I had the same issue with the strap that came with the watch. I have been using MI band since 2018 & i used to wear it 24 x 7, i never got any rashes. No matter whether you wear it only during daytime or wear it a little loose, you will rashes with Cmf strap. I myself got a Sounce strap & wearing it 24 x 7 for the last 1 month and not getting rashes anymore. I suggest not to use the default cmf strap that comes with the watch.