Why never? Three or four weeks will be enough to earn yourself a whole bunch, up to terrible dermatitis and psoriasis.
But if you wash your hair only with water, without cosmetics, it can only be beneficial. Especially if you have problems with oily hair. I'll leave a link to our detailed article on this if you're interested in reading more. By the way, we also wrote about the consequences of an eternally dirty head
I don't know how about never, but I can say about the year. Long patched and curly hair. It itches at times. Greasy and smells like in a chicken coop (according to friends). Otherwise, nothing unusual.