Sodium Laureth Sulfate in Shampoos and Personal Care
Sodium laureth sulfate (SLES) is the surfactant most people meet every day, because it is the primary cleanser in the majority of shampoos, body washes, hand soaps and shower gels. Its job is to clean and to foam, gently enough for daily use on skin and hair. This article explains why SLES was chosen for that role, how it is used in personal-care formulas, and how it compares with the alternatives.
For the full product background, see our main article on sodium laureth sulfate (SLES, CAS 9004-82-4).
Why SLES Is the Personal-Care Workhorse
Three properties made SLES the dominant cleansing surfactant in personal care:
- Cleaning power. As an anionic surfactant it lifts oils, sebum and soil and holds them in the wash water.
- Foam. It produces abundant, stable lather, which consumers read as effective cleaning.
- Mildness. The ethoxylate spacer makes it gentler on skin and eyes than the non-ethoxylated SLS, which matters for products used daily and near the eyes.
Add hard-water tolerance and low cost, and SLES becomes the obvious volume choice — which is why it appears so widely despite the rise of “sulfate-free” marketing.
SLES in a Shampoo Formula
SLES almost never works alone; it is the “primary” surfactant in a blend. The table below shows the typical structure of a shampoo or body wash.
| Ingredient class | Example | Contribution |
|---|---|---|
| Primary anionic surfactant | SLES | Cleaning and foam |
| Secondary amphoteric | Cocamidopropyl betaine | Mildness, foam boost, viscosity |
| Non-ionic | Alkyl glucoside | Mildness, foam, solubilisation |
| Thickener | Sodium chloride, PEG distearate | Product body and flow |
| Conditioning polymer | Cationic guar or PQ-10 | Softness, after-feel (separate phase) |
| Preservative, pH adjuster, actives | Various | Safety, stability, claims |
The betaine is the classic partner for SLES: it makes the product milder, boosts the foam and helps build viscosity. Cationic conditioning polymers, which carry a positive charge, must be kept out of the same phase as the anionic SLES or they will complex and destroy the viscosity and clarity of the product.
Mildness and the SLS Question
Consumers often hear that “sulfates” are harsh, but not all sulfates are equal. SLES and SLS differ in one crucial respect: ethoxylation.
| Surfactant | CAS | Mildness | Typical use |
|---|---|---|---|
| SLES (sodium laureth sulfate) | 9004-82-4 | Milder (ethoxylated) | Shampoo, body wash, daily cleansers |
| SLS (sodium lauryl sulfate) | 151-21-3 | More irritating (not ethoxylated) | Stronger cleansing, toothpaste, some cleaners |
| SLMI (sodium lauroyl methyl isethionate) | — | Very mild (sulfate-free) | Premium “gentle” / sulfate-free products |
Because SLES is milder than SLS, it suits the daily-use products where SLS would be too harsh. Where a brand wants a “sulfate-free” claim, it turns to alternatives such as isethionates and glucosides — see the related reading for a comparison of gentle surfactants.
Formulation Tips for SLES Cleansers
- Dilution and warming. Warm the 70% paste gently (about 30–40 °C) and dilute to the use concentration before adding other ingredients.
- Order of addition. Add the anionic and amphoteric surfactants first, then thickeners, then heat-sensitive actives and preservatives.
- Salt thickening. Sodium chloride thickens SLES-based formulas, but the response is non-linear; find the optimum by trial.
- Cationic phase separation. Keep conditioning polymers and cationic actives in a separate phase or use compatible (non-complexing) systems.
- pH and preservation. Target the skin-friendly pH range and use an adequate preservative system.
Sustainability and the “Sulfate-Free” Trend
SLES is readily biodegradable and based partly on renewable fatty alcohol, but a consumer preference for “sulfate-free” and “gentle” claims has led brands to offer alternatives. The practical reality is a segmented market: SLES remains the cost-effective, high-performance cleanser for the mainstream, while sulfate-free systems serve premium and sensitive-skin positioning. A formulator chooses per product brief, not per ideology.
Frequently Asked Questions
Why is SLES used in shampoo?
Because it cleans strongly, foams well, is milder than SLS, tolerates hard water and is economical — the combination a shampoo needs.
Is SLES bad for hair or skin?
SLES is a mild-to-moderate irritant, less so than SLS, and is used in countless daily products. Sensitive users may prefer sulfate-free systems.
What is SLES usually combined with?
Most often cocamidopropyl betaine, with non-ionic co-surfactants, salt for thickening and a preservative system; conditioning polymers go in a separate phase.
Is SLES sulfate-free?
No. SLES is a sulfate surfactant; “sulfate-free” products use other chemistries such as isethionates or glucosides.
How do I thicken an SLES shampoo?
Salt (sodium chloride) is the usual thickener, with PEG distearates or gums as alternatives; the amount is optimised by trial.