Why does the electric baking pan dye the surface of food black? Is it harmful to health?

The black stuff is cooking oil and the residue left over from previous baking. After carbonization, it will turn black and stick to freshly baked food. It doesn't have much impact on health, but for the sake of beauty and healthier requirements, it is recommended to wash it carefully after each use and rub some cooking oil after cleaning, which will be better next time.