p00h, I told my mum that not washing hair is damn disgusting. & the logic is that they dun want use to catch a cold or get 'wind'. So as long as no cold water, no cold air, wash hair is ok what.
& my mum agreed. Thankfully, my mum quite modern one. Will listen to what I say also.
e.g. I told her cannot put cereal in milk cos baby might choke, she said last time we also brought up like that. I just tell her, be thankful I am still alive cos I din get choked, so I'm not gonna risk it with my kid. Then she just follow & nvr mention already.