A tampon can fall out if it is not inserted far enough into the vagina or if it is nearing its absorbency capacity. A properly inserted tampon that is changed regularly does not usually fall out because there are muscles at the vaginal opening that keep it in place.
A tampon that is not inserted far enough can be quite uncomfortable, even if it does not actually fall out. If a woman has trouble getting a tampon that requires insertion with a finger far back enough into the vagina, she can try using a tampon that comes with an applicator. If she already uses tampons with applicators, she might try a different type of applicator or a lower-absorbency tampon. A lower-absorbency option is smaller and may be easier to insert as far back as needed.
The more saturated a tampon gets with menstrual blood, the heavier and more slippery it becomes. To avoid a tampon slipping downward, a woman should insert a new tampon every four to eight hours, depending on her flow. A full tampon is especially more likely to fall out while a woman is having a bowel movement or engaging in another activity that involves pushing down with the abdominal muscles.