Study Finds 30% Difference in People’s Scent Receptors

I’ve been talking about this for years on my blog based on my experiences with testers during the process of creating scents, and the studies keep coming in to support what we perfumistas have suspected for ages: our different sets of scent receptors in our noses make us smell scents differently. A study by Monell Chemical Senses Centre in Philadelphia (published in the Nature Neuroscience Journal) found that 30% of scent receptors can vary from one person to the next. That’s a surprisingly big difference.

We tend to be quick to say that a scent doesn’t smell good on our skin when we dislike something and don’t want to hurt the feelings of fans of the scent, but it can be both our skin and our noses that are different. Sometimes you can put the same scent on two different people and the same nose will smell it differently on those people. But if many different people smell the same scent on a paper strip, taking skin out of the equation, they will experience it differently. Their receptors will pick up different aroma molecules in the scent to different degrees, changing the scent experience.

This is partly why it is impossible to create a universal scent that everyone loves and why we need options to choose from (though maybe not as many options as the crazy explosion of new scent offerings in recent years!). It’s also why you’ll see different people online describe the same scent so differently, and why it’s important to try samples for yourself rather than going by what others say. And of course, personal preferences based on experiences and upbringing are added on top of genetic scent receptor differences, which further complicates the scent experience.

If you are interested in this topic, the article at the link is worth a quick read. You can find other posts on my blog on this topic by clicking on the tag “genetics” below this post.

More Discussion About Individual Scent Perception

I’ve been talking about the topic of scent perception for several years on this blog, and here’s another interesting, though limited, study showing that we each smell things a little differently. Thanks to Robin at Now Smell This for the link.

This investigation found that almost everyone was anosmic to some ingredient in the study, and those anosmias of course influence the way people smell fragrance blends that include the ingredients they can’t smell. The author said she discovered that she can’t smell galaxolide, which is a common musk (it’s a polycyclic musk very common in laundry products but on the decline in fine fragrance now that we are moving to biodegradable macrocyclic musks instead). I’ve found people are commonly anosmic to things besides musks, like ISO E super, ambroxan, other synthetic ambers, and salicylates. They are less commonly anosmic to naturals since traditional botanical natural extracts are composed of many chemicals, but they can be anosmic to natural isolates that are a single chemical. Sometimes people can also be nearly anosmic to more complex naturals like ambrette seed, being only able to smell them a little bit.

Once again this poll found everyone liked the scent of vanilla; we’ve seen that in previous studies. The author also found that Asians rated the scent of rose higher than other ethnic groups did, and that’s interesting to me because Velvet Rose is very popular with my customers in Japan. I’ve wondered if Velvet Rose received some word of mouth recommendation in that market circle or if there is a cultural preference for rose soliflores too — I’d love to know if rose scents are popular in Japan.

The author also mentions the way people describe scents using different terminology, but you have to be careful there because often people really do smell the same thing but just describe it differently. People who don’t study perfume or scent don’t have the vocabulary that we perfume lovers take for granted, so terms like “green” to describe a smell can seem foreign to them at first, and terms like “aldehydic” won’t be used at all by someone not familiar with fragrance. She mentions isoeugenol, which is an aroma chemical that smells like clove and is used in carnation accords as well as many other types of scents. People can smell isoeugenol and describe it as floral or spicy since it may remind them of clove or of carnation/dianthus flowers. Isoeugenyl acetate is more floral (to my nose anyway), and is gentler.

I have found it interesting to watch these studies continue to trickle in over the years, given that this variation in scent perception is an issue that perfumers have long grappled with. It’s good to see smell research continue; I hope we’ll come to understand how we smell as we research it more.

Here are some of the other posts I’ve made on this topic:
More On The Sense of Smell
Every Human May Have A Unique Nose
Possible Reasons For Why We Differ In Our Perception Of Scents
Our Own Scent Truth

More on the sense of smell

Now Smell This linked to an interesting article today on Yahoo News titled Super Sense of Smell Not Innate (by Marlowe Hood on Wed March 9). The article discusses how perfumers gain much of their ability to detect and identify scents through years of training and experience rather than being born with these skills. It also mentions the ongoing theme we’ve discussed here before concerning the differences in the way people experience the same scents (for example this post and this post and this post).

