Nearly one in 10 British women finds sex painful, according to a big study.
The survey of nearly 7,000 sexually active women aged 16 to 74, in BJOG: An International Journal of Obstetrics and Gynaecology, suggests this medical problem - called dyspareunia - is common and affects women of all ages.
Women in their late 50s and early 60s are most likely to be affected, followed by women aged 16-24.
Doctors say there are treatments that can help if women seek advice.
But many still find the subject embarrassing and taboo, the survey results show.
Painful sex was strongly linked to other sexual problems, including vaginal dryness, feeling anxious during sex, and lack of enjoyment of sex.
However, there can be lots of different physical, psychological and emotional factors causing painful sex, which can be complex to treat.
Some women said they avoided intercourse because they were so afraid of the pain.
'It hurt so much'
Karen (not her real name) is 62 and from Greater London. She said her problems began around the age of 40.
"I felt that my sex drive dipped quite considerably, arousal seemed to take longer, and, despite an understanding husband, I started to dread him making approaches.
"It's like any muscle group I guess, the less you use it the worse it gets."
Karen tried using lubricant but still encountered problems.
"It became like a vicious cycle. You worry and get tense and that only makes it worse."
Karen developed another complication called vaginismus - involuntary tightening of the muscles around the vagina whenever penetration is attempted.
"It wasn't just in bed. It happened when I needed smear tests too. I would be crawling up the bed away from the nurse because it hurt so much."
Karen spoke to her doctor who recommended she try oestrogen creams and pessaries for the dryness and dilators to help with the involuntary tightening.
"Women need to know that there is help out there for these kinds of problems, especially as we are all living longer.
"You shouldn't have to be writing off your sex life in your 50s.
"Many women don't like to talk about it. We share all the gore of childbirth, yet women of my generation don't tend to talk openly about sex and the menopause. We should."
The national survey of sexual attitudes and lifestyles was carried out by the London School of Hygiene and Tropical Medicine (LSHTM), University College London and NatCen Social Research.
Of those who reported painful sex (7.5%), a quarter had experienced symptoms frequently or every time they had had intercourse in the last six months or more.
Around a third of these women said they were dissatisfied with their sex life, compared with one tenth of the women who didn't report painful sex.
Lead researcher, Dr Kirstin Mitchell, from LSHTM and the University of Glasgow, the said there could be a whole range of reasons for dyspareunia.
Lack of enjoyment
"In younger women, it might be that they are starting out in their sexual lives and they are going along with things that their partner wants but they are not particularly aroused by.
"Or they might be feeling tense because they are new to sex and they are not feeling 100% comfortable with their partner."
Painful sex might be caused by other health problems, such as sexually transmitted infections, endometriosis and fibroids, which should be diagnosed and treated.
Women around the age of the menopause can find sex painful because of vaginal dryness.
Dr Mitchell says it's not just older women who can feel embarrassed talking about painful sex, even though the condition is common.
Other research, involving about 200 university students in Canada, suggests up to half of young women find their first experience of intercourse painful.
Dr Mitchell says sex education should do more to better prepare young people.
"Often sex education is about STIs and pregnancy, but it should also prepare people to think about what makes sex enjoyable and how to communicate what they like and dislike in a trusting and respectful relationship."
If you have pain during or after sex, you should get advice from your GP or a sexual health clinic.
If there is an emotional reason or anxiety that is causing problems, a counsellor or sex therapist may be able to help - and your GP or sexual health clinic can refer you to one.