What is the white powder on the white edge of the ceramic cup cover?

I bought a ceramic cup with white powder on the white edge of the lid, which may be the glaze on the ceramic cup.

These powders may be stains caused by long-term contact with hands or mouth, or tire soil worn off by the friction between the lid and spout of porcelain such as cans and pots with lids. These white powders generally have no effect on human body and can be used normally.

If the cleaning requirements for ceramic cups are very high, you can brush them with steel balls or gently polish them with fine sandpaper, and then rinse them with clean water.