This depends on the following list of factors.
•Hair type (straight hair and curly hair need to be washed differently). Hair that is thicker and curlier can go without a wash for a longer period than hair that is more fine.
•There can be too much of a good thing. Washing hair everyday removes our natural oils and proteins, causing the hair to dry out quicker. Shampoo strips the oils from the hair, and we need those oils to help our scalp and hair to be healthy.
•Find the perfect shampoo. These should balance your scalp and hair so that one can wash every third or fifth day. For fine hair, shampoos that increase the hair in volume should only be used as this would avoid the hair from getting greasy quickly.