There has been a global rise in young women developing tic-like behaviour during the COVID-19 pandemic.
A sociologist said the trend, commonly known as 'TikTok tics', is a phenomenon caused by social media that is showing similarities to the Salem witch trials.
Sociologist Dr Robert Bartholomew, an expert in mass psychogenic illness, told AM the tics are a form of mass psychogenic illness which is a nocebo effect or "placebo effect in reverse".
It's when people in a group start feeling sick simultaneously even though there is no physical or environmental reason for them to be sick.
But the 'TikTok tics' are a rare form caused by prolonged stress.
Dr Bartholomew said the COVID-19 pandemic caused a large amount of anxiety and disrupted people's routines.
He said the stress coupled with people sharing their experiences with Tourettes on social media sites like TikTok saw young women develop tics.
While teens experiencing sudden-onset tics do not have Tourette syndrome, the characteristics of the tics are similar.
"This is the same phenomenon that happened during the Salem witch trials of the 1690s. It's just manifested in a different form," Dr Bartholomew said.
The Salem witch trials are an infamous case of mass hysteria where young girls started experiencing "fits" and were accused of being witches and some were executed.
"Under that prolonged stress the nerves and neurons that send messages to the brain get disrupted, so you get twitching, shaking, altered states of consciousness."
And it is more common than people realise.
Dr Bartholomew has collected around 35,000 cases of mass psychogenic illness dating back to the Middle Ages and found 99 percent were female, with the number one group affected being young women around puberty.
University of Edinburgh Professor of Neurology Jon Stone believes the tics are a functional neurological disorder causing involuntary rapid and repetitive movement and sound.
Prof Stone wrote in The Conversation such symptoms have been disbelieved by health professionals in the past and stigmatised under labels like "hysteria" which is one reason why they have remained so hidden.
Researchers are divided on whether social media is the cause of the sudden tics in teenagers or one of the many potential risk factors.
But Dr Bartholomew said the potential consequences of the role social media plays in spreading mass psychogenic illness are alarming.
"Social media seems to be the common denominator here in spreading these. In the past it's usually confined to a small group, usually a classroom or a year level, now it's spreading throughout the schools and throughout communities," Bartholomew said.
"The danger here is in the past you've had these cases that are self-limiting but because we've got now social media you've got thousands of girls around the world picking up these tics."
His advice to parents is to monitor their children's social media and limit their time on screens.
