Investigating the love lives of the men and women who have no sense of smell

Around 1 in 7,500 otherwise healthy people are born with no sense of smell, a condition known as isolated congenital anosmia (ICA). So dominant are sight and hearing to our lives, you might think this lack of smell would be fairly inconsequential. In fact, a study of individuals with ICA published last year showed just how important smell is to humans. Compared with controls, the people with ICA were more insecure in their relationships, more prone to depression and to household accidents.

Now, in a follow-up paper involving the same 32 patients with ICA, Ilona Croy and her colleagues have looked at how this lack of a sense of smell affects their sexual relationships. The researchers' analysis uncovered an intriguing sex difference. Compared with 15 age-matched controls, the 10 men with no sense of smell reported having substantially fewer sexual partners in their lifetime (male controls averaged five times the number of partners). In contrast, women with no sense of smell averaged just as many sexual partners as women with smell.

On the other hand, the 22 women (but not the men) without a sense of smell tended to report feeling more insecure in their relationship with their current partner, than did the healthy controls. This insecurity was specific to their sexual partner and wasn't found in relation to friendships or maternal attachment.

Across both sexes, the impact of a loss of smell makes sense given the mounting evidence for the social importance of smell, for example we can use smell to detect other people's anxiety; people with more empathy are more likely to remember your smell; and smells convey at least some personality traits. Also, common sense suggests people without a sense of smell might worry about any odours they could be exuding without their knowledge. But the question still remains – why should not having a sense of smell affect men and women differently?

The researchers surmised that not having smell reduces men's "exploratory sexual behaviour", perhaps due to their lack of social confidence. Consistent with this interpretation, there was a negative correlation between the male (but not female) patients' levels of social insecurity and their number of sexual partners.

On the other hand, the researchers think the effect of a lack of smell on women makes sense in light of past research suggesting that smell is more important for their relationship security, than it is for men. For instance, a study published in 2008 found that a half of the women surveyed had worn someone else's clothes (usually a partner's) because of its smell, compared with just 13 per cent of men. Also relevant – the female patients' had lower social confidence than the female controls, and this correlated with their lack of relationship security.

Other research has shown that odour is more important to women than it is to men in choosing a partner: women supposedly prioritise good odour over good looks, men the opposite, although it's not clear how this fits with the current findings. Women also seem to have a superior sense of smell, on average, compared with men, and value the sense more highly.

Croy and her colleagues acknowledged the need for caution given their small sample size, but they said their results emphasise "the importance of the sense of smell for intimate relationships."

Further reading

Croy, I., Bojanowski, V., and Hummel, T. (2013). Men without a sense of smell exhibit a strongly reduced number of sexual relationships, women exhibit reduced partnership security – A reanalysis of previously published data. Biological Psychology, 92 (2), 292-294 DOI: 10.1016/j.biopsycho.2012.11.008