Some people would argue that the most important part of sex is what comes immediately afterward: the afterglow. Whether or not they’re accompanied by a post-coital cigarette, the radiant moments following sex involve a warm outpouring of good vibes and well-being for all parties involved. To most people, the afterglow is just a happy bonus that comes with sex, but as scientists recently showed, all those good feelings serve a very important purpose, too.

In a study recently published in the journal Psychological Science, researchers attempted to figure out what that purpose might be. They hypothesized that the afterglow must serve some evolutionary benefit in addition to simply feeling pleasurable. While scientists had previously suggested that it must have something to do with cementing the bonds between sexual partners, the researchers thought it was weird that most adults only have sex with their partners every few days.

Could it be, they wondered, that the afterglow is what helps couples stay together through the days they’re not having sex?

On average, the afterglow effect can last for 48 hours.
On average, the afterglow effect can last for 48 hours.

To find out, they analyzed data from two independent surveys on newlywed couples, one with 96 couples and another with 118 couples. In both of the studies, each member of the couple was asked to keep a 14-day “sex diary,” tracking the days they had sex and evaluating their satisfaction with their sex life, their partner, and their relationship as a whole.

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The data revealed something surprising about the afterglow: On average, it lasts a full 48 hours after sex happens. That two days’ worth of post-coital good vibes, the data suggest, helps to boost the overall satisfaction of the people in the relationship. Despite the fact that participants only had sex an average of four times over the course of the 14-day study, the data showed that “having sex on a given day was linked with sexual satisfaction that same day, which was linked with sexual satisfaction the next day and even two days later,” as a statement on the study explained.

“[People] with a stronger sexual afterglow — that is, people who report a higher level of sexual satisfaction 48 hours after sex — report higher levels of relationship satisfaction several months later,” lead author Andrea Meltzer, a psychological scientist at Florida State University, said in a statement.

It makes sense that evolution would have configured human sex lives this way. While the study suggests it would be even better for people in relationships if they simply had sex all the time, the authors acknowledge that’s just not possible. “Yet, despite the apparent benefits of sex for long-term relationship stability, there are significant costs to having constant or uninterrupted sex,” they write, noting that sex requires time and energy, and when people are having it they let their guard down against external threats. The afterglow, it seems, helps mitigate the amount of sex we need with the amount of sex we can feasibly have.

The findings are in line with recent research suggesting that the happy feelings we associate with sex are derived from post-coital cuddling, not the sex itself. They stand as a reminder that, while sex itself can always feel good, sticking around afterward could be the trick to feeling great.

Photos via Flickr / leodirac