Ectropion describes the sagging and outward turning of the lower eyelid and eyelashes. The edge of the eyelid and the eyelashes turn out and this rubbing can lead to excessive tearing, crusting of the eyelid, mucous discharge, and irritation. During blinking, the eyelids normally sweep across the surface of the cornea and with this condition, tearing occurs because the eyelids are not able to wipe the surface of the cornea properly to pump the tears into the tear duct.

Most cases of ectropion are due to relaxation of the tissues of the eyelid as a result of aging. Some cases result from scarring of the eyelid caused by chemical and thermal burns, trauma, skin cancers, or previous eyelid surgery. Rarely, ectropion can be present at birth if the eyelids do not form properly.