Rachel Herz, PhD is a well-known psychologist studying smell and flavor. In addition, she writes general-interest books on the topics, and the unique perspective of her work has done a lot to bring awareness of this fascinating field to the broader public.
This interview was conducted in the summer of 2019.
RM: Can you describe your professional activities these days?
RH: I’m a freelancer, I guess, an amalgam of research at Brown University and teaching at Boston College, plus commercial projects through RSH Enterprises. I also work on grant funded studies with collaborators at various other universities and at the beginning of my professional career I was on the faculty of the Monell Chemical Senses Center. I also do expert witness work, often for people who have lost their sense of smell from injuries, but also on “nuisance odor” cases, where I try to explain what is going on when people say they smell the malodors they’re reporting. .
I’m currently working on a children’s version of Why We Eat What We Eat which I hope will encourage children to play a more active role in their food world, and I’m a co-author of a textbook on sensory science and perception.
RM: It seems that chemosensory science is accelerating these days. Are we getting close to understanding everything? I know, kind of facetious question.
RH: There’s actually still fundamental disagreements and even confusion about exactly how we perceive smell. For example, there still isn’t agreement or a full understanding of how smell works from being purely chemical to the point where it becomes a neural code and acquires meaning, when the brain lights up with: ‘Oh, this is what I’m smelling.’ It’s not clear how all this happens. Vision is comparatively simple compared to olfaction—our sense of smell. Taste is a simple system, but our sense of smell serves many functions and is incredibly complex in the way it works in the brain.
There are also some problems with the balance of what scientists are researching. Since Linda Buck and Richard Axel published their paper revealing the structure of olfactory receptors in 1992, lots of people went into olfactory research, and as a result the tilt has been more to the molecular side, and less behavioral. Psychological research on the sense of smell isn’t as well respected overall. In part because it appears less rigorous than the biochemical and molecular work, and unfortunately because where real human smelling is involved some of the old puritanical values that it shouldn’t be studied too much since it is a lower sense compared to vision still hold.
There are so many interesting things that olfaction does besides detecting chemicals. For example, there’s good evidence that an important function of olfaction is navigation. And it’s also really involved in social behavior. There’s a recent study where they found that when we meet people and shake hands, we usually sneak a sniff of our fingers afterwards. They have videos of this behavior, and the people doing it are completely unaware.
RM: It seems a little odd, since the psychological work should be where the money is, at least in terms of figuring out and changing behavior, from a food and drinks, consumer products and also with health outcomes. But a lot of this practical psychological work is proprietary, done for consumer products companies.
RH: Yes, we did this study with various scents of hand lotion, where we showed not only there was a preference for the most pleasant scents, but that those products were perceived as performing better as well. It’s a combination of the sensory experience, the psychology and the environment that all determine our relationship with aroma.
RM: From your writing and research, you come down pretty strongly on the side of learning as far as like or dislike of any particular aromas, with very little of that hedonic quality genetically determined (in contrast to taste). Is that correct?
RH: It’s complicated, but my general sense is that we are complete blank slates for olfaction, as far as like and dislike. They’ve waved Q-Tips with aroma chemicals under the noses of infants and get a wide range of reactions, from glee to disgust, with positive reactions to things like butryic acid [usually described as vomit or sweaty socks], where with a taste like bitter, there is a clear negative reaction and a disgusted facial expression.
You have to remember, our olfactory system is operational by the end of the first trimester, so we are exposed to our future food in the womb. Once we’re born all it takes is a single encounter in a positive or negative context to attach a hedonic association to an aroma, so it builds up quickly, and our lives have a trail of emotional labels attached to various odors.
If you think about it from an evolutionary standpoint, it makes sense. We are generalists and can exploit any habitat on earth. Therefore we need to learn what the chemicals in the environment that we’re in mean. The same smell in one locale could mean nutritious food and in another environment mean poison. So it wouldn’t make work to be born hardwired to respond to in specific ways to smells.
RM: Having spent much of my career as a visual artist, I’m fascinated by the idea of a semantic structure—an organizing principle of aroma—a “rainbow” in a way, What are your thoughts on that?
