We mechanically rub the area behind the ear or the crease of the nose, and the smell that rises evokes a camembert forgotten on the work surface. This is neither a hygiene problem nor a figment of the imagination: sebum, this oily substance continuously secreted by the skin, indeed develops notes reminiscent of aged cheese. The phenomenon affects almost everyone, but its intensity varies depending on the area of the body, age, and care habits.
Squalene and oxidation: the cheese smell starts before the bacteria
We spontaneously associate bad body odors with skin bacteria. This is partly true, but the mechanism starts earlier. Squalene, the main lipid in sebum, undergoes oxidative degradation upon contact with air. This reaction produces squalene monohydroperoxide and several volatile aldehydes that modify the skin’s baseline odor even before microorganisms intervene.
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In practice, one can smell this “cheesy” note on freshly washed skin, especially in areas with high sebum production: nostrils, forehead, scalp, and around the ears. Oxidation accelerates with heat and sun exposure, which explains why the smell is more pronounced in summer or after moderate physical exertion, even without abundant sweating.
To understand in detail why sebum smells like cheese, one must consider this lipid oxidation as the first stage of the rocket: it establishes an olfactory base that bacteria then amplify.
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Skin microbiome and volatile fatty acids: the same molecules as in aged cheese
The skin hosts a dense bacterial ecosystem, and certain strains literally feast on sebum. Among the most active in this area are Staphylococcus hominis, Staphylococcus epidermidis, and several species of Micrococcus. These bacteria break down the triglycerides in sebum into short-chain volatile fatty acids, exactly the same compounds released during the aging of washed-rind cheeses.
The parallel is not a metaphor: the biochemistry is identical. Isovalric and butyric acids, responsible for the characteristic odor of a munster or an époisses, also form on the surface of our skin when the local microbiome is dominated by these strains. The concentration of these bacteria varies by body area and from person to person, which explains the differences in intensity.
The armpits, often cited when discussing body odors, are actually dominated by other bacterial families (notably Corynebacterium) and produce a more sulfurous olfactory profile. The cheese smell is mainly linked to areas rich in sebum, not necessarily to the most humid areas.
Degreasing sebum and hyperseborrhea: when cleaning worsens the smell
A common reflex in response to this odor: increase cleaning, use abrasive scrubs, raise the shower temperature. In practice, this approach often produces the opposite of the desired effect.
Clinical observations in dermatology show that aggressive and repeated degreasing of sebum triggers compensatory hyperseborrhea. The skin, deprived of its lipid film, produces more to protect itself. This surplus of sebum feeds more bacteria, which release more volatile fatty acids. The skin microbiome becomes unbalanced in the process, favoring the most odorous strains.
The most common situations that worsen the problem include:
- Very detergent makeup removers used morning and night, which dissolve the entire lipid film and force the sebaceous glands to overproduce
- Mechanical scrubs more than once a week on the face, which irritate the skin barrier and alter the resident flora
- Prolonged very hot showers, which dilate the pores and accelerate both sebum secretion and squalene oxidation
The strategy that works best on the ground is to clean without degreasing: a gentle cleanser with a pH close to that of the skin, lukewarm water, and let the microbiome regulate itself. Feedback on this point varies according to skin types, but the general trend is clear.
Diet and sebum profile: what ingested fat changes in skin odor
Sebum does not have a fixed composition. Its fatty acid content partly reflects what we eat. Clinical observations suggest that a diet rich in saturated fats and fermented dairy products alters the lipid profile of sebum in a way that is more conducive to the production of malodorous volatile acids.
This is not a unique cause, and reducing dairy products does not eliminate the smell for everyone. However, in patients monitored for bromhidrosis (excessive body odor), a reduction in these intakes has sometimes perceptibly improved skin odor.
Beyond diet, other factors influence the composition of sebum:
- Age, with a peak in sebum production during adolescence (the carboxylic acids secreted in large quantities during this period explain the “goaty” smell often associated with teenagers)
- Chronic stress, which stimulates sebaceous glands via cortisol
- Certain medications, particularly topical corticosteroids applied long-term
Reducing the cheese smell of sebum without disturbing the skin
Rather than trying to eliminate sebum, it is beneficial to limit its oxidation and stabilize the skin microbiome. Applying a light moisturizing treatment after cleansing reduces the signal of overproduction sent to the sebaceous glands. Formulas containing zinc PCA or niacinamide have shown a sebum-regulating effect without harming the resident flora.
For the most affected areas (creases of the nose, behind the ears, scalp), a targeted rinse with lukewarm water during the day is often enough to limit the accumulation of volatile fatty acids without triggering overproduction.
The cheese smell associated with sebum is not a dysfunction: it is the normal result of the lipid and bacterial chemistry of our skin. Fighting it head-on worsens the problem. Mitigating it involves measured actions, respectful cleansing, and sometimes a look at what’s on the plate.