I get headaches while riding and I think I figured out the reason, but I just wanted to run it by you folks and see if you've ever heard of anything like it. My headaches (pounding right between my eyebrows, always) generally happens when I'm mountain biking or riding around urban areas and less while road biking, where I sweat less and I stay "cooler".
Anyways, I think it is either my helmet being too tight or my hair growing too long (also causing aforementioned tightness of helmet) and preventing heat from evaporating in the form of sweat. I haven't had a hair cut in quite a while so my helmet has been getting tighter and sweat doesn't evaporate as fast. I also noticed that my headaches are worse under the sun and it subsides almost immediately when I take my helmet off, loosen it or pour water on my head.
Should I worry about other underlying causes, or are headaches common with a hot head getting squeezed by a helmet? I'd rather not go get a haircut and not feel headaches anymore if they were warning me I have some kind of brain tumor or something even though that is unlikely since I'm 19.