A little-known but widespread condition called vestibulodynia makes any sort of vaginal penetration so painful, women who have it find having sex difficult, or in some cases, impossible. You've probably never heard of it, but anywhere from 4 to 28 percent of women 20 to 40 suffer from it. If you've ever had painful sex, read on.

Vestibulodynia is one of two types of vulvodynia, which is severe, unidentifiable pain surrounding the vagina. Vestibulodynia is distinguished by pain that's limited to the area surrounding the opening of the vagina, or the vestibule (break for laughter — the vestibule of my vagina? Like, should I be asking guys to fuck my foyer? Weird).

If you have the condition, pain can be caused by penetration during sex, putting in a tampon, or even jeans that are too tight and put pressure on that area. One the other hand, people with generalized vulvodynia experience almost constant pain, pain that can be brought on spontaneously, and the painful area is less localized. 

Previously known as vulvar vestibulitis, the condition is classified by intense burning sensations at the entry to the vagina. The diagnosis under the new name of vestibulodynia was changed in the late 1980s, but is just being more widely studied now. Though researchers still haven't identified a singular cause, but some theorized causes include injury to the vulval nerves, localized hypersensitivity to yeast infections, and pelvic floor muscle weakness. 

To remedy the severe knowledge gap about the condition, a team of researchers in Oslo are conducting one of very few qualitative vestibulodynia studies by interviewing and working with eight women who have the condition. (Yes, eight. It's a very small study.) Even among the eight women in the study group, symptoms vary significantly, according to Medical Express. Some of the women find that certain sexual positions make sex possible, and sometimes even enjoyable. But others can't have sex at all.

"I've always had pain during sex, ever since the first time," said a 23 year-old woman from the study. "It destroys your sex life in a way. He thinks, ʻall I've done is to inflict pain on her.' So it's not something you want to tell your boyfriend."

This sort of concern about sexual partners was one thing the researchers — Karen Synne Groven and Gro Killi Haugstad, both from Oslo and Akershus University College of Applied Sciences — found that the women all had in common. "Being a sex partner, that's what they talked about," Groven said. "They talked about this on their own initiative, and they had a lot on their hearts. They probably don't have many others to talk to about these issues."

One woman from the group said she's broken up with a boyfriend, because the pressure to have sex she can't physically enjoy was too intense. Another has been with her husband for 12 years, but they haven't ever had sex. There are a few viable treatment options available (like practiced muscle relaxation and surgery), but again, since so little is known about vestibuolodynia, none of the options are guaranteed to work for all women. 

This condition, and the mystery surrounding it, is similar to a much rarer female sexual condition called vaginismus, which is "an involuntary tightness of the vagina and its muscles while trying to engage in intercourse (or internal examination)." But vaginismus is often a reaction to sexual assault or rape, and the researchers told Medical Express that none of the women in their study group have a history of any such sexual trauma. 

"We don't know for sure if there are more people with experiences of sexual abuse among those suffering from vestibulodynia than among people suffering from other long-term pains," Haugstad said. "This is also something which may be very difficult to talk about and bring to light."

Previous research has theorized that women affected with vestibulodynia tend to live more stressful lives, but the researchers of this latest study don't find that to be necessarily true.

"They weren't more stressed than other girls in their twenties," Haugstad told Medical Express. "At the same time, these women feel insufficient, which is also a type of stress. They don't feel like true women, they can't have sex. They think about this a lot, some more or less all the time. It's a mental stress that may contribute to the persistence of these pains."

Haugstad and Groven are working to publish their research in an effort to spread information about vestibulodynia, and help women experience sex that isn't painful, but actually enjoyable.