I have the same problem. Texas is so dang hot that it's sometimes hard to even want to go out and ride. I get up at 6am so that I can ride before it really starts to get hot because I have the same problem as you. My head's always been the hottest part of my body. A new helmet with better ventilation might help you. Also, if your helmet doesn't have a visor, it actually does help. I wouldn't wet your hair because it seems to me that when I go outside on a humid day without blowdrying my hair, it just makes me that much more miserable, so it might actually make it worse. YMMV. The ice water might help, though if you stay out for longer than an hour or so, it might get warm anyway.
It sucks, but it's something your body will eventually kinda acclimate to and it won't seem so bad after a while. Good luck.
It sucks, but it's something your body will eventually kinda acclimate to and it won't seem so bad after a while. Good luck.