Introduction to Sodium Laureth Sulfate (SLES)
Sodium laureth sulfate (SLES), also called sodium lauryl ether sulfate, is the anionic surfactant that forms the backbone of the great majority of shampoos, body washes, hand soaps, toothpastes and liquid cleaning products. It is an alkyl ether sulfate: a fatty alcohol that has been ethoxylated and then sulfated and neutralised. The ethoxylation step is what distinguishes SLES from the simpler sodium lauryl sulfate (SLS) and makes it generally milder and more soluble.
For buyers, the essential facts about SLES are its identity and CAS, the meaning of the “N2EO” designation, the specification of the standard 70% paste, the ethoxylation-plus-sulfation production route, and the quality issue that distinguishes good SLES from poor — the 1,4-dioxane content. This article covers all of these, along with the surfactant behaviour, applications and sourcing of SLES.
PolyBlueChem can supply SLES 70% (CAS 9004-82-4); see the product page for the current specification.
Chemical Identity and Structure
SLES is the sodium salt of a sulfated fatty alcohol ethoxylate. Its structure is R–(OCH2CH2)n–OSO3Na, in which R is a fatty (lauryl/myristyl) alkyl chain, the –(OCH2CH2)n– is a short polyethylene oxide chain, and the –OSO3Na is a sulfate group. The molecule therefore has a hydrophobic tail (the alkyl chain), a short hydrophilic ethoxylate spacer and an anionic sulfate head.
| Property | Value |
|---|---|
| Common names | Sodium laureth sulfate (SLES); sodium lauryl ether sulfate |
| Chemical type | Sodium alkyl ether sulfate (anionic surfactant) |
| CAS number | 9004-82-4 (also listed as 68585-34-2) |
| General structure | R–(OCH2CH2)n–OSO3Na (R = C12–C14 alkyl) |
| Ethoxylation (this grade) | Approx. 2 EO units (N2EO) |
| Appearance (70%) | White to yellowish paste |
Because SLES is a mixture (a distribution of alkyl chain lengths and of ethoxylate chain lengths), it is described by its average composition — typically the alkyl chain range and the average number of ethylene oxide units.
What “N2EO” Means: Degree of Ethoxylation
The “N2EO” in the specification is the average number of ethylene oxide (EO) units per molecule. It is one of the most important variables in SLES because it controls solubility, mildness and performance.
| EO units (average) | Effect |
|---|---|
| 0 (this is SLS, not SLES) | Lauryl sulfate; more irritating, less soluble in hard water |
| 1–2 EO | Typical “SLES 2EO”; markedly milder than SLS, strong foaming |
| 3+ EO | More water-soluble and milder, often used where higher EO is wanted |
Adding EO units chains the sulfate head away from the hydrophobic tail through a hydrophilic spacer, which reduces the surfactant’s irritation potential on skin and eyes and improves its tolerance of hard water. This is why SLES is preferred over SLS in products that touch skin and eyes.
Physical and Chemical Properties
| Property | Typical value / behaviour |
|---|---|
| Appearance | White to yellowish paste (70% active) |
| Active matter | 70 ± 2% |
| Odour | Characteristic |
| pH (25 °C) | 7.0 – 10.0 |
| Colour (5% A.M.) | Hazen ≤ 20 |
| Sodium sulfate | ≤ 2.0% |
| Unsulfated matter | ≤ 3.0% |
| Ionic character | Anionic |
At 70% active, SLES is a paste rather than a liquid, which reflects its high concentration; it is supplied this way for economy and diluted to the use concentration in the finished product. The colour (measured as Hazen, a yellowness index) matters because SLES is used in clear and white personal-care products.
Surfactant Behaviour: Anionic, Foaming and Mildness
SLES is an anionic surfactant, meaning its hydrophilic head carries a negative charge. That charge gives it the properties that define a shampoo or cleaner:
- Detergency. The anionic head and hydrophobic tail together lift oils and soil from surfaces and hold them in the wash water.
