MAUREEN CAVANAUGH (Host): As Valentine's Day approaches, we're seeing big red hearts everywhere, on gift cards, store decorations and the shapes of candy boxes. Of course, the hearts symbolize love and romance. But if we wanted an accurate symbol of what sparks love and romance, we might want to put up a big picture of a nose. I don't know how well a nose-shaped candy box would go over but it's a scientific fact that scent plays an enormous role in romantic attraction. And just in time for Valentine's Day, we have a guest to tell us about what the nose knows about love. I’d like to welcome my guest Rachel Herz. She’s the author of “The Scent of Desire.” Rachel, welcome to These Days.
DR. RACHEL HERZ (Author): Thank you, Maureen. Good to be here.
CAVANAUGH: Well, does desire smell the same for everyone?
DR. HERZ: No, it doesn’t. And actually your comment about something so important for attraction is two things, first of all we think of scent, you know, creating sensual moods and so forth and food aromas, and then there’s the issue of body odor and that’s where things get down and dirty, as it were…
CAVANAUGH: Aha.
DR. HERZ: …when it comes to actual sexual interest. And it’s especially important for women, how a man smells.
CAVANAUGH: That’s remarkable. Now, what scents do we traditionally link to romance?
DR. HERZ: Well, I think in our culture the scent is really the by product of the food source. For example, it’s often the case that chocolate and so on, figs, other kinds of sort of sensual foods are linked to romance. Interestingly, also we tend to link the scent of musks to romance, too, but what’s quite important here is that the responses we have to smells are all learned. They’re not innate, they’re not intrinsic to produce any particular response because the scent of musk in South America is actually the scent of cleaning products. So in South America, you would not be thinking lingerie, you would be thinking mop if you smelled musk.
CAVANAUGH: Do we have any idea, Rachel, how these scents become part – become linked to certain emotions?
DR. HERZ: Yes, and it’s through this concept of association. So as a function of the experience you’ve had with a scent in your past or how you’ve culturally come to learn the scent, you will have that association to it. But that is important because you may not have the same association as your culture for your own idiosyncratic reasons.
CAVANAUGH: And when you were talking about, you know, we have flowers and chocolates and then those deeper scents that we’re attracted to, is there – From what I understand, there is a difference – there is a controversy over whether humans emit pheromones. Tell us a little bit about what pheromones are.
DR. HERZ: Well, pheromones are a chemical that may or may not be smelled and they’re used for communication purposes. Actually, they were first discovered by investigating the social insects. And so the humans’ connection is a little bit of a stretch. And the reason why everyone has been searching for the idea of pheromones in humans is because in mammals they’re often used in reproductive behavior. So to, for instance, get into the position necessary for reproduction and so forth, a female has to be exposed to a particular pheromone and so on. Now, in humans there really is not any evidence that we are specifically affected by these chemicals in any kind of way other than potentially menstrual synchrony. But there is a possibility that a certain chemical that’s identified as androstadienone, which may be a kind of a pheromone, it is actually a pheromone for pigs, and it is also present in human sweat, and it may have a modulating effect on mood for women. But this is not very, you know, strongly shown. The point is that pheromones, if they’re acting at all, have a weak effect from a sexual perspective but real body odor, what you can actually smell, so the idea of pheromones is you don’t have to smell anything. But actual smells coming from the body definitely do have an effect, especially for women.
CAVANAUGH: And do we know why certain people smell better to us than others?
DR. HERZ: Yes, as a matter of fact, and it has to do with the biology of body odor and the scent of a man that we women will find particularly attractive is from a man whose, actually, immune system is more different from ours than more similar. So and why this is important is that from the point of view of mating, we want to mix our genes with someone who is going to give us the healthiest child possible. And so, therefore, if you mix your genes with someone who is more different from you, you’re going to end up with more possible protection from illness and less likelihood of doubling up on anything bad you might have. So it turns out that the scent of your body is actually the external representation of your immune system genes and we all smell unique. Not a single other person on the planet, unless you have an identical twin who’s eating the exact same thing as you, smells like you. So it’s like your fingerprint. And we find, women in particular, the smell of men who are more different from us genetically as smelling sexier and more pleasant to us.
