When any group of married women get together for a no-holds-barred chat and the conversation turns to sex, it's likely that one — maybe even all — of them will admit to having gone off sex at some point.
They might joke about their loss of libido, but the reality is that it can become a corrosive problem that causes crippling guilt in the woman who suffers it and forces untenable compromises on her relationship.
Family planning and Relate relationship clinics report large numbers of women complaining of low libido, with some estimating hundreds of thousands of women suffer from it in the UK.
It can strike at any age and the cause can be emotional, psychological or medical.
Stacy Hill, an office manager who lives in Exeter with her partner Tom, 29, is one of the many who have suffered from the condition. Now 33, she lost her sexual desire at the relatively young age of 30 when she started the menopause. 'My libido disappeared over a period of months and is linked to my crushing fatigue. It is awful,' Stacy says.
'I get into bed and just conk out. My loss of desire is nothing to do with my love for Tom — it is very much a physical issue. I don't worry about Tom straying because of the lack of sex — he isn't that type — but the situation has made me wonder if he will stay with me.'
Tom, who runs his own IT business, has been supportive, but that doesn't stop Stacy feeling guilty. 'It must be awful for him,' she says. 'Our relationship has had to change emotionally, and he must feel rejected.'
Hand-in-hand with the tiredness came other changes, including hair-thinning and dry skin, neither of which helped Stacy feel any better about herself at a very vulnerable time.
'The menopause has made me highly emotional, and I seem to cry at anything. What worries me most is that my periods have stopped, so I'm not sure I'll be able to conceive,' she says.
Stacy is hopeful that with hormone replacement her periods may begin again, but if not the couple will explore other fertility options. She says: 'I'm so tired that when I come home from work, I can fall asleep on the sofa by 9pm, whereas I used to be ready to make love when we went to bed.
'I am speaking out because there are many other women in this situation, but you feel so alone when it happens to you.'
Stacy is right about there being many other women in her predicament.
A recent study by the British Women's Health Information Service revealed 43 per cent of women experience loss of sexual desire at some point in their lives. The emotional triggers include stress, anxiety, family concerns, financial worries and marital break-up.
The primary psychological trigger is depression, with anti-depressants such as Prozac sometimes having a negative impact on libido. The medical conditions are the menopause, cancer, hypertension, heart disease, diabetes, thyroid disorder and neurological disorders such as MS.
Women also often lose their sex drive because of low hormone production, most commonly experienced around the time of menopause.
Like Stacy, Louise Sinclair, 51, a professional poker player, blames the menopause for her loss of desire three years ago, and doesn't mince her words about the impact of this.
'I felt as if I had the female equivalent of castration, which had such an impact on the rest of my life. I felt totally demoralised and depressed, and I couldn't stop crying,' she says. 'My husband tried to cuddle me, but I would turn away from him.
'I'm sure it's possible to have a marriage without sex, but it has a devastating impact on any sense of intimacy — and couples need to make love to feel valued. There are a lot of women out there suffering from loss of libido but they won't admit it, and I'm convinced that's why so many marriages fail in later life.'
Louise started suffering the symptoms of early menopause in 2008, when her sex drive disappeared and her energy slumped. 'My husband Gary and I had always had a great sex life, and I worried whether our marriage would survive without it,' says Louise, who lives with Gary in London.
'When Gary touched me I began to pull away from him. I had no sexual desire whatsoever — it was as if my pelvic nerves were deadened, and I had no sexual response.'
Louise told Gary, a 46-year-old civil servant, she thought the cause was hormonal and saw her GP, then consulted a Harley Street specialist who prescribed hormone therapy. The treatment was costly at £750, but Louise says her libido is now almost back to normal.
'I felt dismissed by the NHS — all I was offered were vitamin pills — so I went private and have had very sympathetic treatment from my menopause specialist,' she says.
The Mail's sex columnist Rowan Pelling says that it's time we stopped seeing a loss of sexual appetite as a sign of failure: 'We're sold the false expectation that we should be having fantastic sex well into our 70s, but the fact is that libido will decline as we get older. At some stage it's quite normal to think: “I'd rather read a good book.”'
Sarah Simmonds may not be in that camp quite yet, but at 53 she admits to having a 'squashed' libido. Twice-divorced and now single, Sarah says her dormant desire is bound up with her sense of herself and her desirability as a woman.
'A woman's libido fluctuates. When you're young, it's always there. When you have children, it begins to fade — and when you reach 50, unless you're with a man who makes you feel attractive, it can fade away all together,' says Sarah, who lives in Cardiff and works as a health trainer.
'I'm like many women in that my libido is bound up in my sense of identity. The stronger and more confident you feel, the stronger your libido. After two divorces, I feel very vulnerable.'
Sarah, who has three grown-up children and one grandchild, says her libido collapsed in 2005, around the time of her second divorce.
Divorce, she says, feels like rejection: 'Throw in the menopause, putting on weight and knowing you are no longer fertile, and it's no wonder so many women lose their libido in their 50s. I sometimes wonder if anyone will ever want me again.
'I don't think a woman's libido ever dies, it just depends on the man in her life. For me, it will take a very special man.'
Loss of libido isn't limited to those who have given birth or are going through the menopause, however.
Denise Knowles, a sex therapist with the relationship charity Relate, says she sees women of all ages complaining of waning desire. 'So many women say to me: “I just can't be bothered with sex.” I'm seeing increasing numbers, which I think is because of growing levels of stress.'
Denise says marrying later in life may be a factor, too, as by the time many women walk down the aisle, they are sexually experienced and have high expectations of their physical relationships.
She says: 'They've been more experimental than generations of women have ever been before, and the fact is that to some women, marital sex becomes boring.'
The good news is that a high proportion of women do eventually see their libido return. There is no quick fix, however, and, as of yet, no wonder-drug to cure it.
HRT can improve libido, while some doctors prescribe oestrogen and testosterone replacement. Most GPs say the best treatment is general good health — improving diet and taking more exercise, for example. It is rare for women to lose their libido completely, or permanently.
Some women will conquer the problem themselves, and some benefit from expert medical or psychosexual advice. Others have no real desire to experience the intense sexual appetites of their youth.
Kerry Chadwick is 41 and was diagnosed with breast cancer in her mid-30s. As a result of the illness and treatment, her libido waned around the age of 35.
'All my energy was taken up with fighting the illness and looking after my children,' says Kerry, who runs her own hairdressing salon. 'When you're diagnosed with cancer, everything is focused on getting healthy.' Kerry worried about the effect her lack of desire would have on her husband James, 46, who owns a construction company.
'It was all such a lot for James to take on. He's been brilliant, though, and thankfully, now that I'm well, our marriage is on track in every sense,' she says. In 2004, Kerry was seven months pregnant with her first child when she found a lump in her breast. It was removed after Kerry gave birth to her daughter Mia, now seven.
But the cancer came back four more times. Kerry was diagnosed again after the birth of her son, Cass in 2009, and underwent six weeks of radiotherapy and a mastectomy.
'I've tried to remain positive, but the cancer took its toll on my sense of well-being and my libido,' says Kerry, who lives in Cheam, Surrey.
'Libido is affected by your general health, your self-confidence, your body image. I felt as if I was being regularly hit by a tidal wave, and it was all I could do to survive.
'We had to draw on other resources in our marriage, such as a shared sense of humour. I'm taking strides forward now — my latest tests have come back clear and I'm planning to do a 26-mile walk through London to raise money for cancer research. My marriage is so important to me, and in many ways we are closer now than we have ever been.'