In many states its illegal and also it impairs your ability to see ahead by a percentage especially at night or inclement weather. Its not going to be sunny 24/7 and its not gonna be sunny every day. Just get good polarized sunglasses its like tint you can take off. Did wonders for me.
On top of that you would have to get a notice from your doctor that you are at high risk for skin cancer and then submit that to your DMV for your exemption sticker (Prevents harassment from the police and in states where inspections are done, they will still pass you).
Yeah, and you are not going to get skin cancer from sunlight going through the glass. Glass is naturally effective at blocking UV rays. It blocks a lot the UV B and C, and it converts UV A to infared. If that is a serious concern, you could wear sunscreen all the time.