SLS, SLES & Sulfates

Nearly 100% of our new customers say “we do not want to use Sodium lauryl sulfate (SLS) Sodium laureth sulfate (SLES) and no to all SULFATES”. We are happy to comply and want to explore the topic a bit further.

There is so much information on the internet about the dangers but regrettably most of it is erroneous due to a basic misinterpretation of scientific data and perhaps a desire to capitalise on what could be seen as a marketing opportunity.

This is particularly true of Sodium Lauryl Sulfate (SLS). One of the primary issues is that this material, since its inception in the 1940’s, has been used in so many areas, both industrial and cosmetic. This myriad of products means various concentrations have been employed which will all have different effects on the skin and body. It appears that this has not been understood. A shampoo for example will have a much lower level and employ a finer grade than a floor cleaner and a toothpaste will probably have 100 times less and will probably use a pharmaceutical grade.

The main concerns appear to be:-

  • Ocular irritation
  • Dermal irritation
  • Oral toxicity
  • Carcinogenicity
  • Organ toxicity
  • Hair loss
  • Skin sensitization

In addition there are concerns over aquatic toxici and biodegradability.

This is a long list so I will address each individually:

Ocular Irritation (eye irritation)

Like most cleansing agents SLS can be irritating to the eye in high concentrations but there is no evidence that it can cause permanent damage, blindness or cause cataract formation. These claims have been made and were based on the misinterpretation of two reports. The first point to a study by Green et al published in the journal “Lens and eye toxicity research”. Dr Green’s paper does not suggest that SLS causes ocular damage or blindness but a leading cosmetic company promoting its SLS free campaign not understanding and misquoting the information caused a media storm which led to the following response from legal council,

…your citation of his work was not simply a misinterpretation, it was plainly wrong. By citing his research in support of erroneous conclusions, you have libeled Dr. Green. In fact, [you have] even attributed quotations to Dr. Green which he has never written or spoken, and which he would not ever write or speak”

In this case, the dissemination of misconstrued results not only provided a disservice to the general public but also caused serious repercussions for the scientific researchers.

A second erroneous ocular health claim made about SLS is its link to cataract formation.  Claims about SLS causing cataract formation appear to cite a 1987 study in the Journal of Biological Chemistry.

It should be noted that the anatomy of the eye renders direct exposure of the lens to SLS impossible, as it is deep within the eye protected by the cornea, and therefore, not vulnerable to exposure through typical consumer product usage. As such, a causal relationship between SLS in consumer products and cataract formation is not scientifically supported.

Dermal Irritation (skin irritation)

Like most surfactants if left on the skin in sufficiently high concentrations SLS can cause irritation and some peoples skin will react more than others. Indeed Human patch tests (typically a 24-hour exposure) confirm that SLS concentrations of more than 2% are considered irritating to normal skin. However SLS is generally used in wash off products like shampoo so contact with the skin is likely to be minutes not hours and with added water the concentration could easily be less than 2% in any case. So in normal foreseeable use SLS is not a skin irritant

Oral Toxicity (ingestion)

In high concentrations SLS could be toxic if ingested but it is important to note it is not as toxic as common salt which we eat every day so this is not really an issue at all.

Carcinogenicity (causes cancer)

The most egregious claim by far is that SLS is carcinogenic. The origin of this claim is uncertain, but it is likely to have derived from multiple misinterpretations of the scientific literature. There is no scientific evidence supporting that SLS is a carcinogen. SLS is not 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; or the European Union.

The perception that SLS is carcinogenic is often based on studies that use the ingredient to evaluate the carcinogenicity of other agents. It is apparent that the common use of SLS as a solubilizing agent in toxicology studies has led to the public’s confusion around the chronic toxicity of SLS.

Other claims denouncing SLS as a carcinogen point to a chemical reaction between SLS and formaldehyde that creates nitrosamines as a by-product. However, it is not possible for SLS and formaldehyde to react and form a nitrosamine. Nitrosamines contain two nitrogen atoms, but neither SLS nor formaldehyde contain nitrogen atoms. Therefore, the two cannot react to form a nitrogen-containing nitrosamine. Although nitrosamines have been associated with several types of cancer and many are classified as known, possible, or probable carcinogens they cannot be associated with the presence and use of SLS

Organ Toxicity (damage to liver, kidneys etc.)

