When Mae Keane died at the age of 107 in March 2014, reports of her death focused not on her extraordinarily long life, but on the fact she probably should have died nearly nine decades earlier, of radiation poisoning.   It’s believed that Keane was the last of the so-called Radium Girls -- a group of several thousand young female factory workers in the early 20th century who for years worked with one of the world’s most radioactive substances -- and suffered the consequences.   Nearly a century later, their story is a reminder that it can take us a while to fully grasp the downsides and side effects of new discoveries.   And at the turn of the 20th century, radioactive elements were far from being fully understood.   Radium was discovered in 1898 by Marie and Pierre Curie. They were interested in the fact that minerals containing the element uranium gave off electromagnetic radiation that could pass through metal.   Marie Curie investigated these rays, focusing on the mineral pitchblende, where uranium is often found. She discovered the mineral gave off more radioactivity than could be accounted for by uranium alone.   Together, she and her husband succeeded in isolating both element 84, dubbed polonium and element 88 -- radium -- in the pitchblende.   The spontaneous release of energy from rocks was as exciting as it was perplexing -- it was considered to be a new force of nature. But little was known about radium’s properties or dangers.   It didn’t take long for doctors to find that the application of radium salts to a cancerous tumor would often shrink the tumor.    If it’s good for shrinking tumors, must be good for everything, right?   So, by the early 1900s, “radium therapy” gave birth to an entire industry of phony cure-all medicines and elixirs.   Everything from radium soda to radium toothpaste soon appeared on shelves. Even radium water was a thing.    Luckily for consumers, most of these products contained such low levels of radium that they were pretty much harmless.   But then someone discovered how to turn radium into glow-in-the-dark paint.   Radium itself doesn’t actually glow, but Marie Curie famously described the blue “fairy-like” color she saw while working with the mineral.   The effect is caused by the interaction of radium with other chemicals as it decays.    As it decays, radium releases particles that ionize nearby materials, creating positively charged ions that pull negatively-charged electrons from other nearby atoms.    The glow occurs when the electrons return to their original state, releasing that extra energy as light.   In 1902, an inventor named William Hammer -- who would be the first person to suggest using radium as a cancer treatment -- used samples of radium salt given to him by the Curies and mixed it with glue and zinc sulfide to create a luminescent paint.   Hammer found a variety of uses for this new luminous material -- which he called Undark -- from toys to gun sights. But the the most popular was for the dials on watches and clocks, so they could be seen in the dark.    By the early 1920s, Undark was being used by the U.S. Radium Corporation in New Jersey, where more than 4,000 workers -- mostly young women -- used it to paint tiny, glowing numbers on watch faces.   Even though the company’s own chemists made sure to handle radium behind lead shields, the radium painters weren’t given much in the way of protection.    In fact, workers were encouraged to use their lips and tongues to shape the tips of their brushes.   Soon, the effects of the radium showed up in the health of the workers.    Even though very high, but very localized, exposure to radium can kill cancer cells in some cases, ingesting large amounts of it over time exposes the whole body to its damaging effects.   And what makes radium particularly dangerous when it’s ingested is that it has chemical properties similar to calcium, so it’s easily absorbed into bones, teeth, and other tissues.    As a result, the women soon developed tumors, bone-marrow damage and leukemia.   Other workers started losing teeth, suffering from deteriorating jawbones, mouth cancers, sores and anemia.    By the late 1920s, the health concerns about radium started to become public.    And in 1927, five of the painters sued their employer for damages and medical expenses, and won. But by then, dozens of past and present radium painters had died.   That Mae Keane survived is probably due to the fact she found the paint gritty and didn’t like the feel of it in her mouth.   To this day, if you run a Geiger counter over the graves of many of the women who died nearly 90 years ago, the needle will jump.    Near a century after they introduced the world to the dangers of radium first-hand, the radium girls remain radioactive.   Thanks for watching this SciShow Dose, brought to you in large part by today’s President of Space, Soliloquy. You can check out his Youtube channel by following the link in the description. If you would like to become a President of Space, or just support SciShow and receive monthly rewards, go to Patreon.com/SciShow