How Cetrimide helps dandruff?

Cetrimide is known to have antiseptic properties that kills bacteria, fungi, and viruses that inhabit the skin. Besides that, it can remove debris and dirt from the scalp via its detergent-like properties.
Due to its multi-action functions, it can be utilised for many conditions of the scalp ranging from oily, psoriatic to itchy scalp.

As an application topically, it should be used 2-3 times a week on wet hair. The scalp should be massaged gently with fingertips. A thorough rinse is important followed by repeat in the application as necessary.

References:
http://www.pharmacygeoff.md/Cetrimide_Shampoo_Cetrimide_20_100mL_Bottle_p_1204.html