Thanks for setting me straight, Fred. I can't cite the name of the study and don't have time now to look it up, but I recall reading an SLS toxicology report using the rabbit ear assay that showed precancerous changes in the skin. Somewhere I also got the idea that SLS was used in laboratory settings as an irritant. I see now that more recent toxicology reports have found no evidence for carcinogenicity. I was wrong!

However, it's important to realize that these reports address the safety of SLS only in isolation of other chemicals. In a real-world setting, SLS is used in combination with many other ingredients that may combine to form, e.g., nitrosamines, which have a more credible (but not conclusive) cancer link. And regardless of its carcinogenicity, it has been shown to gather in brain and liver tissue, as well as cause damage to developing cornea. But the only relevant consideration is whether enough of it gathers in enough tissue over a lifetime to disrupt normal biological processes. I think we can pretty safely say that SLS is not going to hurt anyone who shampoos on an ordinary basis. Just as we can say that bisphenol-A probably won't hurt those of us who drink bottled water, but what about the guy who microwaves his dinner in tupperware every night and only eats canned goods? Is that comparable to the guy who leaves glue in contact with his scalp for weeks at a time?

Finally, its carcinogenicity is independent of the point I was trying to make, which is that our environment is filled with all sorts of mini risks and dangers, some of which are worth getting worked up over and some of which are just a wate of time.

All this typing has made me hungry. I think I'll go eat a non-organic apple.