What Happens When Chemists Don't Wash Their Hands

Three different artificial sweeteners have been the result of scientists with poor hand hygiene.

Serendipitous discoveries tend to happen in unexpected ways. But the stories of the serendipitous discoveries of three different artificial sweeteners are, in their basic components, identical. All three were discovered when a scientist put his hand to his mouth and tasted something unusually sweet.
Saccharin, 1897, Johns Hopkins University
One night, Constantine Fahlberg came home from the lab, picked up a piece of bread, and took a bite. It was sweet—much sweeter than sugar—and he realized he was eating bread dusted with some chemical he'd made that day at work.
"The only way to find out what was sweet on his lab bench was to literally taste everything," Michal Meyer, the editor-in-chief of Chemical Heritage, explains in this video. So he did, and he found that a compound called benzoic sulfimide was responsible. He called it saccharine; and to find out if it was safe, Meyer says, he "took 10 grams...swallowed it, waited for 24 hours to see what would happen and found it went right through him. It was basically unmetabolized by his body."
He decided it was safe. Since then, it's been used in all kinds of drinks, particularly during World War II when sugar supplies were low. Today, you can enjoy saccharin in the little paper packets of Sweet n’ Low.
Cyclamate, 1937, University of Illinois
Michael Sveda was working on his doctorate and had recently started smoking cigarettes. (He had previously preferred smoking pipe tobacco, but the local supply had been ruined by a flood.) One day in the lab, he reached up to brush a piece of tobacco off his lips and tasted something sweet. Like Fahlberg, he decided the way to figure out what it was, was to taste every beaker he'd been working with until he found the one that was sweet. That was cyclamate. But unlike Fahlberg's saccharine, you can't stir any cyclamate into your coffee today. The FDA would ban its use in 1969 after it caused cancer in rats.
Aspartame, 1965, G.D. Searle & Co.
James Schlatter was trying to create a compound to treat gastric ulcers. He was in the lab, he later said, when...

...licking my finger to pick up a piece of paper, I noticed a very strong, sweet taste. Initially, I thought that I must have still had some sugar on my hands from earlier in the day. However, I quickly realized this could not be so, since I had washed my hands in the meantime. I therefore, traced the powder on my hands back to the container into which I had placed the crystallized aspartyl-phenylalanine methyl ester.

He felt, he said, that the tester was "not likely to be toxic and I therefore tasted a little of it and found that it was the substance which I had previously tasted on my finger."
Aspartame is, like saccharine, still widely used to sweeten beverages. You drink it every time you rip into a packet of NutraSweet or Equal, and it sweetens many soft drinks. The FDA has evaluated the sweetener a handful of times, and despite what the Internet might tell you, it's perfectly safe—far safer than tasting every chemical in your lab.