If the fold shows even without smiling, filling does improve it.
A nasolabial fold is a crease that forms as cheek volume settles. Filling under the fold with hyaluronic acid lifts the hollow so the crease shallows and the shadow softens. If cheek sagging is the real cause, filling only the fold can look unnatural, so it is often approached together with cheek volume.
One session lasts nine to eighteen months, varying by product. The mouth area moves with speech and smiling, so it absorbs faster than the mid-face. Placing it in a relatively deep layer beneath the fold lasts longer than shallow placement, so the depth also changes the duration.