If you're an adult, there's a good chance your itchy scalp is resulting in dandruff -- oily, dead skin flakes that fall from your scalp. Some cases of dandruff are mild and can be fixed by simple changes to your hygiene regimen. Infrequent hair washing, for example, lets oil and dead skin cells accumulate, which can result in flakes, while overwashing can strip away oils and cause itchiness.
There are also several skin conditions that can cause dandruff, including seborrheic dermatitis, psoriasis and eczema. A new hair washing routine won't do the trick in these cases -- a trip to a dermatologist to discuss treatment is a better bet.