Speaking of wet hair damaging your health... when I was a kid I was told that I would go blind if I went to bed with wet hair. I'm not exactly sure where that belief comes from but I'm guessing it's because when wet hair gets onto your eye, there could have a higher chance that you'd end up producing more eye discharge/mucus. And when eye discharge/mucus solidifies while your eyes are closed.. well, let's just say it really hurts just to take off all that crusted eye buggers.
As absurd as it may sound, I have to admit that I even had to have my eyelid operated just because I wasn't able to get rid of all that before it turned into a minor infection. (Though me going to bed with wet hair actually had little to nothing to do with that)