Head skin is full of dandruff. For this.

Hi ! Dandruff is a chronic condition that comes and goes. It is due, in part, to a yeast that lives in the scalp. There are many effective treatments including shampoos made of : ketoconazole selenium sulfide zinc pyrithione  You can use a ketoconazole containing antidandruff shampoo like “Scalpe”after washing scalp with your regular shampoo thrice a week for a month and then as maintenance at least once a week for 2 months.You need to leave the product on for 5 to 10 minutes prior to rinsing.  This will help to control the yeast responsible for dandruff. Avoid hair styling products and gels on scalp. Do not keep scalp oiled for long time. Do not share combs etc. Air dry your hair. Avoid using hair dryers. Do not scratch or itch.

Refer"Understanding Dandruff" by Dr. Jolly Shah Kapadia - https://www.practo.com/healthfeed/understanding-dandruff-8830/post