noun
blackhead
Specifically refers to a blackhead (comedone) on the skin, often in skincare contexts.
鼻の黒ずみが気になる。
I'm bothered by the blackheads on my nose.
noun
dark discoloration; blackening; tarnish
General term for dark staining or discoloration on surfaces, metal tarnish, or soot-like marks.
銀のアクセサリーに黒ずみが出てきた。
Dark tarnish has appeared on the silver accessory.
壁の黒ずみはカビかもしれない。
The dark discoloration on the wall might be mold.
黒ずむ is the verb meaning 'to blacken' or 'to become dark/discolored'; 黒ずみ is the noun form referring to the resulting stain or blackhead.
Noun form of the verb 黒ずむ (to blacken), from 黒 (black) + ずむ (a suffix indicating a state or tendency).