C E Ferulic

The reference formula

L-ascorbic acid is vitamin C in its pure, most-studied form, and this is the formula that showed the industry how to keep it potent: an acidic, water-based serum in which 0.5% ferulic acid stabilises 15% vitamin C and 1% alpha-tocopherol, each extending the others' working life. The nine-line ingredient list has barely changed in two decades because it has not needed to.

What it does by day

Applied each morning it becomes the antioxidant layer under sunscreen: SPF blocks what it can, the vitamin C network deals with the environmental stress that gets through. With consistent use skin looks brighter and firmer, and tone more even.

The benchmark

This is one of skincare's few genuinely reference products, the serum other vitamin C formulas are measured against, and the reason a nine-ingredient bottle carries a clinical library most brands cannot match.

Normal, dry and combination skin from the first signs of ageing onward; city skin wanting a serious daily antioxidant shield under SPF; and anyone who has worked through lesser vitamin C serums and wants the benchmark.

Worth knowing

Pure L-ascorbic acid at this strength can tingle for the first week or two, a sign of the low pH doing its job rather than a fault. Fragrance-free; the formula's faint savoury scent is characteristic and fades on skin within minutes.

Mornings after cleansing: four to five drops pressed over dry face, neck and chest, then moisturiser and SPF once it settles.

Sensitive skin can begin every other morning and build to daily as the tingle fades.

Use alongside

Built for mornings under SPF, Melan 130 where pigmentation is part of the picture. Retinoids keep to the evening shift, Crystal Retinal being a natural partner, so the two never compete. Leave same-morning exfoliating acids out; the serum's own low pH is acid enough.