If you have ever taken a good look at the back of a tube of toothpaste during those long two minutes of recommended brushing time, you may have noticed sodium laureth sulfate (SLES) and sodium lauryl sulfate (SLS) listed as ingredients. Both of these are usually listed as a duo and are responsible for that bitter yucky taste that comes about when biting an orange after tooth brushing. Oranges contain a fair bit of citric acid, which has both a bitter and sour taste. For some reason, these compounds enhance the bitter taste and leaves the sour taste unaffected. Interestingly enough, this does not happen to everybody. It seems that a genetic predisposition is required.
Widely found in cleaning agents ranging from shampoos to dishwashing products, these substances are synthetic detergents (or “syndets”), and were originally developed by chemists to eliminate scum formation, a problem commonly found when cleaning with soap. Unlike syndets, soaps react with dissolved minerals in water to form an insoluble precipitate, often seen as the scummy bathtub ring. Syndets are long molecules, one end of which dissolves in fat and the other in water. In this way, it forms a link between fatty deposits and water, allowing the fat to be emulsified and rinsed away. Bye-bye soapy bathtub ring!
But (surprise, surprise!), like all chemical compounds found in our food and/or everyday products, both SES and SLS have come under scrutiny. Scientific ignorance is at least partially responsible. There is much discussion on these websites about SLS and SLES being contaminated with carcinogenic nitrosamines. While it is true that trace amounts of nitrosamines have been found in some shampoos, they have nothing to do with sodium lauryl or laureth sulfate, but rather “ethanolamine lauryl sulfates”, a compound that yes, has been found to form nitrosamines. To the lay person, all these compounds may sound similar, but it is important to note that they are not.
This is also the root cause for the dioxin/dioxane panic when it comes to SLS. Dioxin is carcinogenic. Dioxane, on the other hand, is not. And it is the latter that is used as a solvent in SLS manufacturing, meaning it could remain in trace amounts. But it is not hazardous, let alone cancerous.
And that is the full story behind why your orange tastes bitter after brushing your teeth.
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