Thanks for the query. Severe dandruff could indicate dandruff itself which is significant or can indicate beginning of some other skin condition like Seborrheic dermatitis or Scalp psoriasis. So consider discontinuation of oils and using an antifungal shampoo everyday for first week and then reduce the application to twice a week for maintenance. You should keep the shampoo at-least for 5 minutes on the scalp for it to act. This should solve your problem. kindly consult a dermatologist for exact diagnosis and treatment plan. It is also important to prevent their relapse once you have got it cured.