Severe dandruff that does not improve with shampoo can be due to a strong scalp infection, excess oil, or conditions such as seborrheic skin changes. Wash regularly, leave the shampoo on for a few minutes before rinsing, avoid heavy oils, and keep the scalp clean and dry. Try to manage stress and maintain a healthy diet to support scalp health. If there is still no relief, consult a doctor to check the scalp and guide stronger or targeted treatment.