No. It really seems to be the hot sun. We keep the house warm for my mother-in-law. And while that has me spending more time in my cool basement office/study, it's not oppressive like biking or walking out in the hot summer sun. For the last few years I use sun sleeves and a skull cap under my helmet and that helps. Part of that is being at a higher elevation where the heat from the sun can really be felt. But in my first 20 years here in Colorado I could ride all day in the hot sun without any repercussions (other than sun-burn).