We get this question asked all the time. You can wash your hair as often as you like, but keep in mind you are washing away crucial oils that lubricate you hair. Here are some pointers:
If your occupation/after work activities has high dirt levels (landscaper, construction worker, farmer, sports) go ahead and wash, but use a conditioner every other day to keep your scalp conditioned.
Normal Activities-Every other day is fine
Fine hair-Every other day is good, but if you need to do every day, use a shampoo with no sulfates and low lather. High lather doesn't mean its cleaner. Condition every 2 shampoos, unless your hair is dry or color processed.
Curly Hair-3 times a week. Curly hair has a tendency to be dry. Your natural oils coat the hair. Using conditioners designed for curly hair add more moisture. If you have thick curly hair, use oils sparingly at the scalp area and focus more on the midshaft to the ends.