I'm a medical doctor, board-certified in both anatomic and clinical pathology. I operate the world's largest free online personalized health information service.
Before posting this note, I had gotten at least twenty inquiries about the sodium lauryl sulfate E-mail campaign. The author claims that sodium lauryl sulfate, a detergent found in some shampoos and toothpastes, causes cancer in laboratory studies using animals.
The E-mail itself was fake [best link is now down]. The author was listed as a member of the U. Penn. medical community. A phone call to the number listed on the E-mail indicated that no one there had anything to do with it.
Lauryl sulfate is made by joining sulfate and lauric acid, two substances which are both abundant throughout the body in health. It is a good solubilizing agent and is also used in acrylamide gel electrophoresis. "Laureth" indicates ethoxylation ("lauryl" on one side of the sulfate group, an ethyl ether on another).
Life has taught me not to attribute to malice what is adequately explained by stupidity. This one's a misunderstanding. Here's the truth.
Sodium lauryl sulfate (the same as sodium dodecyl sulfate) is routinely used to solubilize chemicals used in cancer experiments prior to injecting them into test animals. Somebody read the list of substances injected, and mistook the solubilizer for the active ingredient.
I ran a search of the NIH database, and there is exactly no evidence that the detergent itself causes cancer. All the carcinogens (chemicals that clearly cause cancer) that I've heard of (and I follow this stuff) are electrophiles, protein-kinase C activators, chromosome-scramblers, and/or mitogens. I'd be extremely surprised if the simple sodium lauryl sulfate molecule is any of these things. There is an unreferenced claim attributed to a Tohuku group that lauryl sulfate causes mutations in bacteria. I could find no substantiation of this in the refereed literature. It may have been based on a misinterpretation of J. Bact. 125: 1180, 1976, in which lauryl sulfate was used in growth medium to select for bacteria which had been mutated by a standard mutagen.
Since the author of the E-mail campaign calls sodium lauryl sulfate "the cancer virus", he or she must be someone who's not gotten far in basic biology.
I have handled lauryl sulfate myself. It's a coarse powder, and a very good detergent. All soaps and detergents can irritate the eyes, and coarse powders can irritate the skin. In fact, sodium lauryl sulfate happens to be used in the standard model for skin contact dermatitis. (See the journal Contact Dermatitis 33: 1-7, 1995.) But the warnings cited for lauryl sulfate probably appear on your own powdered laundry detergent. This doesn't make either one a carcinogen.
Several anti-SLS sites mention "studies from the Medical College of Georgia" (or "The Medical College of Georgia says...") listing various supposed harmful effects of SLS on a host of tissues. The actual paper is in the obscure journal Lens & Eye Toxicity Research 6: 37-41, 1989. Several sites call this ten-year-old paper "recent research", and it actually makes no reference to any other supposed harms. Keith Green and his colleagues simply made the not-at-all-surprising observation that if there is already a chemical or physical injury to the cornea, a large concentration of the detergent slows down the healing. In his study, the group shaved pieces off the outer surface of the eyes of rabbits. Not surprisingly, pouring shampoo detergent into the eyes interfered with healing. What was more surprising is that all four of the other chemicals tested didn't.
There are now dozens anti-SLS sites online. They repeat much of the same information. As you visit them, you'll find references to a claim, twenty-one years ago, about contamination by nitrosamines; I could find nothing more current on this in the refereed literature. Since the sulfate moiety is an oxidizing agent, any nitrogen-containing compound might react to produce a tiny amount of nitrates, which in turn might react with something else to produce a nitrosamine. Your body itself produces far more sulfate just from daily metabolism, and it also produces its own nitrates. The claim on some sites that lauryl sulfate reacts with formaldehyde to produce "nitrosating agents" cannot possibly be true, since neither compound contains a nitrogen atom.