CAVANAUGH: I’m speaking with Rachel Herz. She is the author of “The Scent of Desire.” Now, Rachel, I wonder, you know, couples break up so do we get tired of each other’s smells after a while?
DR. HERZ: We can. The other thing that can happen actually, interestingly enough, is birth control pills affect how women respond to the scent of a man. And what’s been found in studies where women have either been on or off the pill is that women on the pill, in fact, make a biological mistake. They actually find sexier and more pleasant smelling men who are more similar to them genetically and the idea behind this is because that under a state of pregnancy, which hormonally the birth control pill mimics, you want to be around family and kin and so forth for protection. And this may be why women are choosing the sort of more similar, genetically speaking, men as being more pleasant. Now what can possibly happen over the course of a relationship is that, for instance, if a woman started on the pill and then goes off the pill, her man may now smell different to her and that could influence how she’s feeling about him. It could also be the case that now she’s not so crazy about him and now she smells him as being somewhat different and now this new smell she’s getting from him is connected to ‘I can’t stand you anymore’ and, therefore, his smell becomes really aversive. And if there’s one thing that’s going to stop intimacy, it is smell. You cannot get over that barrier, as a woman in any case. You know, if he just – if he smells wrong or bad to you, sexual behavior is unlikely to occur.
CAVANAUGH: Well, for Valentine’s Day, you know, a big item is usually cologne and perfume. What role does this play in attraction?
DR. HERZ: Well, it actually plays a very big role and a kind of a sneaky role, too, because if a woman really likes how a man smells, it really doesn’t matter whether it comes from his real body odor or his fragrance. So if a man is wearing a fragrance that a woman really likes, she will be very attracted to him. And actually what I’ve found is that above and beyond any other physical feature, so how he looks, the sound of his voice and so forth, and every social feature except for how much of a nice guy he is, how he smells is going to be the number one thing that’ll get her romantically interested in him.
CAVANAUGH: And how is it for men? Is it that they just don’t – they don’t have the power to smell as well as women do?
DR. HERZ: No, I mean, men find that how a woman smells, the scent of a woman important. And in fact, interestingly, a study has just come out showing that men’s testosterone levels actually increase when they’re around or smelling women who are ovulating. But men are actually much more geared towards the visual and so all of the stereotypes are actually true. How she looks is more important to a guy than how she smells.
CAVANAUGH: So I guess it’s probably a good idea for women to give their sweetheart, their husband, a scent they like rather than finding one their husband likes.
DR. HERZ: Exactly. Exactly.
CAVANAUGH: Now, if you could, what is a big mistake that people make about scent?
DR. HERZ: Well, one thing from the point of view of fragrance is wearing too much of it.
CAVANAUGH: Umm-hmm.
DR. HERZ: So this is actually a problem because what happens when we are exposed to a fragrance all the time like the fragrance we wear, we adapt to it. That is to say, we, in fact, stop being able to smell it, which is unfortunate because we don’t get the pleasure of the scent any longer. But other people around us can still smell it perfectly fine and so what tends to happen is people overcompensate for them not being able to smell it and put on way too much so instead of actually other people liking it now, then it becomes aversive because it’s way too strong. So wear a fragrance but don’t wear too much of a fragrance. Even if you feel you can’t smell it, others can, I’d be pretty sure.
CAVANAUGH: Well, this has just been a very enlightening conversation, I must say. Thank you so much, Rachel.
DR. HERZ: Thank you, Maureen.
CAVANAUGH: I’ve been speaking with Rachel Herz, author of “The Scent of Desire.” And you’re listening to These Days on KPBS.
