What is vitamin C in skincare?
L-Ascorbic acid is the pure, active form of vitamin C in skincare. It is water-soluble, and its instability — it oxidises quickly when exposed to air and light — is what separates a high-quality vitamin C serum from a marketing product. A serum that has turned orange or yellow has oxidised and lost most of its potency. This is why SkinCeuticals C E Ferulic, which stabilises L-ascorbic acid with vitamin E and ferulic acid, is considered the benchmark vitamin C formulation.
Other forms include ascorbyl glucoside, sodium ascorbyl phosphate, and tetrahexyldecyl ascorbate — these are more stable but require conversion to L-ascorbic acid in the skin, making them less potent and slower-acting. For maximum results, choose a formulation with stabilised L-ascorbic acid at 10–20%.
What vitamin C does for skin
Vitamin C works through three distinct mechanisms. First, as an antioxidant: it neutralises free radicals generated by UV radiation, pollution, and metabolic processes before they can damage DNA, collagen, and cell membranes. Applied before sun exposure, it provides a layer of protection that SPF alone cannot offer.
Second, it inhibits tyrosinase — the enzyme responsible for melanin production — reducing the formation of new dark spots and gradually fading existing hyperpigmentation. This makes it particularly valuable for treating UV-induced pigmentation and uneven skin tone.
Third, vitamin C is directly involved in collagen synthesis. It is a required cofactor for the enzymes that stabilise and crosslink collagen fibres. Without adequate vitamin C, the collagen produced by fibroblasts is structurally weaker and less durable.
Choosing the right vitamin C for your skin
SkinCeuticals C E Ferulic (15% L-ascorbic acid) is formulated for normal, dry, and sensitive skin. SkinCeuticals Phloretin CF is formulated for oily and combination skin, with a lighter texture and the addition of phloretin — a potent polyphenol that enhances antioxidant protection. Both are backed by published clinical research.
For Fitzpatrick Type IV–VI skin (olive to very dark), vitamin C is a safe and effective brightening ingredient. It does not cause paradoxical darkening. However, pair it with a Heliocare 360° Pigment Solution SPF — both ingredients work synergistically and visible light (not just UV) triggers melanin production in darker skin tones independently of UVA/UVB.