Pheromones are substances that are released by one animal into the environment that other animals take in through the nose or mouth that "communicate" by changing the physiological state of the second animal (bugs, etc).

Animals have something called the vomero nasal organ that is a primary receptor for pheromones. Humans have this organ, but most scientists think it's vestigial. There is evidence that it is not. For example, women living together in dorms tend to have their periods synchronize. This could be due to keeping similar schedules or living in the same environment. But it could be due to them inhaling molecules of each others' hormones.

Oxytocin is both a brain chemical and a hormone. So it is possible that molecules produced in our bodies could be exhaled and then inhaled by other people.

Whether or not this is true, most things that trigger the oxytocin response (a positive social response to another person) probably come via facial expression, body language and tone of voice.

Here's a scientific paper (pretty readable) that examines the evidence that the human vomeronasal organ may be an organ of human communication.

http://chemse.oxfordjournals.org/content/26/4/433.full.pdf+html

The author, Michael Meredith of Florida State University, comes down on the side of no. But we continually find out more about the human body and what makes us tick. Scientists have discovered, for example, that what they used to call "junk DNA" -- because they didn't know what it did -- turns out to influence gene expression.

I think a lot of people, including scientists, get squeamish about the idea of humans sniffing each other like, well, animals. To me, the jury is still out.

PHOTO: Mark Watson