An idle facebook discussion, wherein I discuss eating thousands of liters of toothpaste.

A Facebook friend posted a meme discussing the dangers of fluoride toothpaste, so I did a little math:

“It takes 5-10 grams of sodium fluoride to kill a full grown human. Fluoride drinking water contains less than a single part per million. (about 0.5 ppm, usually.) The average person consumes a bit more than a swimming pool worth of water in their lifetime. (Around 87,000 liters). The amount of fluoridated water that would be required to reach 5 grams of sodium fluoride? 10 million liters. Humans are literally incapable of drinking enough fluoridated water to kill themselves, or even enough to cause tooth color mottling, the first effect of fluoride buildup to appear. (Other fluoride salts than sodium fluoride can be used, but similar math applies.)
What about toothpaste, though? Well, sodium fluoride in toothpaste (or in fluoridated water) reacts with apatite (the mineral your teeth are made of- I’m fairly sure the pun was intended) to to form fluorapatite, which occurs naturally in enamel. (There’s a lot of fluoride on Earth- as the lowest atomic weight halogen, there’s a ton of it around.) The levels of fluoride in toothpaste are pretty carefully calculated so that most of it is used in the reaction that forms fluorapatite, and the rest gets spat out. In order to actually get fluoride poisoning from toothpaste, which has around 1,000 ppm of fluoride, you’d have to eat several thousand liters of toothpaste. Again, rather impractical. You’ll never put enough toothpaste in your mouth to cause even the most minor of symptoms, even if you retained 100% of the fluoride (which your body slowly flushes out over time) and none of it reacts with the apatite in your teeth.
Fluoride poisoning does occur, but not from toothpaste or fluoridated drinking water. More often, it’s from industrial waste or wells built in regions with certain types of high-fluoride granite.”
Moral of the story? Don’t eat thousands of liters of toothpaste.