What are they?

Sodium Laureth Sulfate (SLES) and Sodium Lauryl Sulfate (SLS) are anionic surfactants, meaning they are cleansing agents that form negatively charged particles when dissolved in water. This makes them highly effective at removing dirt, grease, and oils.

SLES and SLS are among the most commonly used surfactants in both cosmetics and household detergents. They are frequently found in:

• Laundry detergents

• Dishwashing liquids

• Household spray cleaners

• Rinse-off cosmetic products such as shampoos, soaps, and body washes

They are mainly used for their ability to create foam and provide strong cleansing properties.

What is the concern?

Many products marketed as “sulfate-free” specifically refer to the absence of SLS and SLES, as these ingredients have developed a negative reputation.

The primary function of SLS and SLES is to remove dirt, fat, and grease. While they are very effective cleansers, this strong cleansing action can also remove natural lipids from the skin.

This is particularly relevant for leave-on products such as body lotions, where prolonged skin contact may lead to irritation.

In contrast, rinse-off products such as shampoos and soaps are washed away quickly, resulting in much lower exposure.

Myths and misconceptions

Like parabens and phenoxyethanol, SLS and SLES have been surrounded by various rumors, including claims that they cause cancer, blindness, or hair loss. It is striking that people believe manufacturers would add a substance that causes hair loss, which would likely not result in long-term shampoo sales.

It is important to note that these claims are not supported by scientific evidence.

The perception that SLS is carcinogenic often stems from a misunderstanding of studies in which SLS was used solely as a vehicle substance to test other compounds.

For example, the study by Birt et al. is sometimes cited as evidence of carcinogenicity, but SLS was not the substance being tested, and no carcinogenic effect of SLS was reported.

What do experts say?

The Cosmetic Ingredient Review (CIR) is an independent scientific panel consisting of experts in dermatology, pharmacology, chemistry, and toxicology.

CIR has reviewed both SLS and SLES multiple times.

CIR statement on SLS:

“Information circulating around the Internet has raised questions about the safety of SLS. The Cosmetic Ingredient Review (CIR) has fully assessed the safety of this ingredient and found it to be safe.”

CIR statement on SLES:

“Sodium Laureth Sulfate appears 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 (leave-on), concentrations should not exceed 1%.”

Allergy and sensitization

Neither SLS nor SLES is considered a common allergen or sensitizer

(NICNAS, OECD, REACH).

According to Monographs in Contact Allergy, true contact allergy to SLS is extremely rare:

“Contact allergy to SLS, if it exists at all, is extremely rare, and well-documented cases have not been reported.”

Reported reactions to SLES have mainly been linked to impurities or contaminants rather than to the ingredient itself.

Carcinogenicity

There is no scientific evidence that SLS or SLES is carcinogenic.

Neither ingredient is classified as carcinogenic by:

• The European Chemicals Agency (ECHA)

• The International Agency for Research on Cancer (IARC)

• The U.S. National Toxicology Program

• California Proposition 65

• The U.S. Environmental Protection Agency

NICNAS concluded that sodium lauryl sulfate was not carcinogenic in animal studies and showed no effects on fertility, even at high doses.

The American Cancer Society also states that SLS is not a known carcinogen.

Eye irritation and the blindness myth

Like many detergents, SLS can irritate the eyes at high concentrations and is classified as an eye irritant.

However, the claim that it causes blindness is incorrect.

This myth originated from a study by Green et al., which showed that very high concentrations of SLS in damaged eyes could slow healing.

The study did not conclude that SLS causes blindness, and Dr. Green later stated that the results had been misquoted.

AllergyCertified assessment

AllergyCertified toxicologists have assessed SLS and SLES through risk assessment.

Both SLS and SLES are considered safe for use in detergents and rinse-off cosmetic products, particularly when formulations include moisturizing ingredients that reduce irritation potential.

For leave-on cosmetic products, stricter criteria apply due to prolonged exposure. In such products, SLS and SLES are only allowed as additives in raw materials and only at very low concentrations, where they are considered safe and unlikely to cause irritation.