Overlining is a lip liner technique that draws the outline a millimetre or two outside the natural edge of the lips, so the lips look fuller without filler or a visible change of colour.
Also known as: overlined lips, overline lips, overlining lips, lip overlining
Overlining works because the eye reads the outer edge of colour as the edge of the lip. A liner close to the natural lip shade, drawn just beyond the vermilion border and blended inward, adds visible volume while the skin outside the line still looks like skin. Douglas gives the same measure for Dutch readers: one to two millimetres above and below the lips, then blend inward (Douglas).
Placement decides whether it looks natural. Makeup artists Ehlie Luna and Alexandra DiBlasio advise keeping the exaggeration subtle and around the cupid's bow, using short vertical strokes on each peak, then connecting to the natural fullest points at the sides. On the bottom lip, overline only the centre. Extending the lower line into the corners creates a downturned smile (Marie Claire).
The liner shade matters as much as the line. A colour one to two shades deeper than the natural lip, or matching it, blends into the lip and hides the border. A liner much darker than the lipstick shows the overline as a ring. Blending the inner edge with a brush or fingertip before adding gloss or lipstick stops a hard line from showing through.
Overlining also corrects asymmetry: thicken the line only on the smaller side, and build height at the cupid's bow on wide, flat lips. Full lips gain crispness from a line on the natural edge and need no extra width (Who What Wear).