The Female Nose Knows Best

I owe my ex-husband an apology. He’ll be surprised to read this--and even more surprised to hear why I’m sorry. Not for the fights over washing the dishes or who wanted to make love and when. No, this has to do with something I never even suspected was a problem. It has to do with smell.

That’s right. Behind the Household Tasks Wars and the Sex Wars, it seems, there was a less obvious conflict: the Smell Wars. Then, it was no big deal. I just got a little ticked off each time he’d open the refrigerator, pull out a carton of milk with an expired-date stamp or a container of leftover Chinese food and say, “Here, you smell this stuff.”

Naturally, I protested. He’d swear that his sense of smell wasn’t good enough to tell whether these suspicious items were spoiled--which, frankly, always sounded to me like someone who just didn’t want a snoot full of sour milk.

Well, I was wrong. The fact that I could tell from a meter away that the milk was now cheese did not mean that my ex could do likewise. It turns out I really do have a better sense of smell than he does. And not just me. In all human cultures, women are able to sniff more reliably than men. That is, they can detect odors in lower concentrations, identify them more accurately and remember them longer than men.

Now, to many people this may not seem earth-shattering. Men and women have many differences, such as anatomy, childbearing and the ability to parallel park. What real-life difference can our sensitivity to smell possibly make?

Lots, according to Richard L. Doty, director of the Smell and Taste Center at the University of Pennsylvania and the inventor of a widely used standardized smell-sensitivity test. In a landmark study published in 1984, Doty tested the olfaction of 1,900 subjects whose ages ranged from 4 to 100. Using what scientists call a “microencapsulated odor test”--basically a rigorous version of scratch and sniff--he found that females of all ages were able to identify odors more accurately than males.

“Women have a better sense of smell, period,” Doty says. Although the gap is not large until old age, Doty has found that it can be troubling to a mate whose olfactory experience is more acute than her husband’s. “Wives sometimes come in complaining that there’s something wrong because their husbands don’t seem to appreciate the same smells they do. When we test the men, they’re normal relative to their peers. The problem is that women live in a somewhat different world, smell-wise.”

What makes things confusing (and sometimes infuriating) is that seen--or rather, smelled--from the outside, it seems as though women and men live in exactly the same world. We inhale the same odors, which means the same air laden with the same odor molecules. These molecules go to the same place, namely the mucus lining at the tops of our noses. There, they are transported to millions of receptor cells in the membrane lining; the receptor cells are designed to bond with the odor molecules and produce corresponding electrical signals. Those signals travel along a corridor of nerve fibers to the limbic system, which is located in the same part of the brain involved in memory and emotion.

So far, so good. It’s what happens next that may separate the women from the men, says David Zald, a research fellow at the Veterans Affairs Medical Center in Minneapolis and at the University of Minnesota Medical School, who has studied how the brain processes emotional stimuli. When his colleague, Dr. Jose Pardo, asked male and female subjects to think sad thoughts--that is, to engage the part of the brain where smells register--both sides of the women’s brains were activated while only one side of the men’s brains was engaged. The researchers believe that women and men may also differ in the parts of the brain they use during smell-related tasks--a hypothesis that the scientists are preparing to test in further studies to be conducted later this year.

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Whatever the reason, females and males are in different smell worlds from birth. When Gary Beauchamp, a biologist at the Monell Chemical Senses Center in Philadelphia, gave 4- to-6-month-old infants a rattle infused with an odor and one that was odor-free, the girls paid more attention to the odorized rattle than the boys did. Other researchers have found that infant girls can identify breast pads worn by their mothers with greater accuracy than boys can. This last is a skill that cuts both ways, for mothers can pick out T-shirts worn by their newborns from those worn by other babies, a feat even the most dedicated new fathers can’t perform.

Scientists are still scratching their heads over why this is so. Charles J. Wycsocki, a neuroscientist at Monell, hypothesizes that because humans can detect odors circulating through their own bloodstreams, mother and fetus may exchange smells during pregnancy that help them identify each other after birth occurs. This does not explain, though, why female babies are so much better at doing so than male babies.

Nor does it explain why this basic difference increases with age. According to Doty, both men and women peak on odor-identification tests in their teens and remain relatively level until their 60s, when olfactory abilities drop off. But men tend to lose their sense of smell at an earlier age and to a larger degree. Doty suggests that the reason may be that estrogen and, later, estrogen replacement therapy provide some degree of protection for women’s nasal membranes.

But as with so much about our sense of smell, no one knows for sure. Indeed, compared with what we know of other human senses such as sight and hearing, our knowledge of smell is rudimentary. One reason may be that smell is a purely chemical sense and difficult to quantify. Compared with what we know about color and sound, which can be measured in terms of wavelengths of light and audio frequencies, there is no obvious dimension along which to measure smells.

Then, too, we have few words for smell. Considering that the brain’s smell center is far removed from the main area that processes language, it’s not surprising that we find it hard to describe even quite familiar smells, although we inhale and exhale more than 20,000 times a day. Think, for example, of how little specific information we derive from adjectives such as “pleasant” or “fresh” or even “pungent,” or any of the words we commonly use for smells.

Women can name smells more precisely than men can, and throughout evolution they’ve had a perceptual advantage. Why? Back when one-celled amoebas ruled the Earth, being able to detect chemicals in the environment was critical. But as life forms became more complex and this kind of crude detection developed into olfaction, smell became incorporated into every function of life, including reproduction.

