I was talking with my friend Erin* and she told me she gets anxious when she doesn't get to have sex with her boyfriend after a few days. "I feel amazing during and after sex with my partner," she said. "Then—if three or four days go by without sleeping together—I start to worry. Since we work opposite schedules, we get tired at different times, which can lead to falling asleep without hooking up. That's fine, but I begin to have a nagging feeling that it's bothering him, though I've been assured it's not." She added, "Once we've successfully fucked again, that slate is wiped clean."

Recent research may explain why: Past studies have suggested that sex plays a key role in pair bonding and relationship satisfaction. But, according to Florida State University researcher Andrea Meltzer, they don't illuminate how partners "remain pair-bonded between sexual acts." In a new study, published in the Association for Psychological Science, she introduces the phenomenon of a "sexual afterglow" to explain this. Meltzer found that the positive effects of sex on relationships can linger after the act—but only up to 48 hours.

Read more: What Swearing Off Sex Does to Your Brain

The researchers examined data from two longitudinal surveys— one with 96 married couples and one with 118 married couples—which asked the newlyweds to keep individual, daily sex diaries to report when they had sex, their perceived sexual satisfaction levels, and their relationship satisfaction levels. Meltzer noticed that couples reported heightened sexual satisfaction up to two days after having sex. "Participants who reported a stronger 48 hour sexual afterglow [also] reported higher levels of relationship satisfaction four to six months later," she said in an interview with Broadly.

"This research is important because it joins other research suggesting that sex functions to keep couples pair bonded," Meltzer noted. From an evolutionary perspective, Meltzer says that the downsides of sex could account for the afterglow phenomenon. Frequent copulation, she points out, takes time and energy, and may decrease sperm count.