Losing weight, out of politeness or simply to cure a headache... The REAL reasons women have sex

By Cindy Meston and David Buss
Updated: 06:20 EDT, 23 September 2009

To lose weight, out of politeness or simply to cure a headache, the real reasons women choose to have sex are much more bizarre and intriguing than you might imagine. In the first extract from a new book - Why Women Have Sex by CINDY MESTON and DAVID BUSS - we look at the fascinating science behind the most popular reasons women give for slipping between the sheets...

BETTER THAN IBUPROFEN

Everyone has heard (or perhaps used) the timeworn dodge: 'Not tonight, dear. I've got a headache.' And it's true that sex can exacerbate, or even bring on, a headache.

Head and neck muscles often tighten during sexual activity, and blood pressure can increase at orgasm, causing blood vessels in the brain to dilate, a condition technically named coital cephalgia.

However, in our study we discovered that some women choose to have sex with the goal of getting rid of a headache.

Turn on: Kissing between romantic partners occurs in 90 per cent of cultures

In the words of one 62-year-old: 'I suffer from migraine headaches and I find that when I have sex during a headache, especially if I have an orgasm, it goes away.'

One woman reported that her doctor prescribed sex as a way to relieve migraines.

But how can sex serve as a headache catalyst and cure? During sexual activity, the body releases feel-good endorphins, the brain chemicals that bear a remarkably close resemblance to morphine. Endorphins serve as powerful pain relievers.

The release of endorphins can relieve headaches, according to research at the Headache Clinic at Southern Illinois University.

In its study of 58 women migraine sufferers who had engaged in sex during an attack, almost half reported at least some headache relief through orgasm. Only three found that having an orgasm made their migraine worse.

Some headache researchers believe that there is a headache generator in a specific area of the brain, and that orgasms might somehow switch it off.

This would explain why headache relief from orgasms is permanent, as opposed to lasting only a few hours, as might be the case if endorphin release was the sole cause.

BECAUSE HE'S A GOOD KISSER

Another popular reason many women cited for having sex turned out to be astonishingly simple: the man was a good kisser.

Kissing between romantic or sexual partners occurs in more than 90 per cent of cultures. Human lips are densely packed with sensory neurons - more than in most regions of the body - but the tongue, nose and cheeks also come into play.

One study found that kissing caused a drop in cortisol, a stress hormone, indicating a reduction in anxiety.

Kissing also conveys information about health status, since bad breath can be a sign of disease or ill-health.

Women seem to use kissing as an emotional litmus test, with the outcome revealing whether they should take things to the next level in a relationship.

Kissing seems more important for women than for men for this function. While 53 per cent of men in one study said they would have sex without kissing, only 15 per cent of women said they would consider sex with someone without first kissing them.

But 'bad' kissing is a sexual turn-off. One study found that 66 per cent of women (as compared with 58 per cent of men) admitted sexual attraction evaporated after a bad kiss.

Some woman admit to having sex to stop their man from straying

TO GET REVENGE

Some women said they had used sex to exact revenge on their unfaithful partners.

'My husband cheated on me a few years ago,' one wife told us. 'I had put on weight after having our daughter, so felt incredibly worthless. Within six months of discovering his affair, I lost weight and had a fling with his best friend. It felt great.'

The fact that many instances of sex for revenge involve sleeping with a former partner's best friend highlights the delight and relish with which this vengeance is taken.

TO LOSE WEIGHT

Yes, sex can help you lose weight, and we came across women in our survey who said they increased sexual activity for this reason.

Depending on which report you read, a sexual session can burn anything from 100 to 250 calories. Clearly the range is related to the level of athleticism. Ballet manoeuvres and handsprings will burn more calories than lying back and thinking of England.

According to a survey of more than 1,400 women aged 18 to 59, women have sex 6.3 times a month. The average is slightly higher among 20 to 30-year-olds (7.5 times a month) and lower among 50 to 60-year-olds (four times a month).

Given that a pound of fat is equivalent to 3,500 calories, the average woman burns 3.78lb of fat a year having sex. So, if she stopped having sex, in ten years she would be 2st 10lb heavier.

Viewed another way, if a woman had sex four times a week instead of twice, or extended the session from the average 18.3 minutes to 36.6 minutes, she would lose an extra 4lb of fat a year.

Or she could remain the same weight and consume an extra 17 chocolate sundaes, 23 doughnuts and 14 champagne truffles a year - definitely food for thought. 

