Versatile ingredient composed of several non-volatile alcohols. Functions primarily as a surfactant, but can also be used as a skin-conditioning agent, emulsifier, and solvent. Sodium lauryl sulfate (SLS) is one of the most irritating cleansing agents used in skincare products. In fact, it’s considered a standard comparison substance for measuring the skin irritancy of other ingredients. Thus, in scientific studies, when they want to establish whether or not an ingredient is problematic for skin, they compare its effect to the effect of SLS. 
In amounts of 2% to 5%, sodium lauryl sulfate can cause allergic or sensitizing reactions for many people. [2,3] Despite the irritancy issue, it is not the same as the dire and erroneous warnings floating around the web about this ingredient.
- Robinson V, Bergfeld W, Belsito D, Hill R, Klaassen C, Marks JJ, Shank R, Slaga T, Snyder P, Andersen A. Final report of the amended safety assessment of sodium laureth sulfate and related salts of sulfated ethoxylated alcohols. Int J Toxicol. 2010;29(4S):151S-61S.
- Löffler H, Pirker C, Aramaki J, Frosch P, Happle R, I. E. Evaluation of skin susceptibility to irritancy by routine patch testing with sodium lauryl sulfate. Eur J Dermatol. 2001;11(5):416-9.
- Löffler H, Freyschmidt-Paul P, Effendy I, Maibach H. Pitfalls of irritant patch testing using different test chamber sizes. Am J Contact Dermat. 2001;12(1):28-32.
sodium laureth sulfate