Look up the actual mandate and read it. In PA there are a number of reasons that can exempt you from wearing the mask and the mandate specifically states you don't need to provide documentation (as this would be a HIPAA issue in many cases). I have printed copies of PA's mandate with the appropriate sections highlighted in case anyone wants to be a dick about it (I'm a disabled vet with a legit lung condition) and I just carry that with me. It's staggering how many people don't actually know anything more than the headline they read saying "it's mandatory", but they'll approach me and make a scene even though they couldn't be bothered to read the shit.