I get them, too, and at first I though they were related to the shorts elastic...or the detergent I used to wash my clothing with. But it turns out I get them regardless of whether the elastic is rolled up or not....or what type of detergent I use. I even went to the dermatologist to get his input, and he had no idea and gave me a Rx for hydrocortisone cream. I tried using it after the rides...but with very minimal relief. For myself, I think it is directly correlated to heat/sun/core body temps. (there was a posting last year here on the forum where we discussed this before). I don't get them when the temps are below 90 or when it is mostly cloudy. But when it is hot and very sunny, that is when I get them.

I have just learned to live with them. I don't like it because it is ugly and even a little painful at times, but I have not found a way to avoid getting them during the summer.