Was there a specific era that caused widespread acne for teenage humans? Or have we always had it?
Note: If this post belongs on r/askscience let me know and I’ll go there. I’m more interested in the historical relevance of acne than the biological manifestation.
Humans do appear to have had acne prior to the Industrial Revolution and its manifestations were linked to what we now call puberty -- sometimes in historical sources this means beard growth for males (at least as far back as Aristotle) or the development of sexual desire in adolescents, and is said to diminish after marriage several years later. In the modern era acne doesn't always disappear after a certain age, but that at least bears a resemblance to the modern casual understanding of acne as a phenomenon coinciding with adolescence and terminating in the late teens and early twenties. I have an earlier answer about pre-20th century acne and skincare here that links to a couple other answers about the history of acne -- I can't speak to whether historical environmental conditions have influenced the appearance of acne over the years (though I'd love to know if anyone at /r/askscience has any leads) or if it's grown more prevalent but acne itself has a fairly long pedigree.
(On a side note: I've noticed a couple pre-20th century writers refer to the removal of worms from the skin as a common aspect of skincare, including in contexts where it seems doubtful that they're really talking about topical parasites -- Jonathan Swift's Celia squeezes out "worms" from the skin of her nose with the aid of her vanity mirror in the amazingly gross The Lady's Dressing Room for instance. I suspect this describes something more like sebaceous filaments squeezed out of pores, rather than a commonplace infestation of tiny face worms. But I'll have to hunt down more references and see if there's already scholarship out there.)