- Foaming. SLES produces abundant, stable lather — the reason it dominates in shampoos and hand soaps, where foam signals cleaning to the consumer.
- Mildness. Because of the ethoxylate spacer, SLES irritates skin and eyes less than the non-ethoxylated SLS, which matters in products used daily and around the eyes.
- Compatibility. As an anionic surfactant, SLES is compatible with other anionics and with non-ionics, but is incompatible with cationic surfactants (such as the quaternary ammonium biocides), which form complexes with it.
The last point is a common formulation trap: an anionic surfactant such as SLES must not be combined with a cationic conditioner or biocide in the same phase, or both are neutralised.
Industrial Production: Ethoxylation and Sulfation
SLES is made in two main chemical steps, followed by neutralisation, with the feedstock being a fatty alcohol.
| Stage | Purpose | Notes |
|---|---|---|
| 1. Feedstock | Provide the fatty alcohol | Lauryl/myristyl alcohol (C12–C14), often from palm or coconut |
| 2. Ethoxylation | Add the EO units | Fatty alcohol + ethylene oxide over a catalyst gives the laureth (fatty alcohol ethoxylate) |
| 3. Sulfation | Install the sulfate group | Reaction with sulfur trioxide (SO3) or chlorosulfonic acid gives the alkyl ether sulfuric acid |
| 4. Neutralisation | Form the sodium salt | Neutralisation with sodium hydroxide gives sodium laureth sulfate |
| 5. Finishing and standardisation | Reach the 70% paste | Adjustment of active content, pH and colour; packaging |
Two production variables matter most for quality. The first is the degree of ethoxylation, which is controlled in the ethoxylation step and determines the N2EO figure and the mildness. The second is the 1,4-dioxane by-product: 1,4-dioxane can form during ethoxylation, and modern “low-dioxane” SLES is produced with process control (and sometimes a stripping step) to keep this impurity within customer and regulatory limits. A supplier’s ability to control dioxane is one of the clearest markers of process quality.
Specifications and Quality Control
SLES is controlled by active content, pH, colour, inorganic sulfate and unsulfated matter, with 1,4-dioxane as a critical impurity for many applications. A representative 70% specification is shown below.
| Parameter | Typical specification |
|---|---|
| Appearance | White to yellowish paste |
| Active matter | 70 ± 2% |
| Sodium sulfate | ≤ 2.0% |
| Unsulfated matter | ≤ 3.0% |
| pH (25 °C) | 7.0 – 10.0 |
| Colour (5% A.M.) | Hazen ≤ 20 |
| 1,4-Dioxane | Per customer/regulatory limit (low-dioxane grades available) |
Colour is a practical quality indicator: a low Hazen value (little yellow) is important for clear and white finished products. Sodium sulfate and unsulfated matter reflect the efficiency of the process and affect formulation and performance.
Grades, Forms and the 70% Paste
- 70% paste (2 EO). The standard commercial grade and the form described here.
- Other active contents. Lower percentages may be supplied for convenience in some systems.
- Higher-EO grades. More ethoxylated products for greater mildness and solubility.
- Low-1,4-dioxane grades. For cosmetic and personal-care uses where residual dioxane must be tightly controlled.
Applications: Shampoos and Personal Care
SLES is the primary cleansing surfactant in the majority of shampoos, body washes, shower gels, hand soaps and bubble baths. Its role is to clean and to foam, and it is usually formulated with co-surfactants (such as cocamidopropyl betaine, an amphoteric) to boost foam, improve mildness and thicken the product.
- Shampoos and body washes. Main surfactant; provides cleaning and rich lather.
- Hand soaps and shower gels. Gentle daily cleansing.
- Toothpaste. Provides foaming and helps disperse the paste during brushing.
- Facial cleansers. Where a milder sulfate is wanted than SLS.
Applications: Household and Industrial Cleaning
- Liquid dish and laundry detergents. SLES contributes cleaning power and foam, often blended with other surfactants.
