Sex studies: Blushworthy headlines of 2013

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The worst stereotypes of science suggest that it's boring, staid, or overly complex.

Not these studies. More often than people may think, science gets downright dirty, peering into bedrooms and asking nosy questions about secret fantasies. The science of sex is anything but dull.

With that in mind, here are 10 of the sex stories most likely to have caused blushing in 2013.

1. More housework, less sex?
Egalitarianism in household chores may not lead to scorching hot action in the sack, according to research published in February in the journal American Sociological Review. The study researchers found that men who did "feminine" chores such as cooking and washing had less sex than those who did not.

The research was correlational, so chores may not be a direct turnoff, but egalitarian relationships may be less spicy, the researchers said. However, research does show that people in equal partnerships are happier. [Busted! 6 Gender Myths in the Bedroom & Beyond]

2. After baby, women wait
Doctors usually clear new moms to have sex six weeks after delivery, but most wait a bit longer at least for vaginal sex. Whereas 41 percent of women had resumed vaginal sex within six weeks, 65 percent had by eight weeks. By 12 weeks, 78 percent had resumed sex. By six months, that number was 94 percent.

But more than half (53 percent) of women had engaged in some sort of sexual activity by six weeks, the researchers reported in February 2013 in the BJOG: An International Journal of Obstetrics and Gynaecology.

3. So do dads
After childbirth, moms aren't the only ones who experiences sexual changes. Dads have highs and lows, too. Fatigue, stress and babies who won't sleep were the main factors keeping new dads from feeling sexual desire. Factors such as their partner's breastfeeding or vaginal bleeding were less of an influence, researchers reported in August 2013 in the Journal of Sexual Medicine.

4. Sex for headache relief
"Honey, I have a headache" may be more of a come-on than an excuse, at least if a study published in March in the journal Cephalalgia is to be believed. According to the study, about a third of migraine sufferers get relief from getting busy.

It's not clear why sex would relieve some migraines, but endorphins released by the brain during sex may explain the soothing effect, the researchers said.

5. Bats have oral sex
Humans aren't the only species to get sexually creative. A bat species called Indian flying foxes (Pteropus giganteus) does, too. Male flying foxes perform oral sex on females before penetration, researchers reported in March 2013 in the journal PLOS ONE. The oral sex seems to prolong the sexual encounter, the researchers said, perhaps increasing the chances of conception. The male bats may also be removing competitors' sperm from the females' vaginas, they added.

6. Hookup culture isn't so wild
Popular media often portrays modern college students as hopping from bed to bed in a series of casual sexual relationships. But "hookup culture" is overblown, according to research presented in August 2013 at the annual meeting of the American Sociological Association.

Researchers compared responses from national representative surveys of 18- to 25-year-olds taken in 2002-2010 and in 1988-1996. They found that in both groups, about 31 percent said they'd had one sexual partner in the last year. Only half reported having more than two sexual partners after age 18. In other words, college kids don't appear to be getting more promiscuous.

7. Sex as exercise?
Those college kids could be missing out on some moderate caloric burning, according to research published in October 2013 in the journal PLOS ONE. The study used wearable fitness monitors to track couples as they had sex in the course of their everyday lives. It found that sex burns an average of 4.2 calories a minute for men and 3.1 calories a minute for women. [Sexy Tech: 6 Apps That May Stimulate Your Sex Life]

That's better than a walk, but not as good as a jog. While sex may not be the most efficient exercise for weight loss, the authors noted that at moderate intensity, it could count as part of someone's daily workout.

8. Hookups don't lead to orgasm for women
Casual "hookup" sex is anticlimactic for women much of the time, according to a November study of 600 college students. Hookup sex was half as likely to lead to an orgasm as sex within a relationship for women, the researchers found. Relationships may be more orgasm-friendly for women, because her partner learns what she likes and cares about her needs, the researchers suggest.

In other climax news, orgasms may start in the foot. A 55-year-old woman whose experience was reported this year in the Journal of Sexual Medicine said the sensation started in her left foot, traveled up her leg to her vagina, causing what felt just like an orgasm achieved during sex.

9. How hormones influence sex
The hormonal influences on the female sex drive are tough to uncover, partially because many women in relationships may have sex when they're not necessarily "in the mood." But for a study published in October 2013 in the Journal of Sexual Medicine, researchers took a hard look at how the hormones associated with ovulation influence sex drive. It turns out that single women have more sex around ovulation, suggesting this window of fertility may nudge women toward sex. However, women in relationships were less influenced by biology, the study found.

10. Male birth control blocks sperm
The search for effective and safe male birth control beyond condoms continued in 2013, with a promising rodent study suggesting there may be hope for manly contraception. The method uses a combination of drugs that allow sperm to be produced as usual, but prevent that sperm from traveling through the vas deferens and out of the urethra during ejaculation.

The road from rodent studies to human drug trials is long, but researchers are hopeful, they wrote in December in the journal Proceedings of the National Academy of Sciences though there is one catch.

"A lack of ejaculate has the potential to be disconcerting," the researchers wrote in their study.

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