So it happened that, in certain species, when females ovulated or were in estrus, they gave off unmistakable odors that powerfully attracted males. Of course, this led to maximum reproduction, so natural selection favored those who displayed it, including our remote mammalian ancestors.

But humans are different. As we came to rely ever more on higher brain functions such as language, we used smell far less than did other mammals. In particular, we did not use it for reproduction. Rather than announcing ovulation with either smell or visual cues, humans began hiding the news--a fateful change, according to Australian zoologist D. Michael Stoddart. Indeed, Stoddart suggests in his book, “The Scented Age,” it was this abandonment of what had amounted to the advertisement of estrus, more than any other single adaptation, that predestined human evolution to take the course it has followed.

With estrus hidden, Stoddart suggests, it became possible for humans to maintain the social cooperation necessary to hunt large game and, eventually, to develop settled communities. Hidden estrus also allowed men and women to form the monogamous units needed to raise offspring whose advanced brains took so long to reach maturity. For men and women to have the best shot at reproducing their genes, they would have to cooperate for many years--a commitment of time and energy that required, among other things, that each be able to rely on the other.

According to Stoddart, the solution--what he calls “the privatization of sex”--was both simple and profound. Women evolved the capacity to be sexually receptive throughout their cycle, which meant that there was no need to broadcast through smell any particular window of opportunity. In turn, men developed constant readiness for sex. Perhaps as a reward for monogamous behavior, sex became pleasurable rather than a reflexive response to odor cues--a development that zoologist Desmond Morris summarizes in “The Naked Ape” (Dell, 1980) with his famous aphorism, “Sex became sexier.”

Still more changes were in store. In most cultures, if not all, the smell of women’s genitals not only ceased to communicate biological information, but came to be considered unpleasant. What had been a turn-on became a turnoff. Stoddart speculates that such a series of events may have been necessary to keep men’s sexuality in check and to promote general social stability. Whatever the cause, mammals began to want to smell like something other than themselves.

Throughout recorded history, that something is likely to contain sexual secretions from other species. Common ingredients for perfume, for example, include musk taken from deer in rutting season, anal gland secretions of sexually active beavers and civet cats, and even plant odors designed to resemble insect sex attractants.

Perhaps it’s just coincidence, but it’s the way we humans have managed to have our olfactory cake and eat it, too. With just a dab of perfume, a whiff of cologne or a waft of incense, we can be what Stoddart calls “gently aroused”--able to have a pleasant smell experience but hang on to the essential social arrangements required for the human species to survive.

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Estrus aside, though, smell remains a vital component of our romantic lives. The reason is that each person has a unique odor, a combination of hundreds of smell molecules reflecting everything from diet, ethnic background and brand of shampoo to exactly which bacteria are present in the intestines. Although we may not be consciously aware of any other person’s odor print, it plays a significant role in our relationships.

“When couples don’t like each other’s odor, it’s hopeless,” says Susan Schiffman, a professor of medical psychology at Duke University Medical Center. Try as you might, she says, you can’t overrule your gut responses. “If you don’t like his smell at the beginning,” she says, “you won’t ever like it. In fact, it will just keep getting worse. The only thing you can do is be sure beforehand.”

That’s especially true for women. According to Rachel Herz, a Monell psychologist, women are more sensitive than men to smell when choosing a lover and during sex.

“Visual information--seeing each other across a crowded room, that sort of thing--comes first,” Herz says. “It’s the most important variable for men all the way through. But for women, when it comes down to whether to have sex with a specific person, odor is more important than anything else, including how he looks, how his skin feels or the sound of his voice.” She explains that smell works “in the negative,” meaning that a woman may not be attracted to a man who smells good to her, but she can easily be turned off by one who doesn’t.

Although no one knows for sure, this may be a holdover from prehominid days, when females used smell to tell them whether a potential mate was healthy. One persuasive bit of evidence is that women’s sense of smell is still most acute during ovulation, which happens to be precisely when they are most in need of accurate information about the physical well-being of possible fathers for their offspring.

Of course, most women no longer rely on their noses to determine whether a man is in good shape. Indeed, the thought that our remote foremothers once did so is a powerful reminder of how different our lives are now, and how large have been the physical and sensory trade-offs made during the course of human evolution. We no longer sleep at least half the day, we eat fast food, and we couldn’t survive living outdoors. Presumably, being present today--at the cutting edge of all human existence to date--is worth it. And even if it isn’t, we have little choice in the matter. We can’t turn back into early hominids.

Fortunately, at least as far as our noses are concerned, we don’t have to. Among women, the sense of smell is alive and well. In the midst of our high-tech civilization, we continue to live in a sensory environment, and we are still able to take in and be influenced by thousands of odor molecules all day long. If, now and then, we can slow down enough to breathe deeply and savor the thousands of different scents we are inhaling, we can give ourselves at least a little bit of what has been left behind.

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Gwenda Blair is a contributing editor at SELF, where this article first appeared.

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How Sense of Smell Works

Most people can distinguish thousands of different odors, whether foul or fragrant, with a simple sniff of the nose. For people without a sense of smell, food doesn’t taste as good, flowers and perfume evoke no special memories, and potential hazards signaled by noxious odors fo unnoticed.

1. Airborne molecules of garlic travel through nasal passages.

2. Molecules dissolve in mucous membrane.

3. Receptor cells are stimulated, then generate nerve impulses.

4. Nerve impulses travel through olfactory nerve to the olfactory bulb.

5. Olfactory bulb analyzes impulses and sends them to brain, which identifies the smell.