Collection: Obagi Vitamin C Serums

For most skin types, 15% is the ideal starting point — it delivers a clinically effective concentration without excessive irritation. If your skin is sensitive or you have never used active skincare, start at 10%. After 2–3 months at 15% with good tolerance, you can step up to 20% for maximum antioxidant protection. There is limited clinical benefit above 20%, so the Professional-C 20% represents the ceiling of what is useful in a topical serum.

Yes, but not in the same routine. Vitamin C works best at a low pH (around 2.5–3.5), while retinoids perform optimally at a slightly higher pH. Applying them together can reduce the efficacy of both. The best approach is vitamin C in the morning and your retinoid (Crystal Retinal, retinol, or Advanced-Protocol Retinoid) in the evening. This way each active works at its optimal pH, and you get comprehensive daytime antioxidant protection plus overnight cell renewal.

L-ascorbic acid is inherently unstable and oxidises when exposed to air, light, and heat. If your serum has turned from clear or pale gold to a deep orange or brown, it has oxidised significantly and should be replaced. To extend shelf life, store your Obagi Professional-C in a cool, dark place (a bathroom cabinet is fine), keep the cap tightly sealed, and use it within 3 months of opening. A slight deepening in colour is normal over time, but a dramatic change indicates reduced efficacy.

Both are excellent clinical-grade vitamin C products, but they take different approaches. Obagi uses pure L-ascorbic acid at a low pH for maximum potency and penetration — ideal for those who want the strongest direct antioxidant hit. Medik8's C-Tetra range uses tetrahexyldecyl ascorbate, a lipid-soluble vitamin C derivative that is gentler and more stable but requires conversion in the skin. If your skin tolerates acids well, Obagi's L-ascorbic acid formulation is the more potent choice. If you have sensitive skin or find acids irritating, Medik8 may suit you better.

Yes — SPF and vitamin C protect against UV damage through completely different mechanisms. Sunscreen filters and reflects UV radiation before it hits your skin, while vitamin C neutralises the free radicals that are generated by UV exposure that does get through. No sunscreen blocks 100% of UV, and free radical generation continues even after sun exposure ends. Using both together provides significantly greater photoprotection than either alone. Think of SPF as your shield and vitamin C as your repair crew. This combination is especially important if you are treating pigmentation or uneven tone.