I don't know what causes dandruff, but I know an effective home remedy to get rid of it.

It involves washing your hair with table salt.

The next time you're going for a hair rinse, take a container with a couple table spoons of salt in it.

Put the salt on your hair and scrub throughly. Repeat once or twice and rinse when you're done.

Do this and you should be able to get any dandruff of your hair.

I'd recommend waiting a day or two after getting a haircut before you do this. As the salt can cause Irritation to sensitive skin.