Concealer is the most valuable product on a mature face and the one most likely to go wrong. Valuable, because targeted coverage lets you wear a much lighter foundation — which is the single biggest improvement available to most people over 50. Likely to go wrong, because the place it goes is the thinnest skin on your body, sitting on top of a muscle that moves every time you blink.
Everything about the under-eye works against a cosmetic product. The skin is roughly a third the thickness of the skin on your cheek, so it holds less moisture and creases more readily. The orbicularis muscle contracts constantly. And the area is slightly concave, so anything that moves has a low point to move into. A concealer that sits beautifully for an hour will have gathered in a line by lunchtime unless the quantity was right.
Quantity is the main variable, not formula. Almost everyone applies two or three times as much concealer as they need, across a far larger area than needs covering. The actual shadow under most eyes is a crescent in the inner corner and along the tear trough — not the whole area from lash line to cheekbone. Covering the whole area with enough product to hide the darkest part guarantees creasing everywhere else.
The category divides by what you are covering, and the distinctions matter. Under-eye shadow is a blue-gray discoloration best treated with a peach- or pink-toned corrector under a thin concealer. Age spots are discrete brown marks that need a matching-tone concealer placed on the spot, nothing more. Crepey skin is a texture problem that concealer makes worse, not better — less is the only answer. Redness is a color-cancellation problem, covered on the rosacea page.
Price buys shade range and texture refinement. At the premium end you get genuine depth and undertone coverage — which matters more for concealer than foundation, because a mismatched concealer leaves a visible pale patch — and formulas that stay flexible for longer. At the drugstore end the most useful thing you can buy is an oversized applicator, which means fewer strokes and less blending on skin that does not enjoy being rubbed.
The mistake to avoid is setting heavily to stop creasing. It is the standard advice and it is backwards: powder in a fine line makes the line more defined, so a heavily set under-eye creases into something more visible than it would have unset. A very small amount of a very finely milled powder, pressed on, is the most that helps — and should you set concealer with powder covers when to skip it entirely.