If you use shampoo to wash your hair, it probably works up into a nice, thick lather. This thick lather, for many of us, really defines the shampooing experience. Imagine, then, discovering that this lather could kill you.
In 1998, an email first made the internet rounds that instilled fear in shampoo users around the globe. The email, anonymous of course, claimed that shampoo could be causing cancer. The culprit, according to the email, was sodium laureth sulfate, also known as SLES. This is the ingredient in shampoo that creates lather. Today, a quick search for "does shampoo cause cancer" still brings up a host of dodgy-looking websites with questionable "data" sources, claiming the same ingredient, along with more than a dozen others, is carcinogenic.
In fact, the more common lather-producing agent is sodium lauryl sulfate, SLES's less-expensive cousin. The molecules are very similar, though.
Sodium lauryl sulfate (SLS) is a detergent, a crystalline salt of sulfated lauryl alcohol. It's good at general cleaning because it's a surfactant — a substance that breaks up surface tension, the bonds between molecules in the outer layer of a compound. This is how SLS produces lather. It eases those bonds, allowing two separate entities — say, shampoo and your hair — to interact more effectively. Without this loosening of surface bonds, shampoo wouldn't be as good at removing dirt and oil from your hair.
SLS is a common ingredient in all sorts of cleaning products. You'll also find it in toothpastes, mouthwashes, hand creams, sunscreens and, as noted with horror in the anonymous email, garage-floor cleaners.
The most common reaction at this point is: Really? The stuff in our shampoo is also in garage-floor cleaners? How can that be safe?
It's a bold claim, and the email had the desired effect. Lots of people switched to "all-natural" shampoos that proudly assert their SLS-free status, presumably to avoid shampoo-related cancer risk. But are these people really less likely to develop cancer than those of us who use regular old SLS-containing shampoo?
As it turns out, there are certain risks associated with sodium lauryl sulfate, but not the one you're thinking of.