Brows sag as well as other facial and body structures, due to reduction in skin support or laxity as well as gravity.

Your brow is made up with skin, muscle and fascia holding it to the skull.

In addition, eyelid position is somewhat determied by the  brow.

Brow surgery, browplasty or brow lift is performed via scalp incisions either endoscopic or open via a coronal incision.