Thank you for the photo. A dark or hollow circle under one eye at 48 usually comes from one of three things, and often a mix. The first is volume loss or a tear trough hollow, where fat and cheek support descend and leave a groove that casts a shadow. The second is a bulging fat pad above the hollow that creates a bag, making the groove look deeper. The third is pigment or thin skin that lets the blood vessels show through, which looks blue or brown. The fix depends on which one dominates. A hollow without a bag often does well with a small amount of hyaluronic acid filler placed deep by an experienced injector, or with fat transfer. A true bag with a hollow is best treated with a lower blepharoplasty, either transconjunctival fat repositioning, which moves the fat into the groove, or fat removal when there is little hollow. Pigment is treated with topical brightening agents, peels, or laser. Because it is only one side, asymmetry in cheek volume or lid position is also worth checking, since correcting that can reduce the shadow on its own.