 Sodium laurel sulfate is a common detergent used in toothpaste. It was featured in famous internet hoax nearly 20 years ago. Colgate toothpaste has it, supposedly proven to cause cancer. At least by buying Colgate rather than Cresce, you wouldn't be supporting Satan, or so claimed another famous hoax. The hoax that sodium laurel sulfate in toothpaste and hair care products was linked to cancer became so widespread, the American Cancer Society was forced to publish a response to shampoo the link. Radical emails have been flying through cyberspace, stating sodium laurel sulfate causes cancer, and it's simply not true. So I just ignored it all these years until I was doing research on canker sores. You know those painful shallow gray ulcerations you get inside your lip or cheek, also known as aphid ulcers. They can often be set off by trauma, like if you accidentally stab yourself with a toothbrush or something. And so they recommend to try to avoid biting your lip, and also to avoid sodium laurel sulfate containing toothpaste, not because of cancer, but apparently for irritation, which at least makes a little more sense. I mean, why would a detergent, a soap chemical, be carcinogenic? Though you could imagine how it might theoretically at least dissolve off some protective layer from the inside of your mouth or something, so I decided to look into it. Although SLS has been used as a foaming agent in toothpaste since the 1930s, our story begins 25 years ago, with an abstract presented at a conference on the possible effects of sodium laurel sulfate on recurring canker sores. They took 10 men and women getting more than one sore a week, nearly 18 on average over a three-month period, using a regular SLS-containing toothpaste, and then they switched them to using an SLS-free toothpaste for another three months. And they went from 18 canker sores down to around five. That's like a 70% decrease. And indeed, what they thought was happening is that the sodium laurel sulfate was adversely affecting the protective mucus layer that lines our mouth. You always have to be cautious about published abstracts, though you always want to make sure that they actually go on to publish their findings in a peer-reviewed medical journal. And indeed, in this case, they did. So you can confirm that yes, indeed it was a double-blind study. Yes, indeed they used the exact same toothpaste, just one with the regular concentration of SLS and the other SLS-free. But still, just 10 patients? It was considered a preliminary study with apparently such a dramatic effect. A series of experiments were performed to see what might be going on. As simple as just applying some SLS at the concentration found in toothpaste onto someone's gums with a Q-tip for 90 seconds and measuring the spike in blood flow to the area, which is a sign of inflammation, presumably because the detergent was penetrating and irritating the gums. Yeah, but does it actually damage the tissue? Researchers smeared some toothpaste on the gums of some dental hygienists. Two minutes twice a day for four days. And while the SLS-free toothpaste didn't cause any problems, the ones with the typical amount of sodium lauryl sulfate caused desquamation among most of them. In other words, a sloughing off or peeling of the topmost layers of the inside lining of their mouths. No wonder it might make canker sores worse. It's funny if you go back to the original American Cancer Society debunking, their response was sodium lauryl sulfate is not a known carcinogen. It's just a known irritant.