when were stickers invented

Short answer: adhesive labels showed up in the 19th century—postage stamps in 1840 used lick-and-stick gum, and shopkeepers used gummed labels in the late 1800s.

The modern peel-and-stick sticker arrived in 1935 when R. Stanton Avery created pressure‑sensitive labels with a backing paper.

Bumper stickers went mainstream in the 1940s, riding the post‑war road‑trip boom and cheap screen printing.

So: proto‑stickers in the 1800s, proper self‑adhesive in 1935, then a worldwide outbreak of sticky opinions after WWII—still clinging to lunchboxes everywhere.