L-Ascorbic Acid Stability: Why Your Vitamin C Serum Keeps Turning Orange

By Michael C. · Written and reviewed by Michael C.

Vitamin C · Published 2026-07-22 · 10 min read · 1980 words · Updated 2026-09-08

L-ascorbic acid is the most potent form of vitamin C, but it oxidises easily, so packaging and storage matter as much as concentration.

Key takeaways

• L-ascorbic acid is the most researched form of vitamin C but oxidises easily with light, air and heat exposure.
• Effective concentrations generally sit between 10 and 20 percent at a low pH of around 3.5.
• A serum that has darkened to amber, brown or orange has likely lost much of its potency.
• Opaque, airless packaging and cool, dark storage meaningfully extend a product's usable life.

Source: SkinLabs Editorial Team ()

Cover image: Viva Luna Studios — credit