With a heat wave sweeping much of the United States this week, many Americans are undoubtedly wearing as little as possible, and all that bare skin may have effects beyond cooling. As the premise of the indie film 30 Beats (out July 20) or the steamy ice-cube scene from Spike Lee’s Do the Right Thing demonstrate, many people believe that sweltering temperatures have a tendency to push us into one another’s arms. Do high temperatures really contribute to an increase in sexual activity?
It depends. The most concrete measure of rates of sexual activity is the seasonal pattern of birth rates. As it turns out, the numbers depend on where in the world you live. According to one literature review (PDF), in southern and tropical climates, births tend to decrease in the spring, indicating that conception was less common during the previous summer. Researchers postulate that deterioration of sperm quality during the hot summer months may depress fertilization success. Other research shows a decrease in testosterone levels—and therefore possibly sexual desire—in men during the same period. People living in cooler northern climes demonstrate the opposite pattern, with peak birth rates occurring in the spring—nine months after summertime.
According to condom-manufacturer Trojan’s “Degrees of Pleasure” survey, respondents living in the hottest areas, such as Miami, reported having more sex on average than their peers in areas like Minneapolis and Seattle. Still, even Miamians might turn down a proposition on the hottest days—according to the same study, 35 percent of Americans have said no to sex because of the heat.
Assuming pleasant-to-bearable heat, what might explain an increased interest in hooking up? Sweat may play a role, but not because of pheromones, those mysterious airborne compounds that allow animals to communicate all manner of messages from fertility to fear. Though the science on pheromones in humans is still sketchy, we probably do excrete some chemicals related to attraction. However, as studies on a number of animal examples (PDF) show, increased heat has a tendency to degrade these compounds. Pheromones are not the only possible scent-based seduction aids—a mix of factors such as skin bacteria and diet contribute to each person’s distinctive smell, and increased sweating assists in the scent’s promulgation.
But perhaps the answer isn’t as complicated as chemistry. With summer’s longer days, people spend more time outside, giving them more opportunities to interact with one another. Moreover, when they do meet, they’re more likely to be showing some skin; though men and women may experience visual attraction a bit differently, most people find bare flesh somewhat alluring. However, this effect may not explain the seasonality of sex. According to a 2007 study of 114 Polish men, the subjects found images of women’s bodies and breasts (but not faces) more attractive when tested during winter than summer. The researchers theorize that the result may be due to men’s habituation to the glut of nude skin on display during the warmer months.
One last possibility: According to research on “embodied cognition,” humans are primed to conflate temperature with emotional perception of relationships. Specifically, a paper by Matthew Vess of Ohio University suggests that, in many people’s minds, the concept of warmth is associated with intimacy. Moderate heat may well make people more friendly and open to connecting socially, which, unsurprisingly, may lead to all kinds of other connections.
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