Ascorbic Acid

Ascorbic acid (L-ascorbic acid) is a potent antioxidant/brightening active typically used around 5–20% and requires a low, acidic pH (~2.5–3.5) for stability and efficacy, which commonly causes stinging, burning, and erythema—especially on compromised barriers (eczema, rosacea, post-procedure). Clinical experience and patch/usage testing show higher irritation rates at typical effective concentrations and with repeated use in multi-active routines, so careful introduction and buffering are often needed for sensitive skin. Safety Notes: In real-world OTC skincare, ascorbic acid appears at very low levels (~0.01–0.1%) in multi-ingredient creams/lotions and some rinse-off cleansers where it is more of a supporting antioxidant than a primary active. Most leave-on serums and treatment products cluster around ~5–20% (consistent with published topical-use studies and common industry practice), while a smaller set of consumer-available “high-strength” water-based, anhydrous, or powder-to-serum products reach ~25–30% (typically requiring low pH and/or specialized packaging due to instability and irritation risk).