University students are being warned when classes contain graphic or sensitive content, including sexual abuse, rape and transgenderism, to protect their mental health.

Australian academics are issuing so-called "trigger warnings" for confronting material in classrooms at the start of each semester, and before classes, to give students the chance to opt out.

Dr Lauren Rosewarne and other academics are using 'trigger warnings' in class. Credit:Penny Stephens

The warnings - aimed to avoid triggering a post traumatic stress reaction - have stemmed from trends in online chat forums and blogs, and has expanded to universities in the UK and the US, but have sparked a backlash in Australia.

University of Melbourne's Dr Lauren Rosewarne, who teaches about gender and sexuality, has been warning students about potentially disturbing content since she started teaching 13 years ago.