SLS and SLES in Shampoos and Cleansers: What the Evidence Says

SLS and SLES in Shampoos and Cleansers: What the Evidence Says

Sodium lauryl sulfate (SLS) and sodium laureth sulfate (SLES) are two of the most widely used surfactants in personal care products. They create the lather consumers associate with cleansing effectiveness — and they also generate more consumer concern than almost any other routine cosmetic ingredient category.

This guide separates the established evidence from the overstated claims, and gives you a practical framework for deciding whether to seek sulfate-free alternatives.

Note: This article provides consumer product information. It is not medical advice. Consult a dermatologist for advice on managing specific skin conditions.

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What Are SLS and SLES?

Sodium Lauryl Sulfate (SLS) — INCI: Sodium Lauryl Sulfate An anionic surfactant derived from either petroleum or coconut/palm oil. It disrupts the surface tension of water, allowing oils, sebum, and dirt to be rinsed away. It is also used in scientific research as a positive irritant control — meaning it is deliberately used to cause mild skin irritation in controlled studies.

Sodium Laureth Sulfate (SLES) — INCI: Sodium Laureth Sulfate A derivative of SLS that has been ethoxylated (reacted with ethylene oxide). Ethoxylation makes SLES milder and less irritating than SLS, with better skin compatibility. However, the manufacturing process can introduce trace amounts of 1,4-dioxane as a byproduct.

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What the Evidence Actually Shows

Skin irritation: established for SLS, dose-dependent

SLS is a well-documented skin and mucous membrane irritant at concentrations typically used in rinse-off products (5–30%). This irritancy is the basis for its use as a positive control in patch testing. The Cosmetic Ingredient Review (CIR) Expert Panel reviewed SLS and concluded it is safe in rinse-off products at concentrations up to approximately 1%, but that leave-on concentrations require additional safety data. Most shampoos use SLS at 4–15%.

For people with eczema (atopic dermatitis) or a compromised skin barrier, there is good clinical evidence that SLS can worsen symptoms. A 2002 study in Contact Dermatitis found that SLS disrupted the skin barrier in atopic patients significantly more than in healthy controls. This is a clinically relevant finding for a subset of consumers — not the general population.

1,4-Dioxane in SLES: a real but regulated concern

As noted above, SLES manufacturing can produce trace 1,4-dioxane contamination. The IARC classifies 1,4-dioxane as possibly carcinogenic to humans (Group 2B). The EU requires that cosmetic products contain 1,4-dioxane as low as technically achievable, and the FDA monitors levels through its Voluntary Cosmetic Registration Program. The US state of New York passed a law in 2022 requiring 1,4-dioxane to be below 1 ppm in cosmetics.

For products sold in the EU or complying with the EU Cosmetics Regulation, 1,4-dioxane contamination is addressed through good manufacturing practice and quality testing requirements.

What is not supported by evidence:

• SLS causing cancer — no peer-reviewed evidence supports this
• SLS causing systemic toxicity at cosmetic use levels — bioavailability from rinse-off products is negligible
• SLES being "dangerous" for the general population — at permitted concentrations in rinse-off products, SLES has a well-characterised safety profile

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Regulatory Status

Jurisdiction	Status
US FDA	Permitted; CIR concludes safe in rinse-off formulations
EU Cosmetics Regulation	Permitted; 1,4-dioxane in SLES must be minimised per good manufacturing practice
New York State (2022)	1,4-dioxane ≤1 ppm requirement in cosmetics
EU REACH	Not classified as an SVHC; no restriction

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Who May Benefit From Sulfate-Free Products

The evidence most strongly supports sulfate-free choices for:

• People with eczema or atopic dermatitis — clinical evidence that SLS can exacerbate barrier disruption in this population
• People with sensitive or reactive skin — individual tolerance varies; sulfate-free options may reduce irritation
• Colour-treated hair — SLS strips colour faster than gentler alternatives; a practical (not safety) reason to choose sulfate-free
• Very dry or curly hair — SLS removes natural oils; hair that benefits from retained moisture may do better with gentler surfactants

For healthy skin and hair without specific sensitivities, the evidence does not demonstrate a safety advantage to sulfate-free products. This is a preference and tolerance question, not a clear-cut safety issue.

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Gentler Surfactant Alternatives

If you prefer to avoid SLS or SLES, look for these alternative surfactants on ingredient lists:

Alternative	INCI Name	Characteristics
Cocamidopropyl betaine	Cocamidopropyl Betaine	Amphoteric; significantly milder than SLS; derived from coconut oil
Decyl glucoside	Decyl Glucoside	Non-ionic; very mild; good for sensitive skin and baby products
Coco-glucoside	Coco-Glucoside	Non-ionic; plant-derived; mild
Sodium cocoyl isethionate	Sodium Cocoyl Isethionate	Mild; good foam despite lower irritation
Sodium lauroyl sarcosinate	Sodium Lauroyl Sarcosinate	Mild; often used in "natural" products

Note that "sulfate-free" does not mean "allergen-free" or "irritant-free" — some people react to cocamidopropyl betaine, for example. Label checking remains important even with gentler formulations.

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Reading Labels

• Look for SLS as: Sodium Lauryl Sulfate
• Look for SLES as: Sodium Laureth Sulfate or Sodium Lauryl Ether Sulfate
• Look for concentration position — if listed 3rd–5th in a shampoo, it is a primary ingredient; if near the bottom of a long list, concentration is lower
• "Sulfate-free" on packaging is a useful indicator but does not guarantee the product is free from all potential irritants

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ScoreKart identifies SLS and SLES in scanned products and flags their position in the ingredient list, helping you compare sulfate concentrations across products.