Sodium Lauryl Sulfate

Sodium lauryl sulfate is a cleansing surfactant. The European CosIng database assigns it four functions: cleansing, denaturant, foaming and surfactant cleansing. It does not appear among prohibited or restricted substances in the annexes to Regulation (EC) 1223/2009. OECD Test Guideline 439, which measures skin irritation in vitro, suggests a 5% aqueous solution as a positive control: a benchmark for comparison.

That final sentence needs explanation: it says something specific about the measurement method, yet is often read as a judgement on the molecule.

The function concerned with taste

Definitions of these codes were published in the Official Journal in 2006 within the European cosmetic ingredient inventory. CLEANSING helps keep the body surface clean; FOAMING traps small air bubbles in a liquid by changing its surface tension; SURFACTANT, which CosIng now specifies as surfactant – cleansing, lowers that tension and helps distribute the product evenly.

The remaining function is DENATURANT, defined in the same text as making cosmetics unpleasant to taste, particularly products containing ethyl alcohol. That role concerns the product's taste. Sodium laureth sulfate's function list has emulsifying in place of this entry.

Why it is used as a benchmark

CosIng also gives a chemical name: Sodium dodecyl sulphate. The same name, with CAS number 151-21-3, appears in the inventory dated 5 April 2006. In laboratory literature, the molecule is known by this name, abbreviated SDS.

Article 18 of Regulation (EC) 1223/2009 prohibits marketing cosmetics whose ingredients have undergone animal testing once an alternative method has been validated and adopted at Community level, taking OECD validation developments into account. For skin irritation, that method is described in OECD Test Guideline 439, adopted on 25 June 2025: it applies the test substance to reconstructed human epidermis and measures how many cells remain viable.

Paragraph 24 requires each run to include negative and positive controls: it suggests a 5% aqueous SDS solution as the positive control and water or phosphate-buffered saline as the negative. The glossary defines the positive control as a sample treated with a substance known to produce a positive response, while paragraph 34 requires the tissues to demonstrate responsiveness to an irritant under the method's conditions. Paragraphs 17 and 19 also cite the molecule as a reference substance for checking whether the stratum corneum resists rapid penetration.

The glossary adds a condition: the magnitude of the positive-control response must remain within a range that allows variation over time to be assessed. The molecule's assigned role is therefore to calibrate the test system.

Concentration, time and rinsing

The guideline's figures apply together with their conditions: 5% in water, direct application to reconstructed epidermis, exposure for 15–60 minutes, washing with aqueous buffer or 0.9% saline, then 42 hours of incubation before measurement. The guideline explains that times and temperatures are optimised for each epidermal model.

A finished product requires a different assessment. In its 1983 final report, Cosmetic Ingredient Review, the US expert panel reviewing cosmetic ingredients for that market, concluded that sodium lauryl sulfate and ammonium lauryl sulfate were safe in formulations designed for brief, discontinuous use followed by thorough rinsing, and that concentrations should not exceed 1% for prolonged skin contact. The panel's September 2020 reference table still reports that conclusion.

There are three variables: how much, for how long and with what rinsing. Irritation data without all three describe a laboratory condition, rather than how a cleanser will behave in everyday use. How well your skin tolerates a cleanser needs to be assessed one product at a time.

The two records, field by field

CosIng gives the entries different chemical names: Sodium dodecyl sulphate for this ingredient and sodium 2-(2-dodecyloxyethoxy)ethyl sulphate for sodium laureth sulfate. Sodium lauryl sulfate also has a European Pharmacopoeia name, natrii laurilsulfas, and an international non-proprietary name. Those two fields are blank for the other entry.

The significance of the three letters 'eth' is explained on the sodium laureth sulfate page.

Where to find it on the label

It appears as Sodium Lauryl Sulfate in products designed to cleanse. List order reflects quantity only above 1%; below that threshold, it remains flexible. The label does not give the exact percentage, which is particularly relevant here.

The threshold is explained fully in how to read an INCI list. If you have a label in front of you, the INCI analyser explains it ingredient by ingredient.

Sources: CosIng, European Commission, Sodium Lauryl Sulfate and Sodium Laureth Sulfate entries. Decision 2006/257/EC of 9 February 2006, OJ L 97 of 5 April 2006, amending Decision 96/335/EC, repealed by Decision (EU) 2019/701 from 8 May 2020. Regulation (EC) 1223/2009, Article 18. OECD, Test Guideline No. 439, In Vitro Skin Irritation: Reconstructed Human Epidermis Test Methods, 25 June 2025. Cosmetic Ingredient Review, Final Report on the Safety Assessment of Sodium Lauryl Sulfate and Ammonium Lauryl Sulfate, JACT 2(7):127-181, 1983.