Persistent dandruff despite shampoo is often due to ongoing scalp fungus, excess oil, or an improper routine, which can cause it to return. Wash your hair regularly, leave the shampoo on the scalp for a few minutes before rinsing, avoid heavy oils, and keep your scalp clean and dry. Manage stress, eat a balanced diet, and avoid scratching to prevent worsening. If it keeps coming back, consult a doctor to adjust treatment and control it long-term.