20 Times a Scientific Mistake Led to a Major Discovery

In 1928, Alexander Fleming left a Petri dish containing staphylococcal bacteria out in the open before going on vacation; when he returned, mold had contaminated the dish and destroyed everything in it. It was Penicillium notatum, and that is how the era of antibiotics began—simply because a scientist had forgotten to put things away before going on vacation.

In 1895, Wilhelm Röntgen noticed that a fluorescent screen at the other end of the room was glowing, even though his cathode-ray apparatus was completely shielded. What was passing through the shielding turned out to be electromagnetic radiation that would go on to become one of medicine’s most essential diagnostic tools.

Henri Becquerel had left some uranium salts on a photographic plate in a drawer after cloudy weather had thwarted the experiment he had planned to conduct in sunlight; when he developed the plate anyway, he discovered a very clear image that the uranium had produced on its own. It was because the weather wasn’t cooperating that the study of radioactivity began.

In 1839, Charles Goodyear poured a mixture of rubber and sulfur onto a hot stove and found that the result was strong, flexible, and heat-resistant—unlike natural rubber. He had been trying to achieve this result for years, and the answer came to him by chance, on a hot stove.

In 1945, while working at Raytheon, Percy Spencer noticed that a chocolate bar in his pocket had melted while he was standing near a running magnetron. Far from being annoyed by this, he began experimenting with other foods. Within a few years, that melted chocolate bar would become one of the most common household appliances in the world.

In 1938, while working at DuPont, Roy Plunkett opened a container that appeared to be empty and discovered that tetrafluoroethylene had polymerized into a waxy solid that he had not set out to create. This solid became Teflon, which is found everywhere today, from spacecraft to nonstick pans.

In 1879, Constantin Fahlberg sat down to eat without washing his hands after handling coal tar derivatives, and he noticed that everything he touched tasted unusually sweet. He returned to the lab that same evening to identify the compound responsible, and that is how he discovered saccharin, the first artificial sweetener.

In the late 18th century, Humphry Davy suggested that nitrous oxide might be useful in surgery, as it appeared to eliminate pain, but this observation was ignored for decades, while the gas became a popular form of entertainment at parties. Horace Wells attended one of these demonstrations in 1844, saw someone injure themselves without feeling any pain, and ultimately paved the way for the introduction of anesthesia into clinical practice.

In 1943, Albert Hofmann accidentally ingested a tiny amount of a lysergic acid compound at Sandoz Laboratories, and the effects he experienced on his bike ride home prompted him to begin deliberate research the very next day. LSD has become a major tool in psychiatric research and is currently experiencing a significant resurgence of clinical interest in the treatment of depression and addiction.

In 1964, Arno Penzias and Robert Wilson spent months trying to eliminate a persistent hissing sound coming from an antenna at Bell Labs, even going so far as to chase the pigeons off the dish, before realizing that the noise was not coming from the equipment. It was, in fact, the thermal afterglow of the Big Bang, and it was this unsuccessful troubleshooting effort that earned them the Nobel Prize in Physics.

In the 1920s, in the northern United States, cattle were dying from uncontrollable bleeding caused by eating fermented sweet clover hay, and Karl Link’s team spent years isolating the compound responsible. The synthetic version of this compound became warfarin, one of the most widely prescribed anticoagulants in history.

Iproniazid was an anti-tuberculosis drug that seemed to make patients exceptionally cheerful and energetic, even when the disease itself was not improving. This observation made it one of the first antidepressants and led to the development of the entire class of monoamine oxidase inhibitors.

Minoxidil was developed in the 1960s as an oral medication for high blood pressure, and patients consistently reported that their hair was growing back in areas where it had stopped growing. This cardiovascular medication found a new purpose as a topical treatment for hair loss and has been marketed under the brand name Rogaine since 1988.

In the late 1980s, Pfizer studied sildenafil as a treatment for angina and found that it was not particularly effective; however, the male participants were particularly reluctant to return their unused pills. The researchers investigated this further, and that is how Viagra was born out of a cardiovascular trial that had ended in failure.

During World War II, James Wright developed an elastic, stretchy compound at General Electric while attempting to create synthetic rubber, but the product proved unusable for that purpose. It lay unused for years until a marketing specialist, Peter Hodgson, packaged it in plastic eggs and turned it into one of the most iconic toys of the century.

In 1903, Édouard Bénédictus dropped a glass vial in his Paris laboratory and noticed that it retained its shape instead of shattering, because a solution of cellulose nitrate had dried and coated the inside. He later made the connection between this memory and reports of injuries caused by windshields in car accidents, and it was from that simple dropped bottle that he developed laminated safety glass.

During his experiments on electric fields in the 1960s, Barnett Rosenberg noticed that the bacteria had stopped dividing; he initially attributed this phenomenon to the electric current, when in fact it was caused by a platinum compound dissolving on his electrodes. Correcting this misinterpretation directly led to the discovery of cisplatin, which remains one of the most important chemotherapy drugs today.

In 1941, George de Mestral returned from a hike covered in burdock seeds; after examining one under a microscope, he discovered tiny hooks that clung to the loops in fabric and fur. He spent years developing an artificial version of this mechanism, and ever since, Velcro has been used to fasten objects together.

Chlorpromazine was an antihistamine used preoperatively until surgeon Henri Laborit noticed that patients given the drug exhibited an unusual indifference to their surroundings and suggested trying it in psychiatry. Tested on patients with severe psychosis in Paris in 1952, it became the first effective antipsychotic drug and revolutionized psychiatric care.

In 1956, while building a heart sound recorder, Wilson Greatbatch used the wrong resistor, causing the circuit to produce a rhythmic electrical pulse instead of recording anything. He noticed that this pattern resembled the human heartbeat and spent the next two years turning this assembly error into an implantable pacemaker.