Tbhq

TBHQ (tert-butylhydroquinone) is an antioxidant preservative typically used at very low concentrations (commonly up to ~0.02% in foods; similarly low when used in lipid phases), so it is not a primary irritant for most users. However, as a substituted hydroquinone derivative, it has documented potential for irritant and occasional allergic contact dermatitis in susceptible individuals on repeated exposure. Given low typical use levels but non-zero sensitization risk—especially in eczema-prone skin—I rate it as generally well-tolerated yet not inert. Safety Notes: TBHQ (tert-butylhydroquinone) is an antioxidant primarily used to stabilize oxidation-prone oils/fragrance components; in consumer cosmetics it is typically present at trace levels around 0.0005–0.02% in emulsions, anhydrous oils, and sunscreens where it functions as an oxidative stabilizer rather than an active. The upper end (up to ~0.10%) reflects high-antioxidant stabilization approaches seen in some specialty/high-oil anhydrous products and is aligned with common industry limits used for cosmetic antioxidants (often kept at or below ~0.1%) to balance efficacy, odor/color stability, and irritation/sensitization risk; it is generally similar for leave-on vs rinse-off because it is used for formula protection.