Definition
Skin chemistry is the set of factors specific to each person that change how a perfume renders: skin pH, amount of sebum, hydration, body temperature, and, more indirectly, diet. These variables act on how fast molecules evaporate and on the balance between notes, so the same juice does not exhale exactly the same accord on two different skins. The pH of the skin surface, called the hydrolipidic film or acid mantle, averages around 4.5 to 5.5, a slightly acidic medium.
Skin chemistry is neither a myth nor a universal explanation. It is a set of real physico-chemical mechanisms, but whose effect stays moderate next to the variability of olfactory perception itself.
Detail and Context of Use
Skin pH influences the rate of hydrolysis, that is, the cleavage of certain chemical bonds by water. On more acidic skin, citrus top notes rich in volatile esters open more sharply but burn through their fuel sooner; on less acidic skin, the same opening is quieter and sometimes a little more tenacious. Fragrance formulas, for their part, are generally compounded near neutral pH, so meeting the acid mantle shifts the balance slightly.
Sebum plays the most tangible role in longevity. The skin's oils bind to the odorous molecules and release them slowly: oily skin holds a perfume better and longer, while dry skin, poor in lipids, lets it evaporate faster. This is the practical reason for advising a moisturizer or a neutral balm before perfume on dry skin.
The Factors That Shape the Rendering
Five individual factors recur in the literature. None acts alone; they combine on each skin.
| Factor | Effect on rendering | Direction of the effect |
|---|---|---|
| Skin pH (about 4.5 to 5.5) | Hydrolysis rate, top-to-base balance | More acidic skin: sharper, more fleeting opening |
| Sebum | Fixing of the odorous molecules | Oily skin: better longevity and projection |
| Hydration | Lipid support to grip the perfume | Hydrated skin: extended longevity |
| Body heat | Volatility, sillage diffusion | Warm skin: stronger but shorter diffusion |
| Diet | Indirect modulation of body odor | Real but diffuse and poorly quantified effect |
Skin temperature also explains why the same perfume seems more expansive in summer or after exertion: heat speeds evaporation, at the cost of shortened longevity.
The Osmetheca View
Skin chemistry is real, but it is overinvoked. It is conveniently blamed for every difference in perception, when a large share of those differences comes from two phenomena that have nothing to do with the skin. The first is olfactory habituation: wearing a perfume long enough, you stop smelling it on yourself, not because your skin "ate" it, but because your nose has grown used to it. The second is selective anosmia: some people cannot detect a given molecule, musks in particular, and will call a perfume "weak" when it projects perfectly well to everyone else.
Crediting skin chemistry with what stems from habituation or partial olfactory blindness leads to false conclusions, such as believing a perfume "does not last on me" when it lasts perfectly well for those nearby. The sound method is to cross-check: ask a third party, test on a blotter as much as on skin, and distrust the reflex that makes the skin the cause of everything.
See Also
Sources
- Société Française des Parfumeurs, parfumeurs.fr, notions of longevity and skin support.
- Ellena, J.-C. Perfume: The Alchemy of Scent. Arcade Publishing, 2011 (evaporation and rendering on skin).
- Now Smell This, pieces on olfactory habituation and selective anosmia.
- Dermato-cosmetic literature on the acid mantle (average skin pH 4.5 to 5.5).