Synonyms: sodium dodecyl sulfate, dodecyl sodium sulfate, SLS, lauryl sodium sulfate, sodium laurylsulfate, sulfuric acid monododecyl ester sodium salt.

The chemical formula is C12H25NaO4S, giving a molecular weight of 288.38 grams per mol. Sodium Lauryl Sulfate is useful in a wide variety of personal care applications in which viscosity building and foam characteristics are of importance. Because of its low salt content, this product is particularly useful in formulations that are sensitive to high levels of sodium chloride. It can be incorporated into shampoos, handsoaps, bath products, shaving creams, and medicated ointments.

A chemical found in mainly shampoos, toothpastes, and liquid soaps, for the general public, and it is primarily used for its ability to promote easy lather. The chemical has been known to strip down the top layer of skin, the epidermis, which aids in sealing in of water moisture. The chemical has also been proven to have the ability, with prolonged exposure, to dry out and dull the hair shaft. Also known to wash out the color from dyed hair. Most alternatives for sodium lauryl sulfate are sodium laureth sulfate, ammonium laureth sulfate, and ammonium lauryl sulfate. All the chemicals mentioned are also cleansers with the ability to promote lather easily, and are usually the main ingredient, second only to water, in the products in which they are used. The best way to know if these ingredients are used in your products is to read the ingredient list. There are also organic alternatives used in botanic products, and then none of the chemicals listed above should appear.

The chemical is also used as an agent in industrial strength cleaners for its cleansing ability. The main reason this industrial strength cleanser is used in personal care products is its ability to promote foam and lather easily. Most consumers visually associate lathering with clean, and therefore prefer shampoos and soaps that lather easily. Shampoos containing fatty acids, found in lipids, have been shown to help cleanse the hair just as affectively as sodium lauryl sulfate, but do not create the same amount of lather. Some products use both sodium lauryl sulfate and fatty acids to effectively cleanse hair.

This chemical has also been proven to be rather effective in the prevention of spreading specific STDs/STIs . The chemical has been shown to provide levels of protection against HIV, chlamydia, herpes type 1 and 2, and gonorrhea. This has thus far been proven on laboratory mice and is currently being tested on women, in the form of a microbicide liquid, in clinical trials. Sodium lauryl sulfate may one day be used as a mainstream way of preventing the spread of these diseases in humans.

This being said, sodium lauryl sulfate has not been positively proven dangerous in any shape or form. The only negative effect this chemical may have on the body is a drying of the skin, hair, and sometimes nails. Although results have been observed, discontinuing use of products with this chemical may or may not help improve moisture.

Part 1: SLS and cancer

Sodium lauryl sulphate (SLS for short) has been the target of a cancer scare for more than a decade; I remember seeing a mimeographed copy of a letter that warned about a link between SLS and cancer long before the advent of the Information Superhighway.

Now that Xerox copies are obsolete, it's not unusual to receive an e-mail version of the warning.

The actual text varies and mutates, like all good memes do, but the following list gives a good summary of the "facts" that everybody should be aware of:

  1. SLS is found in most brands of shampoo and toothpaste;
  2. it is used to scrub garage floors;
  3. it is a known carcinogen;
  4. it is used as a pesticide;
  5. it is an irritant;
  6. a phone call to a shampoo manufacturer elicits the following admission: "We know that SLS causes cancer, but there is nothing we can do because we need that substance to produce foam."

The letter usually contains a list of "good" brands that don't use SLS in their products.

Part 2: Trusted sources

Item 6) in the above list sent off-scale my hoax warning system, but the text is usually peppered by other incongruences. I've surfed some sites to check the claims:

My opinion is that the warning is a hoax, even if it's put together more cleverly than usual: it's a good mix of truths, half-truths and outright lies, the hallmark of all believable urban legends.

