How do scratch-and-sniff stickers work?

Scratch-and-sniff stickers are novelties that delight both children and adults. Sniff out the ingenious technology that makes them work in this podcast from HowStuffWorks.com.

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Episode Transcript

Speaker 1 (00:00):
Welcome to brain stuff front house, stuff works dot Com
where smart happens. Hi Am Marshall Brain with today's question,
how do scratch and sniff stickers work? Scratch and sniff
stickers are one of those novelty technologies that sound like

(00:23):
such a great idea, but they've never really caught on
except in children's books and the occasional perfume strip in
a magazine. But if you do have kids, you probably
have a scratching sniff book around the house, and even
if the book is twenty years old, it still works.
The reason the stickers last so long is because of
the micro encapsulation technology used to create them. The basic

(00:47):
idea behind scratch and sniff is to take the aroma
generating chemical and encapsulate it in a gelatin or plastic sphere,
and these spheres are incredibly small, on the order of
a few microns in diameter. When you scratch the sticker,
you rupture some of these spheres and release the smell.
The smell is essentially held in millions of tiny bottles,

(01:12):
and you break a few of those bottles every time
you scratch the sticker. The tiny bottles preserve the fragrance
for years. It turns out that the micro encapsulation technology
used in scratch and sniff was first developed to create
carbon less copy paper. The top sheet of the paper
is coated with the micro capsules containing a colorless ink.

(01:34):
When you write on the paper, it breaks the capsules
and releases that inc The ink mixes with a developer
chemical on the next sheet of paper, and it creates
a dark color. It's carbon less carbon papers. For more
on this and thousands of other topics, is it hastaff
works dot com.