By Meghan Daum

updated 8:44 a.m. ET July 11, 2008

Sexiness, like love or nostalgia or sinus congestion on a pollen-free day, has a way of sneaking up on us at the most improbable moments.

How do we account, for example, for that ineluctable feeling of desirability that can come over us when we are traipsing home from the yoga studio in sweaty leggings and flip-flops that reveal more about our pedicure history than we'd like? And how, by the same token, do we explain the ease with which many of us can slip into our most reliably fabulous Balenciaga dress and Louboutin slides and still feel as sexy as a bag of carrots?

There are, of course, as many reasons for this cruel dichotomy as there are ways to feel bad about ourselves.

We can blame hormones, headaches, pimples, bloating, bad moods, bad hair, or bad lighting. We must also consider what it is we're staring into. Mirrors, as all women know, are highly politicized entities. For reasons that I am convinced are more complicated than national health care, it is entirely possible for me to look and feel reasonably hot in front of my own mirror and, less than an hour later, catch a reflection of myself that suggests some shapeless creature from Jim Henson's workshop has borrowed my outfit and copied my hairstyle, and is blithely chatting up my friends, all of whom are too polite to say anything.

There have, of course, been times when I have felt almost unbearably sexy for no apparent or justifiable reason: retrieving the newspaper in pajamas and clogs, standing over the kitchen sink washing dishes, pondering the produce selection at Whole Foods. None of these occasions led to or had anything to do with an actual sex act.

In other words, let's get one thing very clear: The phenomenon I'm discussing has to do with sexiness, not horniness. There is a sizable, if nuanced, distinction. If this were the analogy portion of the SAT, we might say that sexiness is to horniness as epicureanism is to hunger. Whereas lust tends to limit its reach to particular people or stretches of time (and, like hunger, can presumably be sated via fairly standard channels), sexiness is a state of mind. It is inextricably linked to sex as a concept but wholly separate from fornication. Despite our preoccupation with the sexiness of women, sexiness applies to both genders. Despite the youth-centric tyranny of our times, it transcends age. As much about posture and voice intonation as it is about cleavage or skirt length or the dimensions of our posteriors, feeling sexy is, at its root, about owning ourselves. It's being at home in our own skins. No wonder it is so damn elusive.

Hot-headed "The big, teased hyper-Barbie thing just isn't sexy anymore," says hairstylist Orlando Pita, owner of the Orlo Salon in New York City, "and we're breaking away from all the extensions." Naturally long hair that hits somewhere between the shoulder blades and the midback and is "a little undone" is most appealing now, Pita says. The sexiest cut is soft, feminine long hair, with layers angled around the face, says hairstylist Eliút Rivera, owner of Salon Eliút Rivera in New York City — "otherwise it looks like a curtain." Hairstylist Guido suggests making the look sultrier with sideswept bangs. When styling, aim for goddess waves that are pretty but still sophisticated. To help you get that lushness, Pita says, blow-dry with a large-barrel brush for curly hair, or a smaller-barrel brush for straighter hair. — Lindsy Van Gelder

After all, pretty much anyone can have sex.

Capturing the essence of sex and customizing it to our own needs and tastes is more difficult. Hence, another analogy: Having sex is to being sexy what conceiving a child is to raising a child. The first, age and health permitting, is more or less a biological function. The second is an art: a complicated, ever-evolving process that no two people can possibly do the same way. And just as the parents who are most successful at child rearing are often those who pay the least attention to its fads (heated diaper wipes) and socially constructed paranoias (the idea that the child will suffer due to unheated diaper wipes), women who possess an innate eroticism tend to do the least amount of worrying about how they measure up to popular images of sexiness.

The Unlikely Hot Girl
Enter the Unlikely Hot Girl. We all know at least one of her, more likely several. She's the less than totally attractive woman who mysteriously draws men to her as though she were the last female on a remote tropical island. In other words, men don't simply like her, they want and need her; they require her. It's not that she's ugly. She's just notably imperfect. Maybe she has crooked teeth or substantial hips or a bump on her nose. Maybe her breasts are too small or saggy or possessed of any of the myriad flaws that, here in the Plasticine Age, are avoided only by way of artificial mammary enhancement. Maybe the worst thing we can say about her is that she's not as attractive as we like to think we ourselves are. So why is she being madly pursued by the guy we've met several times but who never remembers our name?

Welcome gestures You don't need to initiate strip poker to be the sexiest girl in the room. Body language is a simple way to convey sexiness. "Self-assurance is the key to projecting attractiveness," says Beverly B. Palmer, professor of psychology at California State University–Dominguez Hills. Make eye contact. "A quick glance communicates interest," Palmer says; "a lingering look moves it a step further." In fact, an independent study found that prolonged eye contact is one of the most successful tactics to initiate flirting. Touch your clothes. Adjusting your necklace or smoothing the hemline of your skirt leads the eye to the feminine parts of your body without being vulgar. Be on your toes. At a party, staying on your feet makes you look confident. "Don't allow yourself to be visually lower than everyone else," Palmer advises. "We all pay attention to someone who's higher up." Don't be cross. Crossing your ankles and folding your arms says "stay away." Lean forward while talking, and leave your arms at your sides. "Open posture says you welcome interaction," says Palmer. "People like to feel wanted." — Hannah Morrill

Conventional wisdom might say, "It's the pheromones, stupid!" Most often associated with insects and those intriguing advertisements in the backs of magazines — "Attract the Mate You Want: Order Now!" — pheromones are chemicals that trigger a variety of biological responses. There are pheromones associated with danger from a predator, with the marking of a trail, and with claiming territory. In other words, pheromones are the chemicals released when bees sting, when ants travel to and from their nests, and when dogs urinate on everything they pass.

Notice that none of these examples involve people being asked for their phone numbers in bars. That's because despite the widespread assumption that pheromones are inextricably linked to erotic appeal, there’s a long-standing debate as to whether humans even have them. (William Shatner has said, "I'm told that my pheromone count is very high and that I am just naturally attractive to women and, I think, sexual deviants.")

"The whole notion of human pheromones was a popular thing with psychiatrists in the 1970s," says Mary Roach, author of "Bonk: The Curious Coupling of Science and Sex" (W. W. Norton), which looks at the elaborate lengths researchers have gone to in order to untangle the mysteries of Eros. "But increasingly it looks like a nuts-and-bolts chemical thing. It has to do with the insect world."

Still, as Roach describes in "Bonk," the idea that a human sex hormone can be identified and isolated (and even packaged and sold) has long captured the scientific imagination. In 1971, University of Chicago psychologist Martha McClintock, then a Wellesley College undergraduate, published research suggesting that, thanks to pheromones, women who lived in groups tended to get their periods at the same time each month. That same year, Richard P. Michael, a British behavioral neuroendocrinologist studying rhesus monkeys, professed to have isolated whatever compounds in vaginal secretions cause male monkeys to initiate sex when they sniff them. The assumption was that, due to genetic similarities between primates and humans, the existence of monkey pheromones must prove the existence of human pheromones. Unfortunately, in 1977, when a sample group of married women were asked to apply synthetic rhesus monkey hormones on their chests at bedtime for three months in a row, they reported no change in their husbands' interest level or behavior.

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