So what’s the deal with trigger warnings? Do they actually help? They clear are a culture war fixture. But where do they come from and is there any scientific evidence behind them?

Because they first got public attention at liberal arts universities in the US I assumed that it was the popularization of academic research. That’s not actually what happened. It was students who pressured schools to adopt them. Where did the students learn about trigger warnings? Early social media! LiveJournal, Tumblr, and most especially fanfic sites had trigger and content warnings on their content and lots of students had used those sites in high school and liked the idea of trigger warnings. 

Search Engine is a great podcast, and they did an episode about the origins of trigger warnings. 

https://www.searchengine.show/listen/search-engine-1/what-do-trigger-warnings-actually-do