The first molecule to challenge the notion that women smell more efficiently than men is revealed, having the dubious ~but fascinating too~ privilige of being the one which also activates OR1D2; that's the human olfactory receptor which, besides being found in the human nose, is also expressed in human sperm cells! Yes, sperm cells actually "smell" all right! The molecule is the aldehyde Bourgeonal and it smells of lily of the valley, also known and referenced as muguet. (Makes you rethink that green Ajax Fête des fleurs you've been using to mop your floor, doesn't it?)
So, do the little swimmers go straight for the dip into your lily of the valley lathered and scented, ahem, private parts? (Lily of the valley substitutes have been for long used in soap making). But before you go out of your way to also clear the shelves of your closest perfumery hall off their stock of Diorissimo and Envy, take a moment to think and appreciate the facts:
It's Bourgeonal alone which activates testicular odor receptors [Science, 2003] and not another lily of the valley aromachemical and it was one among 100 ingredients screened for receptor activation abilities. Bourgeonal just happened to be one of them, which doesn't exclude that there may be others, even more capable of the job. German scientist Hanns Hatt is nevertheless so convinced that he wrote a book (in German) touching upon it with the title: "The lily of the valley phenomenon: All about smell and how it affects our lives". (There could be hundreds of applications in either fertility or contraception products in the future, I guess, not to mention a distinct stirring of the market off the pheromones and into muguet territory! Think about that for a moment...).
The beginning of the research on sperm odour receptors predates this: "Dr. Parmentier, working with researchers in Holland and France, accidentally discovered the sperm receptors while looking for genes that help control thyroid hormones. Using a technique called polymerase chain reaction to scare out even shadows of gene activity from tissue samples, they stumbled on a family of receptor genes active in male germ cells, the precursor tissue that matures into sperm". [source]
To revert to bourgeonal, according to the snippet which I found at First Nerve, where the news was posted, "Peter Olsson and Matthias Laska at Linkőping University in Sweden have finally found a molecule that men detect at reliably lower concentrations than women. It’s an aromatic aldehyde called bourgeonal and as we shall see it’s an interesting molecule for other reasons. [...] Bourgeonal is a potent molecular signal that is critical to sperm chemotaxis, In other words, it’s what sperm use to find their way to the egg. So it makes more than a little evolutionary sense that bourgeonal detection is ramped up in men and their gametic representatives". Of course, Dr.Avery Gilbert has the right humorous tone of telling the facts, so go over and take a read.
But where does the attracting ingredient come from, biologically speaking? "Is it the egg itself, or some other part of the female reproductive tract? 'It could be that the egg is releasing an attractant that helps guide the sperm to the egg, but the problem is that we don't yet know whether, in fact, the egg is the source of that attractant,' Donner Babcock says". [source]
Searching around the Internez I found a post from Jenny van Veenen in Perfume Making back from August 2007, in which she tackles exactly bourgeonal for it sperm kinetics capabilities. The VERY interesting fact and with an especially related connection to perfumes is that "the aroma chemical 'Undecanal' (Aldehyde C-11 undecylenic, waxy/fatty/rose/citrus odor) appears to block the effect of Bourgeonal and inhibits the chemo sensory response in sperm cells. " So watch out those aldehydes if you're trying to get pregnant, you might check out the products you use or if you're trying to avoid getting pregnant you might embrace undecanal etc. A brave new world indeed.
More reading: NY Times , Health 24 and 3Sat (in German)
pic from Perfume Making