Sebum (the oily substance produced by sebaceous glands) doesn’t just increase during acne—it also changes in composition, and those changes can contribute to clogged pores, inflammation, and bacterial overgrowth.
Here’s how sebum evolves during acne development.
1. Normal sebum composition
Healthy human sebum is a mixture of:
- Triglycerides and free fatty acids (~55–60%)
- Wax esters (~25%)
- Squalene (~10–15%)
- Cholesterol and cholesterol esters (~5%)
This mixture:
- Lubricates the skin
- Helps maintain the skin barrier
- Contains antimicrobial lipids
- Reduces water loss
In healthy skin, sebum supports rather than harms the skin.
2. Increased sebum production
One of the earliest changes in acne is increased sebum output, largely driven by androgens (such as testosterone and dihydrotestosterone).
More sebum means:
- Oilier skin
- Greater accumulation inside hair follicles
- More nutrients available for bacteria such as Cutibacterium acnes
However, quantity alone does not explain acne. Many people with oily skin never develop significant acne.
3. Changes in lipid composition
Researchers have found several important compositional changes.
Lower linoleic acid
One of the best-established findings is a reduction in linoleic acid within follicular sebum.
Consequences include:
- Weaker skin barrier
- Increased follicular wall permeability
- Greater irritation
- Abnormal keratinization (skin cells stick together more easily)
This promotes formation of the microcomedone, the earliest acne lesion.
Increased squalene oxidation
Squalene itself is a normal component of sebum.
During acne:
- Reactive oxygen species oxidize squalene.
- Squalene peroxide forms.
Squalene peroxide can:
- Trigger inflammation
- Stimulate excessive keratin production
- Damage follicular cells
- Recruit immune cells
It is considered one of the major biochemical triggers in early acne.
Altered free fatty acids
Sebum triglycerides are broken down by bacterial lipases into free fatty acids.
These fatty acids:
- Irritate the follicle
- Activate inflammatory pathways
- Alter skin pH
- Promote immune activation
Not all fatty acids behave the same way:
- Some are anti-inflammatory.
- Others strongly promote inflammation.
The overall balance shifts toward a more inflammatory environment.
4. Changes in wax esters
Wax esters may become altered in chain length and saturation.
Possible consequences include:
- Increased viscosity of sebum
- Reduced flow out of follicles
- Greater likelihood of pore blockage
This makes comedone formation more likely.
5. Changes in cholesterol metabolism
Studies suggest abnormalities in cholesterol synthesis and esterification within sebaceous glands.
Potential effects:
- Altered sebocyte maturation
- Abnormal skin-cell shedding
- Increased follicular plugging
Research in this area is still developing.
6. Oxidative stress increases
Acne-associated sebum contains more oxidized lipids.
Examples include:
- Oxidized squalene
- Oxidized fatty acids
- Lipid peroxides
These oxidized lipids:
- Activate inflammatory signaling pathways
- Increase production of cytokines such as IL-1
- Promote recruitment of neutrophils
- Worsen redness and swelling
7. Interaction with Cutibacterium acnes
Sebum changes alter the follicular environment.
C. acnes:
- Uses triglycerides as an energy source.
- Produces lipases that generate more free fatty acids.
- Forms biofilms in some follicles.
- Activates innate immune receptors.
Importantly, acne is not simply an infection. C. acnes is a normal member of the skin microbiome, but shifts in sebum composition and the immune response can allow certain strains to contribute to inflammation.
8. Progression through acne stages
The changes can be viewed as a sequence:
| Stage | Sebum change | Result |
|---|---|---|
| Increased androgen stimulation | More sebum production | Oily skin |
| Reduced linoleic acid | Barrier dysfunction | Follicular plugging |
| Increased viscosity | Poor sebum flow | Microcomedone formation |
| Squalene oxidation | Oxidative stress | Early inflammation |
| Bacterial lipase activity | More free fatty acids | Increased inflammation |
| Immune activation | Cytokine release | Papules and pustules |
| Severe inflammation | Tissue damage | Nodules and possible scarring |
Key takeaway
Acne is associated with both more sebum and different sebum. Compared with healthy skin, acne-prone sebum tends to have:
- Increased overall production
- Lower linoleic acid content
- More oxidized squalene
- Higher levels of pro-inflammatory free fatty acids
- Greater lipid oxidation
- Altered wax ester and cholesterol composition
These biochemical changes make the follicle more prone to clogging, create an environment that favors inflammatory responses to C. acnes, and drive the progression from a microscopic clogged pore to visible inflammatory acne lesions.