It is often claimed that SLS “absorbs into the blood stream, builds up in the heart, liver, lungs and brain, and causes damage”. Claims of this nature often cite the Cosmetic Ingredient Review (CIR) Final Report on the safety of SLS, which contains an extensive review of the absorption and excretion of SLS in humans and animals. However, the CIR concludes that while SLS can be absorbed through the skin when applied directly, the majority of the material remains in or on the skin surface. If SLS is absorbed into the bloodstream it is quickly metabolized by the liver into more water-soluble metabolites that are rapidly excreted. There is no evidence that supports the accumulation of SLS in vital organs and associates it to systemic toxicity or vital organ damage. As such, accusations that SLS will bioaccumulate in humans and cause organ damage are inaccurate

Hair Loss

The same CIR report  is also cited as supporting the claim that SLS can cause hair loss and baldness as is a study published in 1998 by the European Journal of Dermatology . Whilst both studies identified the deposition of SLS on the root sheath of the hair follicle they did not draw conclusions about the effects of this deposition on the hair. Neither study suggests that SLS is responsible for, or contributes to, chronic hair loss. In general claims that associate the use of SLS-containing products with hair loss are not scientifically supported.

Skin Sensitization

Another unsubstantiated claim about SLS is that it can cause severe dermal sensitization. A sensitizer is a substance that causes hypersensitivity through an allergic or photodynamic process, which becomes evident on reapplication of the same substance on the skin. There is no scientific evidence to support that SLS has sensitization potential. SLS is not included on any lists of known or suspected sensitizers. Therefore, stating that SLS is a sensitizer is inaccurate.

Aquatic Toxicity (water contamination)

Aquatic toxicity refers to the short-term adverse effects that result from the exposure of aquatic life to a chemical or formulation.

SLS as with other chemicals/surfactants at full strength is moderately toxic to aquatic life but product formulations contain dilutions of SLS that are not necessarily moderately toxic and, in fact, can be nontoxic to aquatic life.

By the time cleaning product ingredients reach natural waters, they are mostly degraded.


The ability of a chemical to decompose into simple, nontoxic components under ambient environmental conditions within a short period of time (typically 96 hours) means that it is biodegradable. SLS is readily biodegradable under aerobic and anaerobic conditions and, therefore, does not persist in the environment and is therefore environmentally benign.

Sodium laureth sulfate SLES is also used extensively in the cosmetic industry and suffers the same fate as SLS. Many of the issues are the same particularly that this material will cause cancer. In this case it is generally because there is an additional chemical process employed, that of ethoxylation. This means that the material is reacted with ethylene oxide which has the potential to form dioxanes. 1,4-Dioxane is a known carcinogen. Because of this the amount of dioxane in SLES are closely monitored and has been limited to 10ppm (parts per million) with is 0.001%. 10ppm is the level considered safe for all cosmetics by the SCCS (Scientific Committee on Consumer Safety). So there is still likely to be a small amount of a cancer causing agent in this base. But let’s put this in perspective:

  • The allowable level in food stuffs that is considered safe by the WHO (world health organisation) is also 10ppm and SLES is not normally ingested.
  • SLES is diluted during use so the levels are potentially a lot lower.
  • 1,4-Dioxane in the air at 100ppm is considered acceptable.

What is wrong with sulfates?

A sulfate is a salt or ester of sulphuric acid. Probably the most common sulfate is Epsom Salts which chemically is Magnesium sulphate (sulfate). This is a natural material found in sea water, natural springs and mineral deposits. So why are sulfates bad for you? Well basically they are not. Once again it is just a misinterpretation of scientific data. It appears that because sodium lauryl sulfate and sodium laureth sulfate have been so misunderstood and the both contain the word sulfate then all sulfates must be bad.

I think it important to remember that if you choose not use these much maligned products you have to find replacements. The question is are the replacements any better as many have the same issues.

One ingredient you may choose to use is betaine. Betaines and Sultanes, which a chemically similar, are often used in baby shampoos. In 2004 Cocoamidopropyl betaine (CAPB) was described by the American Contact Dermatitis Society as “allergen of the year”. It has been linked to all the same issues as SLS/SLES. E.g. Skin and Eye irritation. You could use an Alkyl glucoside (e.g. coco glucoside). These too have been linked to allergic dermatitis etc. The point is that pretty much all surfactants at full strength can be irritating and damage the skin but if used at the right levels and formulated correctly they are perfectly safe.

SLS & SLES are used by most major brands (and this includes major “natural” brands) Examples are Lush, Aesop, L’Occitaine and Aveda to name just a few. They are a commodity so they are very cost effective. They are incredibly efficient so you can use really low levels. Replacements can cost up to 10 times as much and you very often have to use a lot more to achieve the same result.

If you choose to avoid SLS and SLES remember that Ammonium lauryl sulfate , Ammonium laureth sulfate, Sodium myreth sulfate or Sodium coco sulfate have exactly the same properties. Lather is not vital to cleanse the hair but it does help. A rich, creamy lather is not only enjoyable to use, but also helps the cleansing agents to spread easily across your scalp, in-between fibres and down the length of your hair. Something to consider when trying to appeal to the consumer who equate quality cleansing with a high foaming product.





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