- General-purpose and industrial cleaners. As a primary anionic surfactant in aqueous cleaning systems.
- Car wash and hard-surface cleaners. Foaming and soil removal.
- Bubble baths and foaming products. For its foam volume and stability.
SLES vs SLS and Other Sulfate Surfactants
SLES is often compared with SLS and with other anionic surfactants. The table summarises the key comparison.
| Surfactant | CAS | Type | Notes |
|---|---|---|---|
| SLES (sodium laureth sulfate) | 9004-82-4 | Alkyl ether sulfate (anionic) | Ethoxylated; milder, more soluble; shampoo standard |
| SLS (sodium lauryl sulfate) | 151-21-3 | Alkyl sulfate (anionic) | Not ethoxylated; stronger cleanser, more irritating |
| SLS + SLES blends | mixed | Anionic blend | Used to balance foam, mildness and cost |
The simplest way to remember the difference is that adding ethoxylation (SLES) makes a “kinder” molecule than the plain sulfate (SLS). A fuller comparison, and the role of anionic surfactants alongside amphoteric and non-ionic co-surfactants, is given in the related reading below.
Formulation and Handling Guidance
- Dilution and warming. The 70% paste is diluted to the use concentration; warm gently and mix, since it can thicken or set at low temperature.
- Co-surfactants. Pair with amphoteric and non-ionic surfactants (for example betaines and amine oxides) to boost foam, mildness and viscosity.
- Thickening. Salt (sodium chloride) is commonly used to thicken SLES-based shampoos; the response is non-linear and is optimised by trial.
- Cationic incompatibility. Never combine SLES with cationic surfactants or polymers in the same phase; they complex and lose activity.
- Preservation and pH. Finished products need preservation and pH control; SLES is stable across the usual personal-care pH range but can hydrolyse under strongly acidic conditions.
- Storage. Keep sealed, cool and out of direct sunlight; avoid contamination.
Safety, Health, Environment and Regulatory
- Irritancy. SLES is a mild-to-moderate skin and eye irritant, less so than SLS; concentrated product is more irritating. Handle with care and use PPE.
- 1,4-Dioxane. Because 1,4-dioxane is a possible by-product of ethoxylation, good SLES is specified for low dioxane, and the level must meet the customer’s and the market’s limits. This is the principal quality/regulatory issue for SLES.
- Biodegradability. SLES is readily biodegradable, which is one reason it has largely replaced less biodegradable surfactants in many applications.
- Regulatory. SLES is a permitted cosmetic and household surfactant in major markets; confirm the grade and documentation for the intended use, particularly for dioxane limits.
Market and Supply Overview
- Demand drivers. Global personal care and cleaning markets; SLES is a high-volume commodity surfactant.
- Production base. Made by many surfactant producers worldwide, with major capacity in Asia.
- Price drivers. The cost of fatty alcohol (palm/coconut-derived), ethylene oxide and energy.
- Quality differentiators. Active content, colour, dioxane level, sodium sulfate and unsulfated matter.
- Packaging. 200 kg drums and 1000 kg IBCs are typical.
Procurement and Sourcing Guide
- Active content and EO. Confirm the active matter and the ethoxylation (N2EO or as required).
- Colour. Specify a low Hazen value for clear and white products.
- 1,4-Dioxane. Require the dioxane level and confirm it meets your limit — critical for cosmetics.
- Inorganic sulfate and unsulfated matter. Check these for process quality.
- Documentation. Require the SDS, COA and any cosmetic/regulatory statements.
- Storage. Confirm packaging and cool, dark storage; warm and mix before use.
PolyBlueChem can supply SLES 70% (CAS 9004-82-4, also listed as 68585-34-2). To request current specifications, a COA or a quotation, contact the PolyBlueChem team.
