An Auckland skin expert says young people taking part in the "frosty challenge" risk being scarred for life.

Young people taking part in the frosty challenge spray aerosol to the skin at close range for as long as possible, and compete with each other to see who can endure it the longest.

Auckland Skin and Cancer Foundation consultant Chin-Yun Lin described the challenge as a "silly craze", adding the use of any aerosol products in close proximity to the skin for a prolonged period can lead to permanent damage or disfigurement.

"There's a risk of ice burn, which is very similar to heat burn, and the longer you spray, the deeper the skin will freeze and the deeper the wound," Lin said.

"When you reach an equivalent to a third-degree burn, which goes through the dermis and affect deeper tissues, that would lead to permanent scarring and quite a lot of disfiguration."

Lin said the frosty challenge was a "stupid practice" that should "definitely not be encouraged".

Many who take part in the so-called challenge are filming themselves and posting the footage on YouTube and other social media channels.

Fashion blogger Leonie Barlow yesterday posted a photo of her son's deep wound on his leg, which hasn't healed even after two weeks.

She wrote: "This is what happens when your 13-year-old son accepts a stupid dare at school!"

Barlow said her son sprayed a deodorant can a few centimetres above the skin and lasted about 30 seconds.

"A few other of his friends also did it, but their injuries are not that bad," she said.

"He obviously did it for the longest, and the reward for being the best at that is this deep, deep burn in your leg."

It was done after school hours so none of his teachers knew about it.

"He has been hiding it from everyone because he feels like an absolute fool," Barlow said.

"The chemical burn is a very deep burn, so what looks like something that is fairly harmless to do, when sprayed on a concentrated area of skin over a period of time is going to burn really deep."

Barlow said she posted the image because she wanted to warn others about the dangerous prank.

She wants parents to show their kids the photo, and tell them "how stupid it is to get a frosty".