The cells in the human body that keep out foreign invaders apparently influence a person's odor. And now synthetic chemicals that mimic this scent could one day be added to perfumes to lure potential mates, a new study suggests.
The study, published today (Jan. 22) in the journal Proceedings of the Royal Society B, found that women preferred wearing perfumes with an odorless substance that mimics unique immune system chemicals secreted through the skin.
Some people's immune systems can be incompatible with each other— either leading to offspring with a poor defense against invaders or a tendency to attack the body's own cells. So, if added to perfumes, the synthetic chemicals could one day broadcast people's immune signature to lure the most evolutionarily compatible mates. [10 Odd Facts About the Female Body]
The findings suggest that body odor does carry clues to the type of immune system someone has, said Cristina Davis, a University of California, Davis researcher who studies body odor and its relation to immune status, but was not involved in the study. In addition, the study suggests that "the sense of smell might affect behaviors, and one of those behaviors might be mate selection."
Ancient selection tool
Vertebrates from stickleback fish to humans have highly unique proteins on their cells that help these cells recognize foreign invaders such as bacteria or viruses. And across species, these immune fingerprints called major histocompatibility complexes (MHCs) seem to play a role in mate choice, said study author Manfred Milinski, an evolutionary biologist at the Max Planck Institute for Evolutionary Biology in Germany.
For instance, research has found women prefer sweaty T-shirts from men who have MHCs that are not too similar to or not too different from their own. And past work showed that people's MHC genes guide perfume preference.
That led Milinski and his colleagues to wonder why humans slather on perfume — and why perfumes have remarkably consistent ingredients across cultures.
"Perfumes have been used in all populations around the world since we have written history," Milinski told LiveScience.
Secret to perfumes?
One possibility for the popularity of perfume was that classic perfume chemicals mimicked immune chemicals.
To find out, the team created synthetic versions of portions of the MHC molecules.
Then they had a group of 22 women apply four different versions of a perfume under their arms over two different nights. The consciously detectable smell was identical, but one contained an MHC-like molecule similar to those produced by their own immune system, while the other armpit had a foreign MHC mimic.
Women who didn't have colds and didn't smoke consistently preferred to wear the mixtures that "smelled" like their own immune system, suggesting that they were subconsciously broadcasting that trait.
"This tells you it is not your free will to decide what kind of perfume you like on yourself, it's dictated by your MHC genes," Milinski said.
The findings could be used to create synthetic perfume chemicals that could broadcast a person's immune signature as a lure for potential mates.
These synthetic molecules could then replace chemicals such as amber, which is produced from the indigestible remains of whale meals, or musk, which comes from deer gland secretions, Milinski said. Those ingredients are increasingly being outlawed in Europe because of allergic reactions, he said.