What it is
This ingredient is the ester formed between stearic acid and polyethylene glycol with about 40 ethylene-oxide units, making it a water-soluble nonionic surfactant. In sunscreens and moisturizers it serves mainly as an oil-in-water emulsifier, keeping the oil and water phases blended into a stable, uniform emulsion. It also contributes to a softer, more spreadable texture.
Safety & warnings
PEG fatty-acid esters are common, well-established emulsifiers with a good tolerability record. Being ethoxylated, they require supplier purification to keep residual ethylene oxide and 1,4-dioxane low. It is generally considered low in irritation and sensitization potential and is not regarded as notably comedogenic at typical use levels.
Origin & sourcing
Semi-synthetic; made from stearic acid, a fatty acid that can be of plant or animal origin, esterified with polyethylene glycol.
Questions everyone asks
What does PEG-40 Stearate do in a formula?
It works as a nonionic oil-in-water emulsifier, helping keep the oil and water phases blended into a smooth, stable cream or lotion.
Is PEG-40 Stearate vegan?
It depends on the source of the stearic acid, which can be plant- or animal-derived; that varies by supplier and is not determined by the INCI name alone.