@UnicornsReal
My grandmother was also convinced that washing your hair whilst on your period would cause a chill. Her sister died when she was 17. She just dropped dead apparently. My grandmother was convinced it was because her hair was wet that day to hair washing. Women had waist length hair in those days and there was no central heating.
Also shared baths as people mention.
My grandfather had the view that children shouldn’t be allowed to play in the snow on case they got chilled. He also thought if people didn’t wear slippers indoors they would get ill.
So many children got fatal illnesses at one time, in unheated houses with not enough clothes or proper shoes. Keeping warm was probably very important in reducing the chances of fatality ir serious illness.
No hairdryers then either.
I think we are very spoiled in terms of the ability to get warm, so we don't realize that some of these things may have had some valid reasoning behind them, even if people's understanding of the mechanisms weren't quite right. With central heating, and even things like modern fabrics for clothes, it's just a different kettle of fish.
If you go up North here in Canada to where the Inuit live, children there are taught that if they are out playing in the winter, and they start to sweat, they should stop running around. Getting sweaty means potentially getting cold and not being able to get warm again.
By the late 60s of course things were changing, but memory usually goes back two generations. The parents of kids in the late 60s would have been born in the 30s or even earlier, and the grandparents could have been Victorians. And parenting was still much more done according to the way your parents and neighbours did things.