When the layer of oil in the hair is broken down, the moisture trapped below evaporates, leaving the hair to dry out and become more prone to damage. It isn't long before you end up with dry, unmanageable areas complete with split ends and broken shafts. You should wash it as infrequently as you can and use a mild shampoo with a cream conditioner afterwards. Leave the conditioner on for a few minutes before rinsing. Don't brush your hair out too much, try to comb it gently.
Dry hair is fragile hair.
The good news about hair is that it is programmed and designed to battle the elements. The cells in your hair shaft's thin outer layer, or cuticle, overlap like scales to protect the shaft's inner mass of fiber, called the cortex. The bad news is that you're in a constant state of combat with the environment. Sun, salt and chlorinated water draw moisture from the hair, strip away the sebum and damage the cuticle of the hair. If the cuticle scales crack or warp, the roughened hair surface loses its natural sheen and the fiber of the cortex frays, creating frizzy, dry hair.