I bet you heard some version of this before. You might even have said it yourself casually: "I can't wear this as it doesn't mesh with my personal chemistry" or "Oh, you're wearing that one? Must be very suitable to your chemistry, then" or even "I absolutely love this perfume because it melds with my personal chemistry". The way "personal chemistry" is brandished about in scent discussion between wearers, sellers, casual encounters and friends, as well as online partners in communication, one would think we all carry a kit with test tubes and smoking, foamy stuff tucked in our clothes! The truth is of course we don't. Or do we, in some more obscure way than the literal thing?
The term "personal chemistry" was coined to suggest that a person's individual smell (something as unique as a fingerprint, based on many biometric indicators such as general health, hormones, diet etc.) would powerfully react with a given fragrance, nuancing the latter into making it something more than merely what hides within the bottle. The term has also been used as a polite way to infer that you would never in a million years wear something someone else suggests or wears as you don't find it attractive for yourself for whatever reason. These niceties of course give rise to much confusion, at least as much as putting down someone's perfume by claiming you're "suffering from allergies" when in fact you are averse to their particular scent of choice. It's more useful in the long run if one is caring but honest, but I digress.
Despite the fact that the plea for personal chemistry can be a wonderful, romantic, even erotic notion, giving every woman the idea that her fragrance of choice is hers alone, because magically the scent is different in accordance with one's skin, this is largely a (potentially dangerous) myth and a marketing technique rolled into one. I'm using both descriptions purposefully, so let me explain.
A question of dubious politics...
In the beginning of the 20th century, right when modern perfumery really took wings on the heel of late 19th century evolutions in organic chemistry (the first synthetics had really gained ground over the much more complex and expensive naturals, turning fragrance into a democratic luxury), the political milieu of segregation based on gender, race and ethnicity was gaining ground as well, culminating in the fascist regimes that swarmed over Europe and into the Nazi atrocities of WWII. The compartmentalization of human characteristics into "types" relying on complexion and hair color were seemingly innocent enough and venerable houses such as Patou and Guerlain readily suggested their best-selling fragrances according to these guidelines. Thus L'Heure Bleue was for blondes while Mitsouko was for brunettes; or think of the original triptych by Jean Patou from 1925: Amour Amour (i.e. love, love) aimed at blondes, Que sais je? (i.e. what do I know?) intended for brunettes, with Adieu Sagesse (i.e. goodbye wisdom) fit for redheads.
The underlying concept ~which surprisingly gets forgotten when discussed today~ was that most women didn't color their hair at the time. Hair coloring was semi-revolutionary, difficult and expensive and Jean Harlow almost lost all her famously platinum-hued hair due to the frequent peroxiding. No, the concept was based on natural hair color signifying a complexion variance; a natural redhead can't but have the milky white complexion we recognize at a hundred paces. A natural brunette can run the gamut of course, but she's not the same as the redhead, and both blondes and brunettes at the geographic perimeter of the big fragrance brands (France, England, the US, Italy, Germany etc) were only as varied. In certain countries the population was so tightly uniform then as to make even such variances insignificant!
But here is where the dangerous part of the equation comes into play. It's a very small leap from hair color and complexion being part of one's "personal chemistry" into ethnicity (which often dictates those parameters) and race! Therefore we have Bloch, an otherwise capable author, dissecting the human odor and concluding that gender, race, ethnicity and complexion all affect the specific odor of humans in an odd treatise that stinks of racism.
A question of social stratification...
We have progressed from the times when George Orwell famously quipped that the social distinction in the West can be summarized in "four frightful words...the lower classes smell" (in The Road to Wigan Pier, 1937, chapter 8). He nuanced it by saying that "here, curiously enough, the Socialist and the sentimental democratic Catholic of the type of Chesterton [ed.note: seeing dirtiness as self-mortification] join hands; both will tell you that dirtiness is healthy and 'natural' and cleanliness is a mere fad or at best a luxury". Of course such social stigmata today in developed countries at least are taken to be the absolute peak of racism and bias towards specific groups and no doubt they are. After all, there is no one more insistent in deodorising the stench of manual labour by using heaps of soap or in bringing their shoes to an impeccable shine than the laborer, eager to shed the "image". The rise of "clean" fragrances (so on trend since the 1990s) could also be interpreted in the social climb-up-the-ladder in the last three decades, at least in affluent parts of the Western world, of people who would otherwise face a life on a rural environment that would involve the smellscapes they are now eschewing in favour of the exhaust, the rained upon concrete and the cubicle farm. The American urban landscape (excluding specific exceptions) in particular is not only more egalitarian, but -perhaps in accordance- more sanitized in what concerns olfactory miasmata as well.
Can "personal chemistry" be the social frontier revisited, this time ever so subtly so as not to offend? "Get off my side you stinky low class" being translated into "your chemistry doesn't suit the Chanels"? It's a thought... It's certainly ironic that Chanel herself had said of society women frequenting her salon "Ah yes, those women dressed in ball gowns, whose photographs we contemplate with a touch of nostalgia, were dirty... They were dirty. Are you surprised? But that's the way it was."
A question of clever marketing...
The marketing angle of "personal chemistry" in regards to perfume on the other hand was specifically conceived for Chanel No.5. To make the iconic Chanel perfume regain a bit of its individual cachet after the mass popularisation of it, following its exhibition in the army shelves market during the early 1950s, some new approach was needed. According to author Tilar Mazzeo, in her book about the venerable classic and its history, the Wertheimer brothers devised this plan to make No.5 not lose its sense of being a precious commodity even though it had become a bit too accessible. (This was a concern after the infamous days of American GIs photographed standing in a long line to claim a bottle of the classic perfume at the Parisian boutique during Nazi-occupied France). Ads from the 1950s featuring Suzy Parker mentioned "Chanel becomes the woman you are", the verb underlined and bearing the full meaning of both its connotations: that is flatters womanhood, but also that it transforms into the specific woman the consumer is.
The plan worked: The marketing line was added even into commercials well into the 1970s and Chanel never became Coty or Dana.
Personal chemistry: in the end, does it exist?
The truth is most contemporary fragrances -excluding all-naturals artisanal perfumes and a few with a particularly high ratio of natural ingredients in them- small exactly the same on the vast majority of skins. Think about it; this is why we're so quick to recognise their trail on a stranger on the street or across the cinema! It would be counterintuitive to market a perfume that no one recognizes so as to get prompted to get it for themselves.
Skin does play a role into how scent "holds", nevertheless, but not how you think it does! In the movie Chéri (based on Colette's novel by the same name) the older courtesan, played by Cathy Bates, says to her -poignantly coming to terms with aging- peer Michelle Pfeiffer (as Lea) "you retain perfume so much better now that the skin isn't as smooth as it used to be". This very characteristic observation of La Belle Epoque is also confirmed by top perfumers working today, who add that the same applies to people with big pores; which -I infer- might explain just why oily skin (which often is more "porous"/bigger-pored by nature) retains scent better and longer. It might also explain why some obese people are considered "smelly" by some in the general population (it's not that they don't wash enough, but sweat might get trapped in skin folds). A certain Ph imbalance might also suggest a different reaction (a too acidic skin might turn sweeter scents less so or turn things acidic), but that's rather rare to generalize.
The fascinating part is it mostly turns out to be a matter of simple physics, rather than of chemistry! But it all might make you pause and think twice before using the term "personal chemistry" in relation to how you perceive a fragrance so casually.