Two lip products can look identical and behave completely differently through a meal. The distinction lies in whether the colour is resting on the lips or attached to them.
Conventional lipstick is a suspension
A classic bullet lipstick is pigment suspended in a blend of waxes and oils. The waxes give it structure and the oils give slip and comfort.
None of that binds to the lip. The film sits on the surface, held only by its own tackiness and the shape of the skin beneath it.
Anything that touches it takes some away, because the oil and wax transfer readily onto cups, cutlery, skin and fabric.
Long-wear formulas rely on a film former
Transfer-resistant products replace much of the wax and oil with polymers dissolved in a volatile solvent that evaporates after application.
As the solvent leaves, the polymers form a continuous flexible film with pigment locked inside it. The film adheres to the lip rather than resting on it.
This is why these formulas feel wet on application and set within a minute, and why they cannot be blended or adjusted once they have dried.
Stains work at a different depth
A stain uses dyes rather than, or alongside, suspended pigments. Dyes are soluble and can penetrate slightly into the outermost cells of the lip surface.
Because the colour is in the surface rather than on it, there is little to transfer. What remains visible is the tinted tissue itself.
Colour therefore fades as those cells shed rather than as the product rubs off, which produces a gradual softening rather than patchiness.
What the trade-off costs
The polymer film that resists transfer also resists moisture moving in either direction, which is why long-wear formulas are associated with dryness.
Removing them requires an oil or a dedicated remover, since water and ordinary cleansers do not break down the film efficiently.
Dyes are similarly persistent and can be difficult to remove from the vermilion border and surrounding skin if application was imprecise.
Why the categories are increasingly blended
Many current formulas combine a film former with emollients that sit above it, aiming for the wear of one category and the comfort of another.
Others apply as a stain and are topped with a separate balm, which restores comfort without disturbing colour that has already bound to the surface.
The behaviour of any given product is therefore better predicted by how it applies and sets than by what the packaging calls it.