He has to wash his hair daily due to dandruff issues.

dandruff 是名词，指"头皮屑"，由头皮脱落的死皮细胞组成，通常呈白色或灰色片状。这个词由 dand（古英语词根，表示"头皮"）和 -ruff（可能来自 rough，表示"粗糙"）组成，字面意思是"粗糙的头皮物质"。