Sodium Dodecyl Sulfate (SLS) — Frequently Asked Questions

SLS (sodium lauryl sulphate) is made by sulphating lauryl alcohol directly. SLES (sodium laureth sulphate) is made from lauryl alcohol that has first been ethoxylated, which adds a short chain of ethylene oxide units. SLES is milder, more soluble and easier to thicken with salt, so it dominates liquid shampoos and body washes. SLS foams very strongly and is supplied as a solid, so it is standard in toothpaste, powders and many cleaners.

Needles give high active content with less dust and better flow, which suits most solid-dosing plants. Powder dissolves fastest and blends well into dry products such as toothpaste bases and powdered cleaners, but it is dusty. Liquid at around 28–30% active avoids dust altogether and is easy to pump, but you pay to ship water and need warm storage. Choose the form that suits your plant and your product.

SLS can irritate skin at high concentrations and with long contact, which is why it is used as a reference irritant in dermatology testing. In rinse-off products at normal levels, especially when combined with amphoteric surfactants such as betaines or with non-ionic surfactants, irritation is much lower. Many formulations use SLS successfully, while others use SLES or milder surfactants for sensitive-skin or leave-on claims. Test the finished product.

Unsulphated matter is mostly fatty alcohol that did not react during sulphation, with small amounts of other oily by-products. Higher levels reduce clarity in solutions, can affect foam and odour, and show a less complete reaction. Specifications usually set a maximum, typically around 1.5% for needles and powder. Together with sodium sulphate and sodium chloride, it tells you how clean the product is.

Sodium dodecyl sulphate has a Krafft point, the temperature below which it crystallises out of water, of roughly 15–20 °C depending on purity. Below that, liquid SLS becomes hazy, thick or solid. The product is not damaged. Warm it gently to above about 25 °C and mix it before use. Keep liquid grades in heated or indoor storage, and specify heated tanks for bulk.

It is the same molecule, sodium dodecyl sulphate, but not the same product. Laboratory and electrophoresis grades are high-purity C12 with tight limits on other chain lengths and impurities, because those affect analytical results. Industrial and personal-care SLS is usually a C12-rich blend with some C14, specified for foaming and cleaning performance. Buy laboratory grades from a laboratory specification. The bulk grades on this page are for manufacturing.