Vaginismus is a condition which affects a woman's ability to have sexual intercourse, insert tampons and undergo gynecological examinations. This is the result of a conditioned muscle reflex of the pubococcygeus muscle in which they clamp shut, making penetration either extremely painful or impossible. The severity of vaginismus varies from woman to woman.

It is important to remember that the woman does not choose for this to happen; it is a reflex reaction. Vaginismus can be compared to the response of the eye shutting when an object comes towards it. A woman with vaginismus learns to expect pain to come with penetration and so her mind automatically sends a signal to her PC muscles to clamp shut, thus making penetration either impossible or very painful.

The condtioned reflex creates a vicious circle for vaginismic women. For example, if a teenage girl is told that the first time she has sex it will be very painful, she may develop vaginismus because she expects pain. If she then attempts to have sexual intercourse, her muscles will spasm and clamp shut which will make sex painful. This then confirms her fear of pain as does each further attempt at intercourse. Every time the fear is confirmed, the brain is being "shown" that sex does hurt and that the reflex reaction of the PC muscles is needed. This is why it is important that if a woman suspects she has vaginismus, she stops attempting to have sexual intercourse. This does not mean women with vaginismus can not partake in other sexual activities, as long as penetration is avoided. It is a common misconception that these women do not want to have sex as a lot of the time, they desperately do.