having thin hair; thinning hair
Describes a person whose hair is naturally thin or has become sparse. Often used euphemistically. Compare with 髪の薄い, which is a noun-modifying form.
See also: 髪の薄い
My father has had thin hair since he was young.
Lately I feel like my hair has been thinning.
Phrase composed of 髪 (hair) + が (subject marker) + 薄い (thin). The meaning is transparent from its components.