Pheromones, Immunity, and the End of the Honeymoon

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noseEmotional distance between lovers after orgasmic sex is not unusual. We have suggested that prolactin, a hormone that has many functions in the body, may be a chief culprit. It rises sharply after sexual satiation, and no one knows how long it remains elevated (or continues to surge) as a result.1

2 We think prolactin is possibly associated with post-passion emotional distance because it holds down dopamine, the neurochemical of desire, which, with oxytocin, helps to stimulate sexual activity3 and sustain pair bonds in monogamous rodents (and perhaps humans). When dopamine is low, attraction to a partner may easily suffer because a partner just doesn’t look as good.

Now it appears that another physiological mechanism may also help to create distance between lovers: pheromones. Pheromones are odorless chemicals emitted from the sweat glands. Animals use them to communicate continuously using a special organ in the nose, and there is growing evidence that humans do, too. For example, see this recent article from Scientific American "MIND," Sex and the Secret Nerve (pdf file, 5482k) which discusses a recently-discovered set of cranial nerves that run straight to the centers of the brain that govern mating, and release a powerful sex hormone (GnRH) into the blood. Animals in which these nerves were severed failed to mate, although their sense of smell was unaffected. It is thought that these nerves, which do not run to the olfactory bulb (where smells are processed) play a critical role in sensing pheromones.

In short, when your dog sniffs the air, he is checking both for odors and pheromones, using two different sets of nerves that run side-by-side but apparently have different functions. Both these sets of nerves also exist in the human brain, even though we have lost a part of the brain called the VNO (vomeronasal organ), which helps to process pheromonal signals in animals. Recent experiments reveal that mice respond to some pheromones without a functioning VNO, so perhaps we do, too.

Interestingly, the pheromone-sensitive nerves also exist in whales. Whales still respond enthusiastically to mating signals, even though they no longer have a sense of smell (or a corresponding set of olfactory cranial nerves). Pheromones and this special set of nerves may be the mechanism.

There's more proof that we, too, may be operating on pheromonal messages. Testosterone in male saliva normally increases with exposure to young women, but not with exposure to young men. 4 Clinton's noseIt is believed that exposure to pheromones is the most likely explanation for this finding. In other words, these unrecognized chemicals are subtly controlling subconscious behavior. They appear to give us a healthy boost when we near a potential mate. However, pheromones may also be helping to push us away from a mate.

Certainly they serve this function in cattle and sheep. Bulls and rams show a marked disinterest in sex with females with which they have already mated in a given season, and research shows this is linked to pheromones. Researchers call this phenomenon of moving on to novel partners after sexual satiation "the Coolidge Effect." Researcher James Kohl believes that the Coolidge Effect is extremely likely to be "a function of adaptation to sustained pheromone exposure." In other words, familiarity can indeed breed contempt.

Pheromones may also account for diverse sexual tastes, such as sexual fetishes or a preference for same-sex partners.5 Here's how. Pheromones can interact with hormones, thereby directing our behavior without our conscious awareness. In the research mentioned above, young men's testosterone levels typically increased around young women. However, hormonal responses can be fickle if they become associated with other sensory input from one's social environment. In one experiment an arbitrary odor was deliberately associated with the natural odor of a female. Subsequently this new odor elicited a conditioned male hormonal response 6 even in the absence of the female odor.

Thus, in theory, quite arbitrary associations might cause people to respond sexually (that is, hormonally) in unexpected ways without any conscious action. Fetishes for leather or vinyl could easily evolve, perhaps from something as innocent as masturbating in a closet. Sexual preference could, for some people, evolve through equally arbitrary associations that evoke hormonal responses. Indeed, researcher James Kohl believes that visual and other stimuli will turn out to be far less important in sexual preference than "subtle variations in olfactory/pheromonal input."

7 Research suggests that our hormone and immune systems may be powerful sources of these pheromonal signals. Working together, they appear to urge us strongly toward mates with immunity that is very different from our own — perhaps to help prevent inbreeding and increase the range of immunity in any offspring.8 For example, in one study, women preferred the sweaty T-shirts of men whose immunity differed the most from theirs. 9 sniffing equipment

However, initial preference (being based largely on hormones) doesn't seem to guarantee life-long attraction. As one researcher surmised, the reactions of the T-shirt sniffers are probably "immune reactions that fade across time." So it may be that "even a T-shirt worn by a hunk would generate less interest if the sniffing ladies had to sample that shirt across an extended time."

We wonder if the key event is time, or whether the sniffing ladies' interest might be more likely to shift after sexual satiation with the T-shirt's owner. For us, the tantalizing question is not, "do pheromones initially help us choose sex partners or even their gender?" Quite likely they do. The more interesting question is, does behavior change the pheromonal messages we emit or respond to during the course of a romance? Specifically, does sexual satiation (attempted fertilization) change the pheromonal messages between partners in some cases, much as it does among cattle and sheep?

This is an awkward question to ask, and the answer may be even more awkward. Yet we ask it because of practical experience. There must be some physiological reason that a non-orgasmic approach, like Taoist lovemaking or Karezza, in which orgasm is consciously avoided, leads to greater harmony between partners. Perhaps it "works" precisely because lovemaking without orgasm fails to trigger the typical sexual satiation that alters the pheromonal message between lovers, pushing them apart.

Hormones don't just change in response to our environment; pheromones act as an invisible link between stimuli and hormonal changes. So it makes sense that pheromones may be triggering increased prolactin levels after orgasm. To the extent that this "sexual satiation" message remains elevated, perhaps via pheromonal signals, it may make the ongoing presence of a lover less appealing during the minutes, days or weeks after a passionate encounter. Over time, this unwelcome signal may contribute to bringing the "honeymoon period" to an end.

Our bodies may possess more than one way of encouraging us to move from one partner to another. For example, another possible culprit behind emotional cooling may be the simple conversion of the putative human pheromone androstenol (which registers as musky and pleasant) to androstenone (which registers as urine-like and off-putting). Such changes happen at such a subconscious level that we would have no idea why we feel less interested in a lover. couple in bed

Who knows? Pheromone levels may be affected by how we make love (or by the cues such lovemaking creates, perhaps through greater affection and less goal-driven, selfish contact), which may account for why some intimate partners report greater harmony with controlled intercourse. Certainly the links that are turning up between pheromones, subconscious associations, hormones and behavior suggest this is theoretically possible.

Whatever the precise mechanism of the common phenomenon of emotional distance between lovers after orgasmic sex, the good news is that, for many couples, controlled intercourse somehow counters it.

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