A 12-year-old US boy has suffered second-degree burns after taking part in an internet craze called the "salt-and-ice challenge".
The boy, from Pittsburgh, had the shape of a large cross burnt into his back by his twin brother and a friend after a dare.
The children applied salt onto the skin and then ice cubes on top of it, causing frostbite-like burns, the NY Daily News reports.
The boy's mother, who requested that she and her son remain unidentified, said she initially yelled at her son when she saw what had happened.
She said her son had lost all sensation in the affected area during the 20-minute challenge.
But the next day the burn began to blister and she took him to the emergency room, where doctors said the injury could lead to scarring.
The "salt-and-ice challenge" has become a growing phenomenon after several videos were posted on YouTube showing people inflicting similar burns.
"The injury is similar to frostbite that can result in mild cold injury but it also could increase in severity based on the time the ice is applied," Dr. Ariel Aballay, director of the West Penn Hospital Burn Center, said on Friday.
"This patient went for a few minutes, but there have been cases that went for six or seven minutes that resulted in third-degree injuries."