10 Incredible Things That Were Invented By Accident

A mix of human error and pure coincidence has led to some amazing inventions.
This simple cereal has a particularly intriguing backstory.
This simple cereal has a particularly intriguing backstory. / Image Source/Stockbyte/Getty Images

Not every great invention was created according to plan. Some, in fact, were the result of a happy accident. In November 2020, for example, the pharmaceutical company AstraZeneca announced that the COVID-19 vaccine it had developed in partnership with Oxford University was 90 percent effective when administered in a dosing regimen they had discovered thanks to some “serendipity.” This wasn't the only unintentional discovery in history, of course. From penicillin to artificial sweeteners, all 10 of the everyday items below were invented entirely by accident.

1. Penicillin

A black and white photograph of a Petri dish of penicillin
A Petri dish of penicillin, 1954. / Keystone Features/GettyImages

On September 28, 1928, Scottish scientist Alexander Fleming discovered that a Petri dish of Staphylococcus bacteria that had been inadvertently left out on the windowsill of his London laboratory had become contaminated by a greenish-colored mold—and encircling the mold was a halo of inhibited bacterial growth. After taking a sample and developing a culture, Fleming discovered the mold was a member of the Penicillium genus, and the rest, as they say, is history.

2. Corn Flakes

Corn Flakes cereal boxes, 1950.
Corn Flakes cereal boxes, 1950. / Steven Gottlieb/GettyImages

The two Kellogg brothers—Dr. John Harvey Kellogg and his younger brother (and former broom salesman) Will Keith Kellogg—worked at Battle Creek Sanitarium in Michigan, where John was physician-in-chief. Both were strict Seventh-Day Adventists, who used their work at the sanitarium to promote the austere dietary and moralist principles of their religion (including strict vegetarianism and a lifelong restraint from excessive sex and alcohol). They also carried out research into nutrition and the impact of diet on their patients. It was during one of these experiments in 1894 that, while in the process of making dough from boiled wheat, one of the Kelloggs left the mash to dry for too long. When it came time to be rolled out, the mixture splintered into dozens of individual flakes. Curious as to what these flakes tasted like, he baked them in the oven—and in the process, produced a cereal called Granose. Some later tinkering switched out the wheat for corn and gave us corn flakes.

3. Teflon

Polytetrafluoroethylene—better known as PTFE, or Teflon—was invented by accident at a DuPont laboratory in New Jersey in 1938. Roy Plunkett, an Ohio-born chemist, was attempting to make a new CFC refrigerant when he noticed that a canister of tetrafluoroethylene, despite appearing to be empty, weighed as much as if it were full. Cutting the canister open with a saw, Plunkett found that the gas had reacted with the iron in the canister’s shell and had coated its insides with polymerized polytetrafluoroethylene—a waxy, water-repellent, non-stick substance. DuPont soon saw the potential of Plunkett’s discovery and began mass-producing PTFE, but it wasn’t until 1954, when the wife of French engineer Marc Grégoire asked her husband to use the same substance to coat her cookware to stop food sticking to her pans, that the true usefulness of Plunkett’s discovery was finally realized.

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4. The Slinky

A Slinky, Magic 8 ball and Plasma Ball displayed on a shelf
The Slinky has kept countless kids entertained since its accidental invention. / Rodin Eckenroth/GettyImages

In 1943, naval engineer Richard T. James was working at a shipyard in Philadelphia when he accidentally knocked a spring, which he had been trying to modify into a stabilizer for sensitive maritime equipment, from a high shelf. To his surprise, the spring neatly uncoiled itself and stepped its way down from the shelf and onto a pile of books, and from there onto a tabletop, and then onto the floor. After two years of development, the first batch of 400 “Slinky” toys sold out in just 90 minutes when they were demonstrated in the toy department of a local Gimbels store in 1945.

5. Silly Putty

At the height of World War II, rubber was rationed across the United States after Japan invaded a number of rubber-producing countries across Southeast Asia and hampered production. The race was on to find a suitable replacement—a synthetic rubber that could be produced in the U.S. without the need of overseas imports, which eventually led to the entirely unexpected invention of Silly Putty.

There are at least two rival claims to the invention of Silly Putty (chiefly from chemist Earl L. Warrick and Scottish-born engineer James Wright), both of whom found that mixing boric acid with silicone oil produced a stretchy, bouncy, rubber-like substance that also had the unusual ability of leaching newspaper print from a page (an ability that new printing technology has now eliminated).

6. Post-It Notes

Post-It notes on a wall after an exercise during the SheChampions Summit, 2023.
Post-It notes on a wall after an exercise during the SheChampions Summit, 2023. / ISI Photos/ISI Photos/GettyImages

In 1968, a 3M chemist named Dr. Spencer Silver was attempting to create a super-strong adhesive when, instead, he accidentally invented a super-weak adhesive, which could be used to only temporarily stick things together. The seemingly limited application of Silver’s product meant it sat unused at 3M (then technically known as Minnesota Mining & Manufacturing) for another five years, until, in 1973, a colleague named Art Fry attended one of Silver’s seminars and struck upon the idea that his impermanent glue could be used to stick bookmarks into the pages of his hymnbook. It took another few years for 3M to be convinced of Fry and Silver’s idea and its salability, but eventually the inventors came up with a unique design that worked perfectly: a thin film of Spencer’s adhesive was applied along just one edge of a piece of paper. After a failed test-market push in 1977 as Press ’N Peel, the product went national as the Post-It note in 1980.

7. Saccharin

In 1878 or '79 (sources differ), Constantin Fahlberg, a chemistry student studying Professor Ira Remsen at Johns Hopkins University in Baltimore, Maryland, discovered while eating his meal one evening that food he picked up with this fingers tasted sweeter than normal. He traced the sweetening effect back to the chemical he had been working with that day: ortho-sulfobenzoic acid imide. Thinking he could be on to something, he quickly set up a business mass-producing his sweetener under the more pronounceable name saccharin. Although saccharin was popular with consumers, it would take the sugar shortages of two World Wars to make the discovery truly ubiquitous.

8. Popsicles

photo of someone holding a pink, fruity popsicle outside
A kid accidentally invented the first of these sweet treats. / Noam Galai/GettyImages

The first popsicle was reportedly invented by 11-year-old Frank Epperson in 1905, when he accidentally left a container of powdered soda and water, with its mixing stick still inside, on his porch overnight. One unexpectedly cold night later, the popsicle—which Epperson originally marketed 20 years later as an Epsicle—was born.

9. Safety Glass

The process of making safety-glass windshields
The process of making safety-glass windshields. / Avalon/GettyImages

Safety glass—or rather, laminated glass—was accidentally discovered by the French chemist Édouard Bénédictus when he knocked a glass beaker from a high shelf in his laboratory and found, to his surprise, that it shattered but did not break. His assistant informed him that the beaker had contained cellulose nitrate, a type of clear natural plastic, that had left a film on the inside of the glass. He filed a patent for his discovery in 1909, and it has been in production (albeit in various different forms) ever since.

10. Smoke Detectors

A smoke detector and sprinkler installed in a dropped ceiling.
A smoke detector and sprinkler installed in a dropped ceiling. / Michael Jacobs/Art in All of Us/GettyImages

Next time your smoke detector goes off in the middle of the night, thank Walter Jaeger. The Swiss physicist was trying to create a something that could detect poison gas in the 1930s. But instead of alerting him to the presence of gas, his detector instead picked up on the smoke from his cigarette.

A version of this story originally ran in 2016; it has been updated for 2024.