If humans were like rodents and insects, they’d sniff out body odor from mates with Goldilocks-like immune genes—not too similar, not too different. In a 2002 study published in , researchers focused on the Hutterites, an isolated American religious community descended from a relatively small number of ancestors. But studies of Hutterite spouses showed that partners didn’t tend to have very similar HLA genes.

The researchers wanted to find out if women were sniffing out men with just-right HLA profiles.

A small but growing trend in social media is to go nose first when it comes to romance: whether by throwing get-togethers that hook people up based on the smell of their T-shirt, like Pheromone Parties, or by matching people based on how similarly they smell the world, like the Israeli social network Smell Space.

As a result, smell can trigger thoughts and behaviors very quickly.Researchers agree that our sense of smell is important to human relationships, and that we are hard-wired to be drawn to people whose scent we like—be it from a bottle or their armpits.But the idea that humans emit invisible chemicals that could drive us to a partner is hardly the consensus today. My first boyfriend had a smell I haven’t been able to shake years later, like dirt and earth and just-wet soil.“Isolating the odor part to it has been very, very difficult.” Animal studies are able to control for the diet, genes, upbringing and diseases that alter body odor, but that’s impossible to do in humans.Scientists can also expose lab animals to bodily secretions that would be far too unseemly to use in human studies.