Sex is painful for nearly one in eight women, according to a study in the British Journal Of Obstetrics And Gynaecology.
Researchers vary in their estimates of how common painful sex is - some studies say it affects up to one in three women - but all of them agree that it is a neglected problem.
Most women do not seek help. Some carry on having penetrative sex through gritted teeth.
The medical name for painful sex - dyspareunia - covers a multitude of reasons that intercourse hurts, such as sexually transmitted diseases (chlamydia or herpes), thrush and endometriosis (which causes pelvic inflammation). There is also anxiety, lack of sexual arousal and/or a previous traumatic experience of sex.
This latest study used survey data from the third annual National Survey of Sexual Attitudes and Lifestyles, based on 6,669 sexually active women, and found those in the ages of 16 to 24 and 55 to 64 were most likely to have pain during sex.
Women were also asked about other aspects of their sex lives. Those who said sex hurt were:
• Three times more likely to have difficulty climaxing.
• Four times more likely than other women not to enjoy sex.
• Five times more likely to feel anxious during sex.
The strongest link found was between painful sex and vaginal dryness. "In the older age group, this is likely due to hormonal changes during menopause," said Dr Kirstin Mitchell, a senior research fellow at Glasgow University's Social and Public Health Sciences Unit and lead author of the new study.
"But, in the case of the 16- to 24-year-olds, it may be about young women not feeling sufficiently aroused and, therefore, not lubricated enough, so that penetration is painful. Young women may then grow up thinking that sex hurts."
But, certainly, there are enough medical causes for painful sex to merit getting checked out by your doctor or sexual-health clinic.
"You need to understand what's causing the pain," said Dr Mitchell.
Menopausal women often find that lubricants help relieve vaginal dryness.
Relationship problems and previous traumatic experiences of sex need more help, while infections and inflammatory conditions need medical treatment.