It is not necessarily bad to wash the hair everyday, but doing so has very little benefits. Most professionals suggest only washing the hair three or four times per week.
The more the hair is washed, the worse it can look due to the washing away of natural oils. Longer, thicker hair can go longer between washing. Some people suffer from oily hair, and this may require washing more often. When dealing with oily hair, users who wash daily should use a lightweight shampoo. Using dry shampoo or baby powder in between washes can help absorb oils, which helps to prevent a greasy look.