Unhealthy; in poor health or having habits/conditions that are bad for health.
不健康な食生活を改めたほうがいい。
You should change your unhealthy eating habits.
夜更かしが続くと不健康になる。
Staying up late repeatedly will make you unhealthy.
彼の顔色は不健康に見える。
He looks unhealthy (his complexion looks poor).