Younger ones admit they engage in nookie to improve their erotic skills

WIFELY DUTY

Many women, particularly married ones, claim they often have sex with their partner when they are really not in the mood for it because they view it as their duty.

As one 53-year-old woman put it: 'I have been married for 32 years. It seems only natural after such a long time that once in a while you have sex with your husband only because you feel that it is your duty.'

For some, believing that sex is a marital duty may be embedded in their religious beliefs, but for others the notion stems from generations of cultural expectations that the man was the breadwinner.

In return, it was the wife's responsibility to raise the children, run the household and please the man.

Pleasing the man included fulfilling his sexual needs, regardless of how different they were from your own.

Though today many wives work to support the home financially, too, these messages are still conveyed from older, more traditional generations to younger women.

SYMPATHY SEX

Women are taught to be nurturers from an early age: to show empathy and compassion and to be sensitive and aware of other people's feelings.

Women, for the most part, are the ones who take chicken soup to the sick, home-made cake to the elderly and...sex to the forlorn?

Several women in our study described using sex as a way to nurture people who were feeling bad about themselves.

More than a few women in their late teens and 20s reported having sex with men because they felt sorry for them: some because the men were desperate to lose their virginity or were unable to get dates.

Having sex out of a sense of nurturing obligation wasn't limited to young women or casual sexual activity, either. One middle-aged woman was having sex with a male contemporary because he had just gone through a divorce and she felt bad for him.

And within established relationships, several women in our study talked about having sex - even when they didn't really feel like it - because they wanted to make their partner feel loved and secure.

TO STOP HIM STRAYING

As a highly social species, we are threatened by potential mate poachers, who try to lure away our partners for brief sexual encounters or a more permanent relationship.

We also constantly face the risk that our partners may be tempted to leave the relationship in the hope of trading up to a more desirable partner.

Among dating and married couples, our research has revealed that women often use sex to protect their relationships.

They give in to their partners' sexual requests in an attempt to keep them happy, they act sexy to take their partners' mind off potential competitors and they perform sexual favours or succumb to sexual pressure to entice their partners into staying.

'My husband always seems happier with me after we have sex when I initiate it,' says one 30-year-old woman. 'He spends more time with me, and doesn't seem to gawk at other women as much.'

Having sex works as a mate-guarding strategy among women for two reasons. It may keep a romantic partner faithful because they're sexually satisfied.

And being demonstrative in public - and thereby hinting at a healthy sexual relationship - can serve to ward off potential would-be mate poachers.

FOR PRACTISE

Many women in our study, particularly younger ones, cited improving their erotic skills as a motive for gaining sexual experience. Some said they wanted to gain sexual experience to avoid the humiliation of being viewed as sexually inexperienced:

'The first time I had sex, a big part of the reason was that I was 19 and felt it was time I learned how to have sex...and it was mostly just because I wanted to know what I was doing the next time,' said one young woman.

'It wasn't that I wanted to lose my virgin status; being a virgin didn't bother me. It was just that I felt someone of that age was expected to know what they were doing sexually, so I did what I thought I needed to in order to learn what I was doing.'

Sexual science has documented that the more sexually experienced a woman is, the more likely she is to have an orgasm.

The reason is simple: the more a woman has sex, the more opportunities she has to learn what feels good to her sexually and how to have an orgasm.

Sexual experience can also explain why it is often said that women peak sexually in their 30s - a saying backed by research as early as the classic survey conducted by Alfred Kinsey in the early Fifties. Along with confidence comes the ability to communicate sexual needs and desires to a partner.

But in long-term, committed relationships, being sexually experienced may not always be a good thing.

For example, what if a woman finds a partner who is perfect in many ways - they share the same interests and life goals, and are attracted to each other, and he is intelligent, kind and loyal - but her near-perfect mate is seriously lacking in the lovemaking department and doesn't seem to have what it takes to learn?

Some would argue that being sexually experienced before marriage is not a good thing - that not knowing what else is out there is better in the long run.

If a woman chooses the informed shopper option, she then runs the risk of having to deal with the fact that her chosen mate may not live up to her sexual memories.

But if she can put such past experiences into their proper context, and to recognise that wildly passionate lovers do not always make the best long-term mates, then there is no reason why such memories should negatively impact her sex life.

• Extracted from Why Women Have Sex by Cindy M. Meston and David M. Buss, to be published by The Bodley Head on October 1 at £12.99. To order a copy (P&P free), call 0845 155 0720.