Illite

Illite is a mineral clay (often used in masks/cleansers at high percentages) that functions mainly as an absorbent and viscosity/bulking agent. While not a classic chemical irritant, clays can cause dryness, tightness, and barrier disruption—especially in eczema-prone or compromised skin—leading to stinging and reactive dermatitis in real-world use. Patch testing generally shows low reactivity, but given typical use concentrations and the risk of over-drying in sensitive populations, it fits best as a gentle (not exceptionally gentle) ingredient. Safety Notes: Illite (a mineral clay, often listed as Illite/Yellow Clay/French clay) appears at very low levels (~0.1–1%) in emulsions and cleansers as an opacity/skin-feel modifier or mild oil-absorbing aid, and at moderate levels (~2–20%) in wash-off masks and scrubs for absorbency and texture. The highest consumer-available concentrations are found in powder masks and clay pastes where illite is a primary solid phase (commonly ~40–70% and up to ~80% when blended with minimal other powders/binders); these are typically rinse-off products, while leave-on products rarely exceed a few percent due to grit, color, and wearability.