By Ewa Daniél
What is it?
Sodium Laureth Sulfate (SLES) and Sodium Lauryl Sulfate (SLS) are anionic surfactants.
An anionic surfactant is an organic substance that creates negatively charged particles when they are dissolved in water, in that way an active washing component (the anion) is created.
SLES and SLS are among the most common surfactants used in cosmetics and detergents. You will often find them used as emulsifying cleaning agents in household cleaning products such as laundry detergents, spray cleaners, and dishwasher detergents and in cosmetics rinse off products such as shampoo and bodywash.
What is the problem?
When it is written on a shampoo that it is “without sulfate” or “sulfate free” then it’s typical the SLES and SLS that is referred to, since these sulfates have a bad reputation.
Used as tensides SLS and SLES´s main function is to rinse and remove dirt, fat and grease, which they are very effective at, but when they are used in leave on products such as a bodylotion the properties that make them very effective tensides, have the opposite effect, since they can remove the natural fats from the skin and they are thus likely to irritate our skin.
This side effect can be seen in leave on products and not rinse off products.
Apart from the skin irritating properties, there are (like with parabens and Phenoxyethanol) many rumors when it comes to SLS and SLES. These rumors tend to make us believe that the sulfates can cause cancer, blindness and hair loss when they are used in a shampoo containing sulfate.
The perception that SLS is carcinogenic is often based on studies that use the ingredient as a vehicle substance to test the carcinogenicity of other agents. An article written by Birt et al commonly is cited as supporting the carcinogenicity claim for SLS. However, this is another example of public misinterpretation and the resulting dissemination of inaccurate information. In the study by Birt et al. SLS was used as a vehicle to process the agent being tested. No evidence supporting the carcinogenic effect of SLS was reported.
What does the experts say?
The Cosmetic Ingredients Review / CIR is an established seven-member Expert Panel comprised of individuals experts in dermatology, pharmacology, chemistry, and toxicology – these independent scientists and physicians perform reviews.
CIR has thus assessed both SLES and SLS twice.
CIR about SLS
“Information circulating around the Internet has raised questions about the safety of SLS (Sodium Lauryl Sulfate). The Cosmetic Ingredient Review (CIR) has fully assessed the safety of this ingredient and found it to be safe”
CIR about SLES:
“Sodium Lauryl Sulfate appear to be safe in formulations designed for discontinuous, brief use followed by thorough rinsing from the surface of the skin. In products intended for prolonged contact with skin, concentrations should not exceed 1 %
Nor SLS or SLES are known to be allergenic or be sensitizers (NICNAS, 2003; NICNAS, 2007; OECD, 2007; REACH).
According to the textbook “monographs in contact allergy” vol. 1 contact dermatitis to SLS is very rare:
“contact allergy to SLS -if it exists at all (well documented and proven cases of contact allergy have not been reported) -is extremely rare”
Contact allergy to these agents (SLES) has been reported but this was mainly due to highly allergenic contaminant.
There is no scientific evidence supporting that SLS or SLES should be a carcinogen. None of them are classified as carcinogenic in the European Chemical Agency/ECHA register. Nor are they listed as a carcinogen by the International Agency for Research on Cancer (IARC); U.S. National Toxicology Program; California Proposition 65 list of carcinogens; U.S. Environmental Protection Agency.
In Australia, the National Industrial Chemicals Notifications and Assessment Scheme (NICNAS) reviewed studies on the safety of sodium lauryl sulfate. It found only one study designed to examine the carcinogenic effects of sodium lauryl sulfate. This study found that sodium lauryl sulfate was not carcinogenic in dogs. NICNAS also found that even at high doses, sodium lauryl sulfate had no effect on fertility.
The American Cancer Society writes on their website that SLS aren’t known carcinogens
Like most detergent SLS can be irritating to the eye when it is used in high concentrations, the ingredient is a classified eye irritant and studies show that it can be irritating if it is used in concentration higher than 1-2 % in leave on product.
But the fact that it should cause blindness and damage the eyes is not correct. The rumor occurred because of a study published by Green et al. The study showed that high concentrations of SLS in the eyes after an eye damage can slow the healing process. Unfortunately, this study was misinterpreted and caused both media and some people to claim that SLS can cause eye damage and blindness, even though the study doesn’t say anything about this. In an interview Dr.Green has stated that his results have been misquoted and the claims are not supported by his findings.
Several studies show that both SLS and SLES are safe to use in rinse off products. The exposure in these kind of products is very low since they are washed off and producers of shampoo and soap add ingredients such as glycerin that add moisture and fat so that the final product won’t be irritating to skin. They are thus found safe to use and producers are allowed to use them in AllergyCertified rinse off products.
Beringer J et al Hospital laundries and their role in medical textiles Handbook of Medical Textiles, 2011
Birt DF et al, Inhibition by dieatary selenium of colon cancer induced in the rat by bis (2-oxopropyl) nitrosamine, Cancer res 1982; 42:4455-4459
Bondi C. AM et al “Human and Environmental Toxicity of Sodium Lauryl Sulfate (SLS): Evidence for Safe Use in Household Cleaning Products” November 2015
Cosmetic Ingredient Review (CIR), Final report on the safety assessment of sodium lauryl sulfate and ammonium lauryl sulphate. Int J Toxicol. 1983;2(7):127–81.
Cosmetic Ingredient Review (CIR) Final report on the safety assessment of sodium lauryl sulfate and ammonium lauryl sulfate. Int J Toxicol. 2005;24(1):1–102.
De Groot A.C, Non -fragrance allergens in Cosmetics part 1&2, Monographs in Contact Allergy volume 1
Green K. et al Preservatives on the healing rate of rabbit corneal epithelium, Lens eye Toxic res. 1989: 6:37-41
Horwath-Winter J. et al “Cytotoxicity Evaluation of Soft Contact Lens Care Solutions on Human Conjunctival Fibroblasts” Ophthalmologica 2004;218:385–389
Robinson V.C et al Final report of the amended safety assessment of sodium laureth sulfate and related salts of sulphated ethoxylated alcohols.
Int J Toxicol. 2010 Jul;29(4 Suppl):151S-61S.
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NICNAS Sodium, ammonium and potassium lauryl sulfate: Human health tier II assessment https://www.nicnas.gov.au/chemical-information/imap-assessments/imap-group-assessment-report?assessment_id=184