I always ride with a full face helmet, gloves, and boots. I usually wear a jacket, but will admit that when the temperature gets above 95 degrees I won't wear one. Where I live (Dallas/Fort Worth area) the summer heat can be hell, but our winters can be heaven! You can usually ride all winter long. On a side note, for the people who live up north, they usually say that their temperature gets just as high as it does down here (100+) and that is true. The difference is that it only gets above 100 up there for maybe a week or two at the most. I have seen summers here where the high temperatures stayed 100 or above for 45 days straight. And it isn't a dry heat! The lows will be in the lower 80's at the wee hours of the morning! My wife and I went on a bike trip where we planned to be at our stopping destination by mid-day each day of the trip. So much for plans, one of the days we had some delays getting away and ended up riding about 200 miles with the shade temperature of 115. I found that the full face helmet actually insulated my head from the heat. It also helped that they were white helmets.
I know that riding without all the gear is not wise, so I will just have to only ride when it is not so hot. As the rider who lives in Arizona can attest to, it is not a matter of just sweating in protective gear, the heat can endanger you life! Heat exhaustion and Heat stroke should be taken seriously!