Oleth-20 is a synthetic polymer composed of oleyl alcohol and polyethylene glycol. The number associated with the ingredient name (i.e., oleth-20) corresponds to the number of repeat units of ethylene glycol. In cosmetics and personal care products, oleth-20 functions as a surfactant and emulsifier.
Oleth-20 is used as a surfactant in many different cleansers, body washes, and hair care products. It lowers the surface tension between two immiscible substances because its structure contains one end that is hydrophilic (attracted to water) and one end that is lipophilic (attracted to oil). This structure allows oleth-20 to attract and suspends oils, dirt, and other impurities that have accumulated on the skin and wash them away.
Oleth-20 can also be used as an emulsifier in formulations that contain both water and oil components. Mixing water and oil together creates a dispersion of oil droplets in water (and vice versa). These two phases can separate if the product is left to settle. To address this problem, an emulsifier can be added to help the droplets remain dispersed. With an HLB value of 15.3 oleth-20 is soluble in water and gives rise to oil-in-water emulsions.