What evidence would there be that people had (or didn’t have) acne in prehistoric times? They wouldn’t have left any written evidence or popping videos, or anything like that. Not every culture has a tradition of realistic portraits (and some of those that do would deliberately leave out something like acne). I suppose there could be tools for popping pimples, but could we be sure that was how it was used? People can pop pimples without specialized tools, so a lack of those tools wouldn’t necessarily mean that there was no acne.