Dark bags under eyes can be hereditary. Hollow space under the eyes is usually linked with the aging process. As we age, fat comes out of the space enclosed by the eye socket, that leads to dropping in volume. Another process that is simultaneously happening is losing bone mass, that causes eye sockets to become bigger thus causing overall older appearance.
Dark bags under the eyes can be treated with mesotherapy by using special cocktails applied to the region.
Hollow eye can easily be improved by using hyaluronic fillers.