Sodium lauryl sulfate is indeed used in a model for cataract formation in the lens of the eye (J. Biol. Chem. 262: 8096-102, 1987). The experiments actually immersed the transparent lens proteins in concentrated solutions of detergent, as you would dip your own dirty clothes. It's not surprising that the proteins were altered and rendered translucent. But the lens is deep within the eye, and won't be exposed even if you splash some lauryl sulfate in your eyes. Either somebody misunderstood the work, or somebody is willfully deceiving the public.
I could not find any support in the refereed scientific literature for the allegations that lauryl sulfate prevents children's eyes from developing normally. I think that somebody just made this up.
I've spent years as part of the fight against tobacco, and have represented several plaintiffs who have been harmed by exposure to genuine industrial poisons. I become equally angry over people who expose others to substances that genunely cause cancer, and people who make money selling books that peddle groundless fear.
I am not using this page to debate the ethics of animal research, to discuss the merits of homemade soap against what you buy from a corporation, or to claim any moral high-ground beyond a fondness for truth. There may be other shampoos that are less irritating to the eyes.
Several of the anti-SLS sites also offer SLS-free cosmetics and pills for sale. You're free to draw your own conclusions.
You may use your shampoo and toothpaste without worrying about getting cancer from sodium lauryl sulfate.
Follow-up (March 2002): Since this site went up a few years back, I've found nothing else to suggest that the claims of a cancer risk are anything but hoaxes. I've also heard from about a dozen people with the same story. They had suffered from intractable aphthous ulcers ("canker sores", the white oral lesions that come and go), and got relief only by changing from a SLS-based toothpaste. This makes perfect sense biologically, and might be good for readers to know.
More follow-up (Jan 2003): In October 2002, a group in Finland looked at the ability of SLS to irritate the oral mucosa. I can't say whether this page had anything to do with this, but again is makes excellent sense. The group found betaine to be a useful agent to reduce this irritation (Act. Odont. Scand. 60: 306, 2002).
Frankly, I'm sorry that I still need to keep this page online. There is no "SLS debate". It's all obvious bunko artistry, i.e., people presenting an ever-changing target, falsifying evidence, slinging mud, and offering their readers a chance to feel intellectually and morally superior. Our world is full of this. If you can't recognize bunko artistry, you're headed for trouble in your own life. Be careful.
If you want to know who's lying and who's telling the truth, simply take a copy of this page to your local public library, and obtain the articles I've cited by interlibrary loan. Most libraries can do this. There may be a small fee, but it's worth it to find out who the crooks really are.
March 2003: I am amused to learn that BioLean, a mix of a bunch of amino acids, ephedra (be careful), and some botanicals including jujube and hawthorne berry, also contains sodium lauryl sulfate. It is promoted "to help raise overall health standards, enhance individual life extension programs, and intensify athletic performance... [and] to protect the immune system from normal, daily build-up of environmental and dietary toxins." If the anti-SLS movement had any integrity, they would be smearing the "BioLean" company as well as the shampoo people.
March 2005: The scientific literature is still utterly silent on SLS as a cause of cancer. It has become a stanard addition to skin patch tests as a prototype of a weak irritant. My neighbors at UMKC reported a case of possible SLS allergy causing desquamative stomatitis (Gen. Dent. 49: 596, 2001).
Natural-products advocate David Steinman, in "Healthy Living" magazine, reviewed lauryl sulfate. "Carcinogenic nitrosamines can form in the manufacturing of sodium lauryl sulfate or by its inter-reaction [sic.] with other nitrogen-bearing ingredients within a formulation utilizing this ingredient." This is deceptive and I've dealt with this claim above. "Although sodium lauryl sulfate is not carcinogenic in experimental studies, it has been shown that it causes severe epidermal changes in the area it is applied, indicating a need for tumor-enhancing assays." In other words, Mr. Steinman is demanding that somebody pay money so that he can play the cancer fearmonger's trump card -- ANY substance can be a promoter if you use a big enough dose. If this is the kind of person who you want to do your thinking for you, that is your business.
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