Bryan, never had a reaction before, so yes it was a concern.
I use a

THERA-P-RELIEF reuseable cold and hot compress (the one in the photo to the right). I keep it in the freezer. Possibly my mistake is I didn't put anything between my skin and the compress. Warm leg did not like cold pack? I didn't have anything on my skin before or after the run, just the icy compress.
It felt great and did the trick otherwise.
Thanks,
Nancy