Ethoxylation and Sulfation: The Chemistry in Detail
The two reactions at the heart of SLES manufacturing are worth understanding, because they explain both the product’s properties and its main quality risk.
| Reaction | What happens | Consequence |
|---|---|---|
| Ethoxylation | Fatty alcohol + ethylene oxide, ring-opening addition over a catalyst | Builds the –(OCH2CH2)n– spacer; sets mildness and solubility; a distribution of EO numbers results |
| Sulfation | The terminal hydroxyl of the ethoxylate reacts with SO3 | Installs the anionic sulfate head, making the molecule a surfactant |
| Neutralisation | The alkyl ether sulfuric acid is neutralised with NaOH | Gives the stable sodium salt (SLES) |
Ethoxylation is a statistical process: ethylene oxide adds one unit at a time, so the product is a mixture of molecules with different numbers of EO units, and the “2 EO” figure is an average. Producers control the average by the ratio of ethylene oxide to alcohol and by the catalyst and conditions. The ethoxylation step is also where 1,4-dioxane can form as a trace by-product, which is why the quality of the ethoxylation process — not just the sulfation — determines the purity of the SLES.
Building a Shampoo Base: Surfactant Blends
SLES is rarely used alone. A shampoo or body wash is a surfactant blend designed to balance cleaning, foam, mildness, viscosity and cost. The table shows the typical players.
| Component | Role | Typical chemistry |
|---|---|---|
| Primary anionic surfactant | Cleaning and foam | SLES (sodium laureth sulfate) |
| Secondary amphoteric | Mildness, foam boosting, viscosity | Cocamidopropyl betaine |
| Non-ionic | Mildness, foam, solubilisation | Alkyl polyglucosides, alcohol ethoxylates |
| Thickener / viscosity modifier | Body and rheology | Salt (NaCl), PEG distearates, gums |
| Conditioning agent | After-feel | Cationic polymers (added in a separate phase) |
| Preservative and pH adjuster | Stability and safety | Standard cosmetic preservatives and buffers |
The classic shampoo base pairs SLES with cocamidopropyl betaine: the betaine improves mildness and body and boosts the foam of the anionic surfactant. Note that cationic conditioning polymers (which carry a positive charge) must be handled so that they do not meet the anionic SLES in the same phase, or they complex and destroy the viscosity and clarity.
SLES, Hard Water and Cleaning Performance
One of SLES’s practical advantages over SLS is its behaviour in hard water. Because the ethoxylate spacer sits between the anionic sulfate head and the hydrophobic tail, the surfactant is less sensitive to calcium and magnesium ions than a plain alkyl sulfate.
- Hard-water tolerance. SLES remains effective and foams well in hard water, where plain soaps and some anionics fail.
- Lime-soap scum. SLES generates less of the insoluble “lime soap” precipitate, so it leaves less residue and feels less harsh.
- Foam in service. Good foam and cleaning in the presence of the water hardness typical of many markets make SLES a robust choice for consumer products worldwide.
- Formulation with chelants. Where water is very hard, small amounts of chelating agents further improve performance.
This combination of hard-water tolerance, mildness and foam is exactly why SLES displaced earlier surfactant systems and remains the reference anionic cleansing surfactant.
Handling, Storage and Stability
- Physical form. The 70% paste may set or thicken at low temperature; warm (typically to 30–40 °C) and mix before use or before transfer.
- Containers. Supplied in plastic drums or IBCs; keep sealed and use corrosion-resistant equipment.
- Stability. SLES is stable across normal storage and personal-care pH ranges, but hydrolyses under strongly acidic conditions; control pH in finished products.
- Contamination. Keep free of cationic materials and metal contamination, which can affect colour and performance.
- Storage conditions. Cool, dry and out of direct sunlight; rotate stock, especially of the paste, which can change consistency over long storage.
Why SLES: A Practical Summary
- Cleaning and foam. Strong anionic detergency with abundant, stable lather.
- Mildness. The ethoxylation makes it kinder to skin and eyes than SLS, so it suits frequent-use products.
- Hard-water tolerance. Effective across water hardness, with less lime-soap residue.