An excerpt from the Yahoo News article:

“Patrick MacLeod, former head of the Laboratory for Sensorial Neurobiology, near Versailles, says that olfactory thresholds vary dramatically.

“No two people will ever smell the same thing in the same way,” he noted. “When we perceive an odour the exact nature of the sensation that is produced depends as much on the observer as the object.”

In experiments, he has shown that a small quantity of a given molecule may be imperceptible for one person and easily detected by another. For a different chemical, it may be the reverse.

These thresholds can easily vary from one person to the next by a factor of a thousand.

Mac Leod also points out that the human genome contains nearly 350 olfactory genes — far more than for vision or hearing — resulting in highly individualised odour detection.”

When I send samples out to testers, I do see these differences in sensitivities to ingredients. I try to distinguish between people’s preferences and the way they smell a scent because both will determine whether a scent works for them, and differences in people’s skin will add yet another variable. Several questions become relevant. Does the tester like the smell of some ingredient like ambroxan or cosmone musk or jasmine sambac, etc? How strongly does the tester smell it, from being very sensitive to being average to being anosmic to it? And how does it do on the tester’s skin? Of course interactions between ingredients affect the outcome too, so I need to think about both the parts and the whole. It’s a fascinating topic to me.

Another tidbit on scent perception differences between people — “Every Human May Have A Unique Nose”

A few weeks ago, Robin on Now Smell This posted a link to a series of videos for a symposium called Headspace that covered topics on “Scent As Design.” I played the videos in the background while I worked on something else, and I found part of one of the four to be interesting enough to go back and watch in more detail. The one that caught my attention was a presentation by Leslie Vosshall about the way people smell the same scent differently. I’ve talked about this phenomenon on the blog a number of times, so it was interesting to see that some researchers are currently looking into it. For those who are curious, the link is symposium part 3, and this topic starts at about the 25 minute mark.

Researchers at Rockefeller University studied how people perceived different odors and took blood samples from the subjects to study their DNA. The researchers found that each person had a different set of odor receptors that were functional and nonfunctional, and those differences seemed to make people perceive the odors differently. The title for that slide during the lecture was “Every Human May Have A Unique Nose.” The topic came up again at the 1 hour and 4 minute mark when they compared having nonfunctional odor receptors to being color blind but with much more subtle results since there are so many more odor receptors than color receptors, which means that losing a few makes less impact on your life for smells than for colors.

Leslie Vosshall also mentioned that they found a core set of odor receptors that almost everyone had, and vanilla was one of those with only 5 percent having nonfunctional vanilla reception. That does not surprise me since I’ve yet to find someone anosmic to vanilla, while I’ve found people anosmic to many other things. As a perfumer this makes me feel it is “safer” to use vanilla as a sweetener than to use musk, and I’m more aware of this issue now than I was several years ago. It may also help explain why vanillic bases are so popular — not only are they long-lasting, but they are also more likely to be smelled by nearly everyone.

Our own scent truth

I’ve found it very interesting to see the variation in how people perceive a scent, and part of the reason for the variation seems to be that for any given note or ingredient people have different sensitivities and tolerances to it. What is often called “skin chemistry” also plays a role, but even if you eliminate skin differences by having people smell scent strips, they will still describe a scent differently, and the differences go beyond semantics. I see a sort of a bell curve effect, where the majority of people experience the basic aspects of a scent in the same way but differ in the details, while a few people at the outside edges of the curve experience the scent completely differently, maybe because they are anosmic to some major components and/or extra sensitive to others.

For example, most people who sniff Rose Musc smell both the rose and musk components, plus labdanum and ambergris. Some smell more rose than musk and vice versa, but most people get both main components. One person wrote, however, that she gets all rose and no musk or any other basenotes at all, and another person wrote that she got all musk and zero rose. I’m guessing the people at the outer extremes like that must either be so sensitive to some ingredients they do smell in the scent that they’re not registering the others, or else they are at least partially anosmic to the ones they can’t smell.

