How typing polishes a keycap
A new keycap often has a fine, slightly rough texture molded into its plastic surface. That texture scatters light in many directions, so the key looks relatively matte. Each press also slides a fingertip across the key. Over time, this repeated contact wears down tiny surface irregularities, leaving the most-used spots smoother. A smoother patch reflects light more uniformly, which is why it appears shiny.
The change is gradual and uneven: frequently used keys such as the space bar or the letters in common words can develop glossy centers while nearby keys remain dull. The shine is a record of where fingers land, not simply a sign that the keyboard is old.
Why the surface looks greasy
Fingers leave behind skin oils, along with traces of sweat and dirt. Those deposits can make the key look slick and may add a temporary sheen of their own. They also collect more visibly in the shallow texture of a keycap. Cleaning can remove much of this residue, but it cannot restore texture that has been worn smooth.
That difference explains why a cleaned keyboard may still have bright, polished-looking patches: the oily film is removable, while the altered plastic surface is not. The gloss maps both the repeated motion of typing and the places where the original texture has been rubbed away.
