In most women, the wall of the vagina responds to arousal by producing a liquid that moistens the vagina and its entrance, making penetration easier. Sometimes there isn’t enough lubrication — you may need more time for stimulation, or you may be nervous or tense.
Insufficient lubrication can also be caused by lowered levels of estrogen, which can make vaginal tissue more fragile and affect the vaginal walls in such a way that less liquid is produced. Some women experience insufficient lubrication during perimenopause and after and may need to look for signs other than vaginal wetness to signal arousal. Others, regardless of their age, simply produce less lubricant.