The smell of love, part three

Why do some people smell better to you? A look at how human body odor influences sexual attraction.

The great pheromone hunt
For an animal whose nose supposedly plays no role in sexual attraction or social life, human emotions are strongly moved by smells. And we appear to be profoundly overequipped with smell-producing hardware for what little sniffing we have been thought to be up to. Human sweat, urine, breath, saliva, breast milk, skin oils, and sexual secretions all contain scent-communicating chemical compounds. Zoologist Michael Stoddart, author of The Scented Ape (Cambridge University Press, 1991), points out that humans possess denser skin concentrations of scent glands than almost any other mammal. This makes little sense until one abandons the myth that humans pay little attention to the fragrant or the rancid in their day-to-day lives.

Part of the confusion may be due to the fact that not all smells register in our conscious minds. When those telltale scents were introduced to the VNO of human subjects, they didn't report smelling anything -- but nevertheless demonstrated subtle changes in mood.

What could be a source of what might be our very own pheromone?

Humans possess three major types of skin glands -- sebaceous glands, eccrine (or sweat) glands, and apocrine glands. Sebaceous glands are most common on the face and forehead but occur around all of the body's openings, including eyelids, ears, nostrils, lips, and nipples. This placement is particularly handy, as the secretions of these glands kill potentially dangerous microorganisms. They also contain fats that keep skin supple and waterproof and, on the downside, cause acne. Little is known, however, about how sebaceous glands contribute to human body odor.

The sweat glands exude water and salt and are non-odorous in healthy people. That leaves the third potential source of a human pheromone -- the apocrine gland. Apocrine glands hold special promise as the source of smells that might affect interpersonal interactions. They do not serve any temperature-managing functions in people, as they do in other animals. They occur in dense concentrations on hands, cheeks, scalp, breast areolas, and wherever we possess body hair -- and are only functional after puberty, when we begin searching for mates.

Men's apocrine glands are larger than women's, and they secrete most actively during times of nervousness or excitement. Waiting colonies of bacteria turn apocrine secretions into the noxious fumes that keep deodorant makers in business. Hair provides surface area from which apocrine smells can diffuse -- part of the reason why hairier men smell particularly pungent. (Is it any coincidence that hair at the arm pit and the genitals sprouts at puberty, when apocrine glands start producing food for our skin bacteria?)

Most promising of all, apocrine glands exude odorous steroids known to sexual behavior in other mammals. Androsterone -- a steroid related to the one that nearly doomed the hapless musk deer -- is one such substance. Men secrete more androsterone than women do, and most men become unable to detect the stuff right around the time they start producing it themselves -- at puberty.

In 1986, the National Geographic Society organized the World Smell Survey to investigate whether people from all cultures experience odor in the same fashion. They distributed over a million scratch-and-sniff cards and questionnaires about subjects' detection and perceptions of intensity of smells, from banana to the sulfur compounds added to natural gas as a warning agent. Included in the survey was the scent of human androsterone.

The steroid itself is not pleasant to smell. Worldwide, those who could smell it rated it second to last in pleasantness -- just ahead of the sulfur compounds put in natural gas. A foul-smelling pheromone? It's hardly what scientists expected to find.