Men who were born without a sense of smell report having far fewer sexual partners than other men do, and women with the same disorder report being more insecure in their partnerships, according to new research. The researchers don't know why romantic difficulties could be tied to smell, but they say one possibility is that people with anosmia, or no sense of smell, are insecure, having missed many emotional signals all their life. "A lot of social signals are transported through the olfactory channel, and they are probably missing them," said lead author Ilona Croy, a psychologist at the University of Gothenburg in Sweden. The findings were published Nov. 22 in the journal Biological Psychology. Social smelling Though no official census of anosmiacs exists, the Anosmia Foundation estimates 2 million to 5 million American adults have taste and smell disorders. Some people are born lacking a sense of smell, while others lose it due to head trauma, nasal growths, radiation cancer treatment, or diseases such as Alzheimer's. A growing body of evidence suggests humans subconsciously transmit emotions via smell. One study found that the smell of fear is contagious, and other work has shown that people can differentiate between the odors of nervous sweat and exercise sweat, and can be influenced by odor signals in choosing a mate. Earlier this year, Croy's team published a study in PLoS One that found those born without an olfactory bulb, or the brain region needed for smell, were more socially insecure and likelier to be depressed than those with an intact sense of smell. Soon afterward, the team was bombarded with questions from researchers wondering how the effects varied by gender. Several studies have shown that women perceive smell differently than men do. So the team reanalyzed the findings by gender. While "smelling" men reported on average having nine sexual partners over their lifetime, anosmic men reported having three. For women, there was no difference in the number of lifetime partners, but they reported being more insecure with their partners than other women reported. (In the study, the average age was about 30 for both the 32 people with anosmia and the 36 people with a normal sense of smell.) Life without smell One possible explanation is that social signals are transmitted by the nose, and anosmiacs are missing those cues, making them feel more socially awkward, Croy said. As a result, men may not be confident enough to seek new partners. "The men may have less exploratory behavior; they are not walking around like, 'Hey, I am the man!'" Croy wrote in an email. For women, this social anxiety may translate into insecure relationships. The idea that anosmiacs are missing subtle social cues isn't far-fetched, said Thomas Hummel, a study co-author and researcher at the Smell and Taste Clinic at the University of Dresden in Germany. "It may well be that we are exchanging much more information through body odors than we are aware of," Hummel told LiveScience. "We are governed by our noses in some ways." In general, those with anosmia are more insecure in daily life — they don't know whether they have bad breath, stinky armpits, are drinking rotten milk or living in fishy-smelling apartments. Constantly wondering whether you smell bad makes a person insecure, and that could spill over into the person's love life, Hummel said. "People say they develop certain routines: So it's mandatory to shower twice daily, they clean their teeth three times a day," he said. "They have all these routines just to prevent themselves from becoming a smelly part of society."