Polyglyceryl-4 Isostearate

Polyglyceryl-4 isostearate is a non-ionic emulsifier/surfactant typically used at low concentrations (about 0.5–5%) to stabilize water-in-oil systems, and it is generally well tolerated in patch testing and clinical use. While it lacks the protein-reactive or acid/base activity seen in higher-irritancy actives, any surfactant/emulsifier can provoke stinging or barrier-related irritation in a minority of highly reactive or eczematous patients, especially in compromised skin. Given its overall favorable safety profile but non-zero risk in severely sensitive populations, it fits a very gentle score rather than inert. Safety Notes: Polyglyceryl-4 Isostearate is used primarily as a W/O emulsifier and pigment wetting/dispersing agent, so it shows up at very low levels (~0.1–0.5%) in conventional leave-on lotions/creams where it functions as a secondary co-emulsifier or stabilizer. In higher-oil, W/O systems (water-in-oil foundations, tinted sunscreens, balm-like creams, and anhydrous makeup cleansing oils/balms), commercial products commonly use it around 2–10%, and high-strength consumer formulations can reach ~15–20% when it is a primary structuring/emulsifying component. Rinse-off products typically sit toward the lower-middle of the range (often ~0.5–5%) unless they are oil-heavy cleansing balms designed to self-emulsify on contact with water.