To add to this...
Saunas and ice baths don't damage cells but actually have benefits. Don't quote me as this is a rephrase that makes it sound like bro-science, it actually activate some heat shock proteins and also leads to hormone release.
Better, sound science can be sourced from Dr. Rhonda Patrick a la Tim Ferriss podcast or Google Scholar
Core temperature is tightly regulated, as well. It should be 37degC. Plus or minus just 2 degrees will severely impair function, plus or minus 5 degrees is reason to call 911.