The idea of Scratch and Sniff has been around since the 1970s. Scientists developed a method of "trapping" scent in a process called "micro-encapsulation". They inserted the fragrance in tiny plastic or gelatin spheres which, when you rubbed or scratched them, would break open, emitting the trapped scent. The idea became popular in children's books and stickers.
Some stickers came free in boxes of cereal or attached to the covers of magazines. Others were sold in multipacks, perhaps depicting a cartoon character.
The problem was that the scent capsules could be applied only to stickers or book pages made from fairly thick paper or card. Although they are almost microscopic, they were too heavy to be applied to newspapers. But Hong Kong professor of micro-inkography and Sniffit's CEO, Chi Ting-man, has been working on fixing that problem.
"I remember my sisters used to get really excited when they got a sticker on the front of a comic. They'd squeal with delight as they rubbed the fruit-shaped freebie, and smelled strawberries, lemons or, even better, their favourite candy," Chi said. "I wanted to bring that nostalgic feeling to Hong Kong students today. Young Post is the perfect vehicle for this."
Scratch and Sniffs of the past required an extra layer to be added to the printing process. But Chi has managed to design even tinier micro-capsules of scent that can be mixed with ordinary newspaper ink. When the ink is scratched, the scent emerges, just like on the old stickers.
"Individual beads of oil carry the scent," he said. "Modern nano-technology has allowed us to do this. I've called it 'Smellink'."
Dr Ayam Lai Ying-tu, of the Institute of Advanced Assorted Scent Sciences on the mainland, helped Chi with his studies. "It's bringing a whole new element to print journalism," he said.
YP editor Susan Ramsay decided to bring the scents alive on the paper's cover with an image of boy band This Just In.
"The guys like different kinds of cologne," she explained. "Kevin is into sporty fragrances, so we've printed him with a fresh, citrusy ink.
"Hei likes woody, musky notes, so we've gone for a classic aftershave smell for him. Chris likes complex colognes, so if you scratch his image it smells like a blend of pine, bergamot and cedar. Leon likes light, oceanic smells that remind you of beach holidays.
"We also used Smellink to print Chris' hat in a leather-scented ink," Ramsay added. "The red flower in the masthead smells of raspberry, and the pink one of marshmallows."
Young Post, the editor said, is "always trying to find new ways to make reading our stories even more enjoyable".