Part 3: Facts and fiction

The following list addresses the claims one by one:

  1. SLS is indeed found in shampoos, toothpastes and several other products (including the nimesulide that I've taken while writing this). It is indeed a good surfactant and a strong foaming agent, and it's also cheap. Status: TRUE.
  2. Industrial strength cleaners contain high concentrations of SLS, because garage floors are quite dirty and hard to clean. The percentage of SLS found in personal care products is far lower. Status: TRUE - SORT OF.
  3. The FDA lists SLS as a food additive, and considers it Generally Recognized as Safe or GRAS (21 CFR 172.882). The American Cancer Society clearly states that SLS and its other compounds are known irritants, not known carcinogens (they also debunked the hoax in one of their web pages). The final report on the safety assessment of SLS found in the toxnet site concludes that in mutagenesis studies, rats fed 1.13% and 0.56% SLS in the diet for 90 days produced no more chromosomal aberrations or clastogenic effects than did a control diet. (Those guys are sick. I won't tell you how they tested SLS on rabbits. Still no cancer, though.) Status: FALSE.
  4. I've been able to track down only one pest control product that lists SLS as its active ingredient: "Dr. Dogkatz Critter Chaser" - a pet shampoo. Moreover, SLS employs a non-toxic mode of action in controlling fleas and ticks (I suspect that its surfactant properties effectively smother insects). This doesn't mean that SLS isn't used along with pesticides to improve their effectiveness: a drop of SLS-laced parathion will have less surface tension, and will be more readily absorbed by the unlucky bug. Other common chemicals, such as caffeine or nicotine, are used as pesticides. Status: MISLEADING, IRRELEVANT.
  5. SLS is an irritant, as anybody who got foam in his eyes can testify. While filming The Pink Panther, Robert Wagner was temporarily blinded by an industrial strength foaming agent used in the bathtub scene; I suspect that SLS was involved. Several articles listed in the toxnet site confirm that rinsing with water will take care of the irritation, with no lasting side effects. Other common chemicals, such as capsaicin or table salt, are even more powerful as irritants. Peeling onions will get sulfuric acid in your eyes. Status: MISLEADING, IRRELEVANT.
  6. The tobacco companies denied for decades that cigarette smoke causes cancer, but in this case we are led to believe that a simple phone call settles the matter. Note that there are several other foaming agents available, so there is no reason to stick to a known carcinogenic. If all else fails, you don't actually need foam to make a good shampoo; customers associate lots of bubbles with a cleaner effect, but the two things are almost unrelated. Status: CLEARLY FALSE.

Part 4: Birth of a hoax

This is entirely my opinion, but... who created the hoax? The original author might have thought that scaring lots of people was funny (remember, SLS is really ubiquitous), but I suspect that some companies used it as free advertising to push their products.

They just had to mix a shampoo formula that doesn't contain SLS, put it in the list of "good, natural personal care products" and let the meme machines do the rest. Probably they also raised the price of those shampoo bottles: they are the good guys fighting against cancer mongers, after all...

Different points of view are welcome. Different points of view supported by reputable sources are especially welcome.

The hidden dangers in your daily care products: SLS and SLES

Two ingredients that can be found in nearly every product in your bathroom are sodium lauryl sulphate (SLS) and sodium laureth sulphate (SLES). Typically, they are the second and/or third ingredients in the list following water. These ingredients are the ones that cause shampoo, soap, bubble bath, shower gel, etc. to foam, which explains their use in these types of products. SLS and SLES are also cheap detergents that would no doubt be pleasing to company owners.

Here’s the problem:

Both SLS and SLES are anionic surfactants (anionic referring to the negative charge that both chemicals have) and they may be contaminated with nitrosamines, which are carcinogenic. These chemicals are also very corrosive and used in car washes, as garage floor cleaners and engine degreasers because of their extreme effectiveness in removing oily stains and residues. In addition, the Material Safety Data Sheet (MSDS) classified both chemicals as moderate to server eye and skin irritants.

SLS and SLES dissolve grease on car engines in the same way that they dissolve the natural oils on your skin, leading to a drying effect. These chemicals also change the natural qualities of skin proteins, causing irritation and allowing environment contaminants easier access to the lower, more sensitive layers of the skin.

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