tip, and forehead. Every area of the face had slightly higher CSL numbers in the patients with acne versus the patients without acne, with the exception of the nose tip. The nose tips had much higher CSL numbers in the acne patients when compared to the acne-free patients.6Once again, these findings suggested that people with acne tend to have oilier skin than people without acne.
The same lead researcher also published more findings in 2013 in the Journal of the European Academy of Dermatology and Venereology from a study with a much larger sample size. This study examined the cases of 278 male and 636 female acne patients from 2004 to 2009. For each patient, the CSL values of their cheeks and their T-zone (the forehead, nose, and chin) were determined. The number of comedones (whiteheads and blackheads), inflammatory lesions, and total number of acne lesions, which was comedones plus inflammatory lesions, on each patient’s face was also counted. Just like in the previous studies, the researchers found a correlation between higher CSL values and the amount of acne. Specifically, higher CSL numbers, or more oiliness, were consistent with more inflammatory lesions. This held true for every area of the face—the cheeks, T-zone, and the entire face. Since this 2013 study utilized a larger sample size, these findings were considered more reliable than the previous studies above. The researchers concluded that the greater amount of skin oil a person has, the more likely they are to develop acne.7
Increased Sebum Production Is Not the Only Factor That Contributes to Acne
Every study above found that increased skin oil production is associated with acne. However, inflammation, bacterial colonization on the skin, and increased skin cell growth also contribute to acne development.8
All of these other circumstances, including sebum production, can influence each other. For example, increased sebum production can stimulate the growth of acne bacteria, and acne bacteria can help to trigger inflammation.
The exact sequence of these events is still unknown, and we do not yet understand the exact way in which each of these factors influences acne development. But one thing research agrees on is that oilier skin is more prone to acne.