Sodium Laureth-13 Carboxylate

An ether carboxylate surfactant, made by attaching a carboxylic acid group to an ethoxylated fatty alcohol. The 13 refers to the degree of ethoxylation. It is used as a cleansing and foaming agent, and belongs to a class of surfactants generally regarded as milder than sulfates while still producing decent lather.

Like all cleansing surfactants it works by surrounding oil and grime so they can be rinsed away with water. The useful property here is that its charge depends on pH. It is fully anionic in neutral and alkaline conditions, and as a cleanser is formulated more acidic a growing fraction converts to the uncharged acid form, which interacts less aggressively with skin proteins than a permanently charged surfactant such as sodium lauryl sulfate. That is the mechanism behind its milder reputation, and it is why the pH a cleanser is formulated at matters as much as which surfactant it contains.