Severe dandruff is often due to seborrhoeic dermatitis, which is caused by a yeast-like fungus on the scalp rather than a serious infection. You can try using over-the-counter anti-dandruff and antifungal shampoos containing ketoconazole, selenium sulphide, or zinc pyrithione, 2 to 3 times a week, leaving it on the scalp for a few minutes before rinsing. Keep your scalp clean and avoid applying heavy oils or hair products that can worsen the condition. If it does not improve within a few weeks or becomes severe, it is best to consult a doctor or dermatologist for stronger treatment.