June has arrived, with warmer weather and people showing more skin, which by itself often gets our erotic feelings flowing. But warm sun and visible flesh may not be the only reasons you’re feeling friskier this month: There's a surprising body of little-publicized research showing that interest in dating, mating, and sex actually follows annual cycles, with valleys in the spring and fall, and peaks in summer and winter—particularly the months of June and December:

  • Studies of birth records consistently show that more children are conceived during summer and winter than during spring and fall.
  • Condom sales rise and fall seasonally, with the largest proportion of sales in summer and winter.
  • Surveys of virginity loss consistently show two seasonal peaks for first intercourse—one in May/June, the other in December.
  • Sexually transmitted infections also show cyclic variation, with the greatest number of diagnoses occurring in summer and around Christmas.

Feeling Lucky?

Adding to the scientific literature, a recent study explored sexual seasonality in a new and innovative way—by comparing Google searches of sex-related and sexually-neutral keywords. Patrick Markey, an associate professor of psychology at Villanova, and Charlotte Markey, an associate professor of psychology at Rutgers, analyzed millions of Google searches from 2006 to 2011. For the study's purposes, sexual keywords were those focused on dating, including sites like eHarmony, Yahoo Personals, Match.com, OkCupid, and JDate; a range of pornography domains; and sites related to sex work including those for escort services and brothels. Non-sexual keywords included those in searches about pets, auto parts, and generally popular websites such as Facebook, YouTube, and Yahoo.


Searches for the non-sexual keywords tracked in the study remained constant year-round, but searches of terms leading to dating, pornography, and sex-work showed clear seasonal cycles, with statistically significant peaks during the summer and winter months, and declines during the spring and fall.

One limitation of this study is that men initiate the vast majority of searches for pornography and sex work, which might have introduced a gender bias and skewed the findings. However, both men and women search dating sites, and those searches showed the same clear pattern—peaks in summer and winter, and valleys in spring and fall.

Something in the Air?

It’s not clear why sexual interest and activity peak during summer and winter. Some researchers speculate that it may simply have to do with our calendar. Christmas, New Year's Eve, Valentine’s Day, and summer vacation are all times when people take breaks from school and work and are more likely to meet, socialize—and more. Other researchers suggest that subtle seasonal changes in our hormone levels may have something to do with the human sex cycle.

Another theory is that this sexual seasonality reflects our mammalian heritage. A key difference between humans and other mammals is that women have menstrual cycles, while dogs, cats, and other mammals have estrous cycles (“estrous” from the Greek for sexual desire). Those non-human mammals are sexually inactive most of the year. Then, at predictable intervals—twice a year for animals like deer, elk, ferrets, goats, hamsters, horses, and sheep—females release fragrances that attract males, who come running and often fight one another for sexual access. In contrast, women can be sexually active throughout their menstrual cycles. Still, perhaps this apparent human sexual seasonality in summer and winter represents a distant echo of estrous.

No one knows for sure. But the research certainly makes a strong case that people are most interested in dating, mating, and sex during summer and winter. So enjoy your summer—and six months from now, have a very merry Christmas.


  • Lam, D and JA Miron. “Seasonality of Births in Human Populations,” Social Biology (1991) 38:51.
  • Levin, M et al. “Seasonality of Sexual Debut,” Journal of Marriage and Family (2002) 64:871.
  • Markey, PM and CN Markey. “Seasonal Variation in Internet Keyword Searches: A Proxy Assessment of Sex Mating Behaviors,” Archives of Sexual Behavior (2013) 42:515.
  • Parnell, AM and JL Rodgers. “Seasonality of Induced Abortions in North Carolina,” Journal of Biosocial Science (1998) 30:321.
  • Pittman, S et al. “Seasonality and Immediate Antecedents of Sexual Intercourse in Adolescents,” Journal of Reproductive Medicine (2005) 50:193.
  • Schroeder B. et al. “Is There Seasonal Variation in Gonorrhea and Chlamydia in Adolescents?” Journal of Pediatric and Adolescent Gynecology (2001) 14:25.
  • Seiver, DA. “Trend and Variation in the Seasonality of U.S. Fertility, 1947-1976,” Demography (1985) 22:89.
  • Tita, ATN et al. “Seasonaity in Conception of Birth and Influence of Late Initiation of Prenatal Care,” Gynecology and Obstetrics (2001) 97:976.
  • Wellings, K et al. “Seasonal Variations in Sexual Activity and Their Implication for Sexual Health Promotion,” Journal of the Royal Society of Medicine (1999) 92:60.

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