I hear every conceivable answer to the question of washing ones hair. Should it be done daily, twice a day or weekly?
A famous hair researcher recently suggested that a wool sweater of the highest grade, if washed everyday for a year, would eventually show significant wear and tear after a year. That is because the soaps and detergents used would break apart the wool fibers with time. Better wools stand up to the detergent attacks better. So it is with hair, more washing eventually damage the hair over time as the wax that protects the hair shafts (sebum) is washed out. The shorter the hair, the less the problem as the older hair (ends of the hair) show the damage of washing over time much more than short hair. Women with long hair complain of ‘split ends’ often and this is the result of accumulated washing and drying of the hair. Blow dryers produces more damage to the hair.
For most men who do not let their hair grow to shoulder length, wash as often as you wish. Use good quality shampoos and if you add a conditioner, it will re-hydrate the hair shafts after the detergents take out the wax that normally protects the hair.