RH: There have been a number of researchers, going back quite a while, who have attempted to come up with aroma “primaries”, with not a lot of success. Even if it’s possible, it’s probably not going to be the same primary aromas for everyone. With vision [unless you are color-blind], red is red which is mostly maybe experienced similarly for most of us. But with aromas, we just don’t perceive them the same way for many reasons. In fact, genetically speaking, each of us has a unique array of receptors expressed that detect scents—so each of us has a unique nose.
In a professional situation like cuisine, wine or beer, it’s very useful to have a common understanding so you can work together, such as the wine wheel, and a colleague and I have developed a kit called “the educated palate” for culinary enthusiasts. But there haven’t been many teaching tools for the general public..
RM: Because aroma perception is so loaded with emotion, do you see those emotions and attached memories as a helpful tool for people who want to be serious tasters?
RH: This can be a useful first step, as in “do you like what you are sniffing, and why?” When you recognize the emotions, associations and memories that are attached to various odors that can help you remember the odors and categorize them in terms of their meaning for you.
RM: How easily are people’s reactions to aroma changed by language? Is this a good thing, and for who? If you want to resist, can you?
RH: It’s extremely easy to change people’s response to odors with words. We did an experiment where we had people smell something [butyric acid] and in one case we called it “vomit” and in another instance “parmesan cheese” and people had totally opposite reactions to the scent and wouldn’t believe that they were smelling the same aroma both times. We created an odor illusion with a word!
When it comes to pleasurable experiences I don’t think it’s good to have too many words involved because words can literally “overshadow” your sensory experience. If you’re drinking a wine, or beer, you really like and start thinking of all the descriptors to define it, you lose the pleasure of the drink as a whole.
RM: While we mostly think of olfaction as an experienced sense, it’s clear that some pathways end at less than fully conscious perception, yet they can drive behavior, as experiments with sweaty t-shirts have shown. How do you think it works in humans?
RH: There’s a big difference between pheromones and someone’s actual body odor. Recent scientific work has debunked any existence of pheromone effects in humans. However, we can respond in real ways to the body odor of someone and body odor can communicate a lot of messages. For example, we can recognize the scent of fear in someone else people and we can be turned on and off by how a person smells.
RM: What does that mean for “smell dating?”
RH: Women in particular are very affected by how someone of the opposite sex smells in terms of being attracted or turned off. But rather than it being some innate mechanism, it seems that we are just avoiding the smell of our own family—like a scent based incest avoidance mechanism. There was a study with female rats and male littermates who were switched at birth with unrelated males, who then grew up with the females. When it came time to choose a mate, the females preferred the males who were their real brothers that they hadn’t been raised with over the unrelated males that they had grown up. This is pretty strong evidence for mate choice being based on learning who’s who rather than some innate reaction to the smell.
RM: Why do flowers smell so good to us? It’s easy to see why bees care, but what’s the attraction to humans?
RH: There are some floral aromas in foods, but I think it’s pretty much a matter of what’s in your landscape and the feelings you develop starting early in life. In Latin America, musks are common fragrances in cleaning products, but in North America here they’re seen as a really sensual note in perfumes. In the UK, the wintergreen flavor in candy [and root beer] is used in toilet cleaners. So the meaning and emotional value of many odors is totally arbitrary. I wonder as we become more globalized, if this will flatten the landscape and we’ll lose some of the cultural diversity in our scent universe.
RM: What does paying attention to the aromas around you really mean as far as appreciating life? Anything about your own life that has changed as a result of your work and understanding our chemosensory selves?
For me the big lesson is just how important it is to pay attention to the scents around us. Focusing on your chemosensory world just makes life more enjoyable. It can also lead to a happier and healthier relationship with food. If you can slow down and have time to think ‘How great is this?’ and feel the neural excitement that flavor creates then you’ll get more pleasure, satisfaction and satiation from what you’re consuming. At the same time when you pay to attention to what you’re eating you may realize that after the fifth or sixth bite that chocolate or pizza isn’t giving you the same bang for your buck, and it stops being worth eating (unless of course you’re starving). When it comes to dieting, the worst thing you can do is restrict yourself and make something off-limits, because that just makes you want it more. Eat what you like as long as it truly feels good, and ask yourself: ‘Do I really want to eat another bite?’
Rachel Herz, PhD is the author of The Scent of Desire, Why You Eat What You Eat and more.