Quote Originally Posted by Righteousbabe
I get the same rash. It is right at the shorts line on the tops of my legs. I only get it in the hotter summer months on my long rides. The last couple summers I just dealt with it. But this weekend my rash was worse than usual (huge, raised welts and tender to the touch). So I decided to see if I could get in to the dermatologist on Monday. He took a look at it and I described how it only happens during my long, hotter rides. That I have tried everything I could think of (different sunscreens, different laundry detergents, rolling the shorts up higher, etc) but I still get it on the same spots on the legs. He thought that it was the chemicals in some of the sunblocks, and suggested a titanium dioxide sunblock. I told him I have tried that already and it does not make a difference. He was stumped. So he just prescribed a strong steroid cream and said if it does not go away or gets worse, come back. If he has no idea what is causing it, I do not know why I should go back...

So...I have decided it is some type of heat/sun rash and I will just have to live with it. If anyone else goes to the doctor and actually finds out what it is and has any suggestions, please let me know!

See...this is exactly what I expected to hear from my derm! (I never went because I think I've figured it out...)

Based on some experiments I did...I've come to the conlcusion that the welts are hives brought on by overheating. It's not really a heat rash in the traditional sense, but it's definitely from the heat. A few weeks ago we were on a 75 mile ride and right at about mile 45 or so, the heat got intense (we'd left late so it was mid-day right when we hit the farm land....no shade). It was well over 100 degrees on our bike computers and I just wilted. I felt it come on with a slight tingling in my whole body and sure enough, I glanced down and the hives were appearing. It was a very rough ride and while I was amazed at my ability to stick it out, it did a number on my legs. Those hives took DAYS to go away and now, 3 or 4 weeks later, I still have the discoloration from them.

The good news is that on our next long ride (78 miles), I ran a little experiment. I knew that our planned ride would take us by plenty of stores, so I could be liberal with the water. I carried extra, wore a ton of it, drank more than usual, and did everything in my power to keep my core temp down. I was dumping it on my head and my back almost the entire ride. It worked..it was just as hot for that ride as it was for the other one (and the second one was even more hilly) and I felt good the whole time AND saw no hives. They were kept at bay!!

For me, it's definitely heat-induced and not just leg heat...but core body temperature heat! I'm just happy that I now know how to control it.