“My mom used to tell me, growing up, to never go to bed with my hair wet. Because that is the cause of you getting sick. But I’ve never gotten sick after going to bed with wet hair. In fact, I do it a lot.”
My informant immigrated from Shanghai with her mother when she was five years old. The idea that going to bed with your hair wet could make you sick seems to be a common one among immigrants, as most children of especially Asian immigrants that I interviewed told me the same thing.
Many Asians still rely on traditional medicines, and so it makes sense that they would have traditional folk beliefs about getting sick to accompany this reliance. Especially before industrialization, a cold could turn deadly; any methods of prevention were likely taken, even if they didn’t necessarily make sense. The belief that wet hair makes you sick is likely a holdover from those days; the belief has been passed down through the generations so that, even though we now know that wet hair is unlikely to make one sick, it is still a persistent belief in many cultures.