A reasons for skin of head dryness are..

As a bad meal, poor selecting an items for hairs care, use many of gel, mousse, spray, as oily balsams, milk of, kefir,creamy will save you, eat healthy.
And  dandruff display after a foreign brush, or comb.
A dandruff is a condition as happening in an internal of organism, and reasons are internal.
Dandruff is not contagious.
An often washing will worsen this process.
Good shampoo selecting, and rinse good will not worsen this, use a soft shampoo without a chemo substances,so as a few shampoos are hard minerals and other substances and damage hairs, the rinse head with cool water.

Comb her will remove her.
A very good to wash often hairs, and care shampoo using, in dandruff,irritated skin as you shampoo is calming effect with and for frequently use, do not scratch a skin of a head.

Rare having a dandruff in children, and dandruff meeting in 20 y, old or older.