Sunday, 6 June 2010

Myth or Fact: SLS is an irritant?

Yes this is a fact. SLS like most detergents* is an irritant.

What is an irritant?
An irritant in this case is a substance that creates discomfort such as itching, reddening of the skin or dryness. Most detergent based irritants have short lived effects (minutes to under an hour) but a small minority of people have severe reactions.

Why are detergents irritating?
I will have to transport you back to the original post in this series. There, I explained that SLS dissolves oil from the surface of hair and skin. With this oil barrier gone, the surface of the skin is more susceptible to water loss causing it to become dry. The dryness can then trigger itching which then in turn triggers redness.

Is this irritation damaging?
No the irritation is generally not damaging, just a way of letting you know that the skin is lacking oil (prompting you to apply a cream or oil to the surface). Studies done on skin indicate that the oil barrier is temporarily disturbed but does not affect the ability of cells to multiply and grow as normal. (Archives of Dermatological Research, pp615-620,1998)

When can the irritation be damaging?
Eyes are a particularly sensitive surface. For example a gas produced while cutting onions can trigger tears. SLS too can trigger tears but can also damage the eye surface if kept on for long enough. This is why when using ANY shampoo (sulfate free, tear free formulae included and soap!) it is wise to avoid your eyes and rinse immediately with copious amounts of water.

SLS can be extremely damaging to skin if used in high concentrations (such as that used in laboratories NOT I STRESS NOT in shampoo). Also failure to rinse off SLS can cause serious irritation.

How can irritation be reduced?
The simplest method is application of an oil prior to use and immediately after use. 

Good lab tested shampoos also have a host of very sophisticated anti irritancy methods such as pH control , combination of surfactants, control of molecular size and addition of chemical anti irritants (J. Soc. Cosmet. Chem, pp 667-679,1977).

*Cocobetaine (cocoamidopropyl betaine, cocamidopropyl betaine) a popular SLS substitute is also an irritant and similar to SLS can cause contact dermatitis (Contact Dermatitis, pp 419-422, 2006). All surfactants which act to dissolve oil have the potential to cause irritation. Essentially the irritation is not about the substance applied, but rather its effect (i.e no or reduced oil on skin = water loss = dryness=irritation).


  1. I see your saving the cancer question for last. Can't wait! Love the series!

  2. I thought sodium lauryl sulffate (SLS )was irritant but not sodium laureth sulfate ( SLES) , at least not as much. Then years ago, i was using herbal essence and it caused a lot to itchiness. I then switched to sodium laureth shampoos and the itchiness stopped.

    This is what paula begoun says on her site :

    ''Despite the myths about SLS causing cancer and other health problems being false, sodium lauryl sulfate should be avoided because it is a potent skin irritant. In contrast, sodium laureth sulfate is not an irritant because it has a different chemical structure that results in a gentler cleansing agent.

    SLS is considered a standing comparison substance for measuring skin irritancy of other ingredients. In scientific studies when they want to establish whether or not an ingredient is problematic for skin, they compare its effect to the results of SLS. In amounts of 2% to 5% it can cause irritating or sensitizing reactions in lots of people (Sources: European Journal of Dermatology, September-October 2001, pages 416-419; and American Journal of Contact Dermatitis, March 2001, pages 28–32). But irritancy is not the same as the other dire, erroneous warnings floating around the Web about this ingredient! ''

    She also said : ''Sodium lauryl sulfate can be a potent skin irritant. Therefore, it is better for skin if it either wasn't in the product or at the end of the ingredient list to assure that it is in a small enough a concentration to reduce any risk of irritation. But in terms of any other health or disease problem, there is none.''

  3. Practically all detergents and soaps are irritants Kadiane. Remember irritancy is about stripping the oil layer during the cleaning process causing the skin to lose water (then comes the dryness, itchiness and redness).

    SLS is an excellent surfactant and therefore strips off most of the oil on the surface (this is why it is useful in shampoo). SLES is also quite a good surfactant but certainly the ethoxylation process that I discussed in the cancer myth post DOES make it less irritating.

    However it would be incorrect to say that it is non-irritating because any surfactant (and we can include soap too) that can remove oil or disrupt the oil barrier from the surface of skin ultimately is a potential irritant.

    Irritancy is a description of skin feeling dry and possibly itchy after use of a product.

    Just as further proof - Contact Dermatitis, pp 26 - 32, 2003 - (They found SLES is indeed less irritating than SLS. Note, the word is less irritating not non-irritating. Irritancy with SLS lasted 10 days while with SLES lasted 7 days) So yes SLES is a much milder irritant.

  4. I love this series! This post, and the comments, have helped me clearly understand the reason most shampoo makes me so itchy and uncomfortable - for days. Thanks.

  5. Are there any suitable alternatives to SLS aside from cowashing. What are some safe ingredients that clean without overstripping or are less irritating that SLS?


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