Like the hair on your head, eyelashes go through a growth cycle. During this cycle, they grow and shed about every six to ten weeks. If your lashes are falling out frequently, it may be time to check in with a doctor about the cause. Sometimes lash loss can be the first sign of an underlying health issue, such as an imbalance in hormones or thyroid disease.
Source: https://writeonwall.com/how-many-eyelashes-do-you-lose-a-day/