Hydroxypropyl Starch Phosphate

Hydroxypropyl starch phosphate is a modified starch used primarily as a thickener/texture enhancer and oil-absorbing agent, typically at low single-digit percentages, and it is generally considered non-reactive with a low rate of irritation in patch testing for leave-on products. In very compromised skin it can rarely contribute to dryness/tightness (especially in mattifying formulas), so I do not score it as fully inert, but overall it remains very gentle for most sensitive-skin patients. Safety Notes: In commercial leave-on skincare and color cosmetics, hydroxypropyl starch phosphate is commonly used at very low levels (~0.05–0.5%) as a rheology modifier, stabilizer, and sensory/blur agent in emulsions and gels. Mid-range usage (1–5%) is widely seen in mattifying lotions/primers and powdery-feel creams where a stronger oil-absorbing and slip effect is desired. High-strength consumer products such as oil-control primers, blurring balms, and some sunscreen/BB-type bases can reach ~8–10%, with higher levels limited by texture (dryness/drag, pilling) and viscosity/dispersion constraints rather than specific regulatory caps.