- Formulation flexibility and cost. Compatible with the common co-surfactants, easy to thicken with salt, and economical at scale.
- Biodegradability. Readily biodegradable, supporting its continued dominance in consumer cleaning.
The main things to manage are the cationic incompatibility and the 1,4-dioxane impurity, both of which are addressed through formulation design and supplier specification respectively.
Sustainability and the Surfactant Landscape
SLES sits in a surfactant market that is under growing pressure to become more sustainable, and this shapes both its competitive position and the way buyers think about it.
- Readily biodegradable. SLES biodegrades readily, which is a core reason it displaced older, more persistent surfactants.
- Bio-based feedstock. Its fatty alcohol comes from palm or coconut oil, so a large part of the molecule is renewable; buyers increasingly ask about the feedstock’s sustainability certification.
- Competition from milder and “sulfate-free” systems. A consumer trend toward “sulfate-free” and “gentle” claims has increased interest in alternative surfactants (glucosides, isethionates, amino-acid surfactants), even though SLES remains the volume standard.
- Impurity focus. The industry’s focus on low 1,4-dioxane has made impurity control a competitive and regulatory differentiator.
For a buyer, the practical takeaway is that SLES remains the cost-effective, high-performance cleansing workhorse, but demand is increasingly segmented: mainstream cleaning and personal care continue to use it at scale, while premium “sulfate-free” positioning drives the alternatives. Choosing between them is a marketing and formulation decision as much as a technical one.
Frequently Asked Questions
What is SLES and what is its CAS number?
SLES is sodium laureth sulfate (sodium lauryl ether sulfate), an anionic surfactant; it is commonly listed as CAS 9004-82-4 (also 68585-34-2). See the product page for specifications.
What does N2EO mean?
It is the average degree of ethoxylation — about 2 ethylene oxide units per molecule in this grade — which affects mildness and solubility.
Is SLES the same as SLS?
No. SLES is ethoxylated (CAS 9004-82-4); SLS is not (CAS 151-21-3). SLES is generally milder and more soluble.
What is SLES used for?
Mainly shampoo, body wash, hand soap and other personal-care cleansing products, plus liquid detergents and cleaners.
Why is 1,4-dioxane important for SLES?
Because it can form during ethoxylation and is a controlled impurity; low-dioxane SLES is specified for cosmetics and other sensitive uses.
Can SLES be mixed with cationic ingredients?
No, not in the same phase. As an anionic surfactant, SLES complexes with cationic surfactants and polymers, and both lose activity.
How is SLES made?
By ethoxylating a fatty alcohol and then sulfating and neutralising it — fatty alcohol + ethylene oxide gives the laureth, which is sulfated with SO3 and neutralised with sodium hydroxide.
How should SLES be stored?
Sealed, cool and out of direct sunlight; the 70% paste may thicken in the cold, so warm and mix before use.
What is the difference between 2EO and 3EO SLES?
The number is the average ethylene oxide units per molecule. More EO makes the surfactant more water-soluble and milder; 2EO is the common shampoo grade.
Is SLES biodegradable?
Yes, SLES is readily biodegradable, which is one reason it became the dominant anionic cleansing surfactant.
Is SLES derived from palm oil?
Its fatty alcohol feedstock is commonly derived from palm or coconut oil, so a substantial part of the molecule is renewable; buyers increasingly ask about the feedstock’s sustainability certification.
References and Disclaimer
References. Substance identification data for sodium laureth sulfate (CAS 9004-82-4 / 68585-34-2); standard chemistry of alkyl ether sulfate surfactants and their manufacture by ethoxylation and sulfation; manufacturer technical data for the 70% grade. Specifications quoted are representative and should be confirmed against the current certificate of analysis.
Disclaimer. This article is provided for general technical and commercial information only and does not constitute a specification or a warranty of fitness for any particular use. Users are responsible for confirming regulatory status, safe handling and suitability of the material for their own application and market.