Reviews of Andy Tauer’s new Vetiver Dance are interesting because some people say they don’t get any lily of the valley at all and others say it dominates all else on them. I’m in the middle ground because I smell a distinct and fairly strong lily of the valley note but not dominant over the rest of the scent, and I suspect most people fall into that general range. Whether people like the lily of the valley note is a different question than whether they perceive it to be there; when you read reviews of any scent, you’ll see differences both in opinion and in perception (and some, but not all, of the differences in perception will be due to the scent actually smelling a little different on different people).

One person couldn’t smell any smoke in Fireside Intense, and that is her own scent truth even though it’s surprising to others who smell lots of smoke. Perhaps she is so sensitive to something else in the blend that it wipes out her ability to smell the smoke. It’d be interesting to have her smell some of the ingredients to pinpoint what’s going on and how the scent could be altered to remove the ingredient that gets in the way for her (anosmia seems less like the culprit here because Fireside Intense has so many smoky ingredients it seems unlikely to be anosmic to all of them). I wonder if these sensitivities happen in the nose, or more likely farther up the pathway and maybe in the brain’s perception of scent? I don’t know enough about the science of smell perception to explain the differences I see, but I know they are real and sometimes large.

I have a dear friend who can detect a drop of rose or sandalwood from a mile away, lol, so she needs those notes to be very subtle or they feel overwhelming (yes, you know who you are if you’re reading!). Others can be sensitive to cedar or musk or a certain spice and it’s not that they dislike the note, but they just need it to be very subtle. I suppose you could say that’s a preference, but it’s because they are so sensitive to some notes that those notes loom over all others if they are too strong, and often what they consider too strong is a level considered yummy by many others.

When presented with an isolated aroma chemical or a perfume with a high amount of that chemical, people will have lots of common ground but major differences too. With ISO E Super, for example, some find it woodsy/cedary/ambery and very pleasant, some find it mildly unpleasant and sour, some smell vinegar or pickles, and some are anosmic to it or find it comes and goes. Another interesting example is the aroma chem methyl laitone, which is a creamy, milky, lactonic ingredient often used to soften sandalwood or white floral accords. Most people get a note of coconut from it, though not the same as coconut aldehyde. Some people are very sensitive to the coconut note and get very strong coconut even when it is used in tiny dilution in a blend, and at the other extreme some people just sense a creaminess and smell no coconut whether sniffing it in isolation or in a blend.

The upshot of all this for me is to be aware of and tolerant of our differences. Remember when you sniff or review something that your experience is just as valid as anyone else’s, but that other people may differ greatly in how they experience the same scent and their scent truth is just as real to them as yours is to you. Sometimes our tastes change with time and we come to appreciate things we didn’t like before, but some of our basic sensitivities, anosmias, and preferences will probably remain fairly steady over time.

This post isn’t meant to be very scientific, but meant just to state some observations I’ve made while working on scents. Dr. Luca Turin may have explanations for the differences we experience in perception of scents, though he may have focused more on the similarities in how we smell scents because that’s more relevant to the basic mechanics of scent perception that operate in us all, and because it is probably more important overall than our quirky differences.

There must be a fair amount of agreement in what we smell in order for perfumes to seem pretty much the same to many of us; for example, most of us perceive something like Coco as rich, warm, and spicy. But when you get into the deeper details people start to differ not just in preference but in perception too, and at least some of this individual variation seems to come from people’s different sensitivities to various ingredients, making some notes stand out to them more than others and sometimes even totally masking lighter notes.

Maybe I’ll come to understand all this better as I keep working and learning, but the topic is fascinating to me. Keeping ingredient sensitivities in mind helps me understand the variety of reactions I get from scent testers and helps me customize perfumes for people (I’ve not had time to do custom blends this year but really want to get back to it eventually).