1. What the Nasolabial Fold Actually Is, and Why It Deepens
The nasolabial fold is not a wrinkle. It is a boundary, a fixed line where the skin is tethered down to deeper tissue between the cheek and the upper lip. Everyone has one at every age, and a face with no nasolabial definition at all does not read as young. It reads as flat.
What changes with time is the tissue on either side of that boundary. The deep fat compartments of the midface deflate and the bone beneath them remodels, so the cheek loses the platform holding it forward and upward. The more superficial fat then travels downward and gathers against the fold, because the fold is where it is anchored and cannot go any further.
That is why the groove appears to deepen even though nothing was removed from the groove itself. It is a shadow cast by fullness now sitting above it and by the hollow left where that fullness used to be.
A second mechanism runs alongside the first. Decades of smiling crease the skin along the same line, and repeated folding gradually etches a fine line into the dermis that stays visible at rest. Most people arrive with some of both in different proportions, and separating them is the whole of the assessment.