Loose skin on the upper and bottom eyelid is caused by the skin on the eyelids losing its elastic fibres and grows weak. Heavy eyelids may also be caused by changes in the connective tissue of the eyelids and there might be fatty tissue bagging out from behind the eyelid.
Loose and weak skin on the upper and bottom eyelid is age-related and especially seen with smokers, people who tan a lot and can be hereditary.
If the excessive skin causes problems with opening the eyes or reduces the field of vision, it can be removed with a small surgery under local anaesthesia. Some people choose to have the excessive skin removed because it is a cosmetic issue.