Social media trends that encourage young people to pull high-risk stunts have parents shaking their heads — or seeking help from police and doctors.

The latest, Game of 72, challenges teens to find ways to disappear for three days. It's enough of a concern to prompt police in the U.K. and parts of Canada to issue warnings.

Read on for some other risky social media challenges or trends that have a teen following.

The choking game

Baby boomers will recall this as a schoolyard game they took part in years ago to experience a temporary high. The difference now is that young people can find instructions on the internet and some are playing the potentially deadly "game" themselves. The fleeting, euphoric feeling comes from lack of blood flow to the brain.

The cinnamon challenge

YouTube

Taking the cinnamon challenge could leave you with a collapsed lung and scarring because of the cellulose fibres in the spice. (YouTube)

In this prank shown on YouTube, participants swallow a spoonful of ground cinnamon in 60 seconds without water. It's an excuse to film your friends coughing, making faces and spitting out an orange cloud of dust. Doctors warn that gulping the woody fibres can cause excessive inhalation of cinnamon particles and lead to a collapsed lung.

Salt and ice challenge

With any luck, this trend will stay locked in the social media vault after a Pittsburgh boy "burned" a cross into his back in 2012 by holding ice to a layer of salt on top of his skin. YouTube videos instructed young people to "get burned" by holding the ice in place for as long as possible. Adding salt can drop the freezing point of ice to well below zero. The 12-year-old Pittsburgh boy suffered second-degree frostbite-like injuries.

Fire challenge

This involves dousing yourself in flammable liquid and setting it on fire. Some teens feel reassured in taking the challenge when others online appear relatively unscathed. They may not realize the stunt can also end in disaster. Last summer, a 15-year-old boy in Buffalo, N.Y., died after taking part in the challenge.

Smoking alcohol

Depictions of vaporizing and inhaling gaseous alcohol have gained popularity on YouTube in recent years. The practice has been touted as a way to reduce the number of calories you take in during a night of partying. It's dangerous because the vapours bypass the liver and go straight to the lungs and brain, and there's a far greater risk of getting alcohol poisoning.

The Kylie Jenner lip challenge

Blame the Kardashian-Jenner clan and the selfie craze for this trend, recorded on Instagram and Twitter in recent weeks. This entails sticking a shot glass over the lips and then sucking out the air, creating a partial vacuum. Yes, lips will look plumper for an hour or two, but many teens who take the challenge are left with bruising around the mouth that lasts a lot longer. Some doctors warn the challenge can even lead to permanent damage. Reality TV personality Kylie Jenner has told her 8.4 million followers on Twitter that she does not encourage this kind of poofing.

The thigh gap

Thigh gap

The so-called thigh gap trend among teenage girls was cited when Target admitted last year that it went too far with Photoshop in an online ad for this bathing suit. (workthatmatters.blogspot.ca)

Social media sites have been fuelling this potentially risky body image trend. The fashion industry adds to it, with models showing space between their upper legs, even when they're pressed together. Since it's a look that is nearly impossible for most people to achieve, critics say it can lead to extreme dieting.

Sexting

Ontario's new sex-ed curriculum will include a look at the risk of sexting. "Once a person sends a sext, they lose control of it," the update's guide to the curriculum says.

Grizzly selfies

Last October, the U.S. Forest Service issued a plea to tourists to leave the bears alone. Wildlife officials singled out visitors to South Lake Tahoe in California after snapshots of young people posing with grizzly bears in the background surfaced on Instagram and Twitter.

Car surfing

So-called car surfing is a dangerous stunt that involves trying to balance on top or on the back of a moving car. (YouTube)

Car surfing

A spate of car-surfing accidents in Canada occurred several years ago, suggesting copy cats were inspired by what they saw on social media.

Instagram drug sales

More and more these days, it seems illegal drugs are being sold through photo-oriented Instagram. The service has been known to block certain hashtags to discourage drug dealing, but has not been able to keep up with the trend. Sellers often change their hashtags daily.