This is one that I've heard on more than one occasion: "Don't wash your hair every day. Wash it every two days as washing it too often will damage it."
Is there any truth in this?
Can frequent hair washing cause hair loss?
The only information I could find on using shampoo too often being bad for your hair is the sebum (oil) produced by the sebaceous gland.
When you ask if your hair can get used to not being washed you’re implying that leaving oil on your hair will somehow stop the production of more oil. The flip side of that implication is that stripping away the oil with a shampoo will make your glands produce more oil. Well guess what. That’s exactly what DOES happen. Sort of.
Their* data indicates that the presence of oil on the skin’s surface sends a signal to the sebaceous glands to turn off. This signal is caused by either the pressure of the oil in the follicle or by the creation of a chemical signal that travels back down through the skin. So it turns out that, in theory, you can “train” your hair to be less oily. * http://www.springerlink.com/content/pv373302mt827067/
So basically washing your hair with shampoo to often can lead to more greasy hair and more frequent washing.