Look at the active ingrediant on some dandruff shampoos. Get like 3 diffrent kinds. Use one kind about 3-4 times per week. Then stop till it comes back, basically just repeat process but use a diffrent one.

Using a diffrent one will keep your skin from building up an immunity to the active ingrediant.

I've had dandruff all my life. I have to use strong stuff, every day.

Head and Shoulders. Mid line.
Selsun Blue. Mid line.
Walmart special. Low end.
TGEL. Higher end but smells kinda bad.
Nizoral. Great stuff, but can get temporary immune too quick.