No, really. What would you do? What scents would you miss the most? Freshly laundered sheets? A certain perfume or cologne worn by someone you care about? Mom/dad/Aunt Jane's meatloaf? The roses in your garden? While I might miss my favorite perfume, I'll tell you what I wouldn't miss: subway body odors. But what about if you never had a sense of smell—how would you even know what to miss? And how would your life be different?
The latter questions were the subject of a paper published in the open access journal PLoS One. The ability to smell can undoubtedly be useful. It can warn you of a gas leak or that the milk or meat you're about to consume is bad. It could tell you that the iron is on or that you've stepped in something unpleasant. It entices us to eat—can you resist the savory smells of your favorite meal? Data from the NIH reports that 1%-2% of people in North America have a smell disorder that may range from the reduced ability to detect odors (hyposmia), which can be a temporary result of having a cold, to the inability to detect odors completely (anosmia). (That percentage rises to 15%-20% when global populations are counted.) Isolated congenital anosmia (ICA) occurs when otherwise healthy people are born without a sense of smell. And it's rare: researchers estimate that 1 in 5,000-10,000 are afflicted (globally). But for those few individuals, how are their lives changed? This was the question that Ilona Croy and colleagues set out to answer:
If the sense of smell is important for ingestive behaviour, environmental hazards and social communication, like described above, how are these domains affected in patients with ICA? Do ICA patients have trouble maintaining their weight or do they obtain no joy in eating, for example? Do they accidentally eat spoiled food? Do they also worry about their body odor? And do they feel different in social situations? Or are people without a sense of smell not affected at all by this deficit and is olfaction just overestimated?
It turns out that these individuals don't experience significant differences in quality of life. In fact, they often don't realize that they're missing anything—and that makes sense: how can you know something is missing if you've never had the item to begin with? Often, anosmia is diagnosed when someone close to the person notices a discrepancy in responses to offensive odors, which researchers believe may indicate that smell may not be as crucial to the ways we experience the world.
A survey of individuals with ICA also reveals that there may be other sensitivities to consider (1). For example, individuals with ICA reported a higher incidence of household accidents and a greater degree of social insecurity. The former relates to things like leaving the iron on or drinking spoiled milk. In this case, individuals reported developing coping strategies—"Hey, does this smell okay to you?"—to reduce difficulties. The latter reflects concerns about social relationships. The researchers propose that olfactory cues can provide important—subtle—information about other people that could help guide appropriate social interactions. In the absence of these cues, having ICA may result in hesitation in social settings. However, the authors are careful to note that additional research is needed to confirm both points.
It makes sense to a certain degree: Anything that might impact your ability to function within a social setting might heighten social insecurity, but it might have less to do with olfactory cues from others, and more to do with concerns about self—along the lines of "Does my breath smell?" or "Is my deodorant still working?". Can you actually smell anxiety? I'm not sure, though you might be able to sense it and read it from body language and in other cues. And if you were in a situation where you could smell the fear on someone else, well, my guess is that you'd already know he was frightened. While pheromones may play a role in mate selection and in influencing behavior, their function in human relations remains somewhat mysterious.
One of the findings from the study is that individuals with ICA report being breast fed as often as controls. The reseachers note that this is somewhat surprising given the importance of smell for infants in locating the nipple. I think perhaps this is less surprising than one might suppose: human mothers can presumably guide their infants to the nipple if needed. Croy and colleagues also note that there does not seem to be noticeable effects on eating behaviors, which they find odd given the link between smell and taste. And while a decrease in appetite is often reported in individuals with hyposmia, the lack of a noticeable effect in eating behaviors in individuals with ICA may be the result of being socialized without a sense of smell. If the individuals and those closest to them are unaware of being different initially, then they're likely not being treated differently at meal times—and we can't forget that we just don't know what the relationship between ICA and taste is.
Ultimately, smell may be less important to daily life activities for humans than for other members of the animal kingdom for whom a sense of smell is tied to daily survival—in part because we belong to social systems that can provide support and help us cope in the face of what might otherwise present a challenge. But this doesn't mean smell is a dispensable sense.
(1). The sample for the survey was small (n=32), but given the rarity of anosmia, this may be suitable for preliminary suggestions.
Croy I, Negoias S, Novakova L, Landis BN, & Hummel T (2012). Learning about the Functions of the Olfactory System from People without a Sense of Smell PLoS ONE, 7 (3)