In post-menopausal women if they are not taking estrogen replacement or in younger women who may have had a hysterectomy and removal of ovaries, the lining of the vagina thins (Atrophic vaginitis), and can cause a dryness and discomfort following penetration. Vaginal lubricants usually can overcome this type of "dryness". (Astroglide or Slippery Stuff)
Low estrogen can also cause this issue in younger women while they are nursing their baby, as the menstrual cycle often ceases during the months of breast feeding. There are other less common reasons for estrogen decrease in younger women as well.
The largest misconception, however, that we see so commonly, is that whatever the age of a women who is trying to be sexually active, especially pre-menopausally, the most common reason for entrance pain being so severe as to avoid intercourse, tampons, vaginal speculum or even light touch to the opening is NOT dryness of the vagina but variable levels of sensitivity of the "vestibule", which is the tissue between the outer skin and vaginal lining, (the inside of the labial lips). This condition is called vestibulitis or vestibulodynia, which we explain in more detail in our upcoming DVD.
Unfortunately, too many women of all ages with this condition are mistakenly treated with estrogen replacement therapy, either by mouth or by vaginal cream or pill, which can be very helpful for simple vaginal dryness, but usually does not help vestibular sensitivity or severe pain, and sometimes makes it worse.
Vestibulodynia is a common subset of another condition known as Vulvodynia which is estimated to affect up to 15 million women in the USA alone.