The eyelash is a kind of hair in people' body, so that it has its own lifecycle. However, the eyelash has one of the shortest hair lifecycle, which is between 3 to 5 months. After the period, it would be fall out with 1 to 3 hairs every time. It is the normal process of metabolism. Another situation is maybe you get blepharitis, which causes by bacterial infection of eyelash and the edge of the eye. You had better go to see eye doctor to check whether you get blepharitis, if your eyelashes are falling out too much once.