What is it?
A cleansing agent made by joining lauric acid, a fatty acid abundant in coconut oil, to a methyl form of isethionic acid and forming the sodium salt. It foams and helps water rinse away oil and dirt, and it is used mainly in shampoos, body washes and other rinse-off cleansers. It is a close relative of sodium cocoyl isethionate, a cleanser used in syndet (synthetic detergent) bars.
Key information
- The CIR Expert Panel concluded in 2013 that sodium lauroyl methyl isethionate and 11 related isethionates are safe as used when formulated to be non-irritating.
- It is a sulfonate, not a sulfate, and it is not sodium lauryl sulfate.
- In 2013 it was reported only in rinse-off products, at up to about 10 percent.
More information
Isethionates share a core called isethionic acid (2-hydroxyethanesulfonic acid), which has an alcohol group at one end and a sulfonic acid group at the other. Joining a fatty acid to the alcohol end gives a surfactant with an oil-loving tail and a water-loving sulfonate head. In sodium lauroyl methyl isethionate, the fatty acid is lauric acid and the core carries an extra methyl group. The Cosmetic Ingredient Review (CIR) reported 33 uses in 2013, all rinse-off and more than half in hair products, at 0.64 to 10.1 percent.
The CIR Expert Panel reviewed it with 11 other isethionate salts. There were no test data on sodium lauroyl methyl isethionate itself, so the Panel relied on data for the group, mainly sodium cocoyl isethionate. It noted little or no irritation or allergy in many skin and eye tests and no genetic damage in laboratory tests. It also noted that most surfactants cause some irritation: in human studies, sodium cocoyl isethionate irritated less than sodium lauryl sulfate, though in one comparison of eight surfactants it was the second most irritating after it. The Panel concluded that isethionates are safe as used when formulated to be non-irritating.
Reality check: the names look alike, but this is not sodium lauryl sulfate (SLS). SLS is a sulfate, which the CIR describes as an irritant in patch tests at 2 percent and above and limits to 1 percent in leave-on products. Sodium lauroyl methyl isethionate is a sulfonate ester, and its name has none of the markers the FDA links to 1,4-dioxane. On labels, look for “methyl isethionate”; “lauryl sulfate” and “laureth sulfate” are the ingredients the Foundation rates Red Light.
Sources: Cosmetic Ingredient Review: Amended safety assessment of isethionate salts (2013); Cosmetic Ingredient Review: Sodium lauryl sulfate and sodium laureth sulfate safety summary; FDA: 1,4-Dioxane in cosmetics, a manufacturing byproduct
