For centuries, sailors dreaded scurvy without knowing its cause.

It wasn't until 1747 that a Scottish physician, James Lind, proved that citrus fruits cured the disease, and 1932 before the molecule responsible was isolated by Hungarian researcher Albert Szent-Györgyi, who won the Nobel Prize five years later. Its name, "ascorbic acid," literally means "against scurvy."

Unlike most mammals, our bodies can't manufacture it. We have to source it every day from our diet... and, to give our skin the best of it, apply it directly.

In the body, vitamin C is everywhere. It helps build collagen, the protein that gives skin, bones and blood vessels their strength. It supports immune defenses, improves the absorption of plant-based iron, and neutralizes free radicals generated by stress, fatigue or pollution¹.

Because it's water-soluble, it isn't stored: any excess is eliminated, which is why a regular intake matters. An orange, a kiwi and a handful of black currants easily cover a typical daily need. It's fragile and doesn't like prolonged cooking: favor raw or lightly cooked fruit and vegetables.

Not all vitamin C is equal. The pure form, ascorbic acid, is unstable in light, heat and water; it penetrates poorly and can be harsh on skin^1,5. That's why cosmetic science developed stabilized derivatives, whose efficacy varies by form⁵. Here are the ones we've chosen, and which products you'll find them in.

• Concentrated serums (10–20%): the fast track to visible glow and dark spot results;
• Day creams with antioxidant and anti-pollution action;
• Firming treatments (serums and firming creams);
• Glow creams with citrus;
• Men's care for an energizing boost;
• Sun and after-sun care, as antioxidant protection for oils.

1. In the morning, on cleansed skin
   Mist with Yon-Ka Lotion, then apply the vitamin C treatment that fits your ritual — concentrated serum, antioxidant cream or glow cream — over your face and neck.
2. Seal and protect
   Follow with your day cream, then sun protection: the vitamin C + SPF duo is the most effective combination against premature aging.
3. At night, alternating
   Use your vitamin C treatment alone or alternate it with a renewing active (fruit acids, retinol-like), rather than layering them at the same time.
4. Sensitive skin?
   Start with one application every other night, then gradually increase based on your skin's tolerance.

Reminder: vitamin C, in one form or another, is part of a large share of our treatments — not just one dedicated serum.

Pure vitamin C is a living active ingredient: it oxidizes with air and light, and a formula that turns noticeably dark orange has lost potency. Esterified forms like ascorbyl tetraisopalmitate are far more stable⁴. In every case, keep your bottle tightly closed, away from light, heat and humidity, and follow the period-after-opening guidance on the packaging.

Vitamin C is well tolerated by the vast majority of skin types and has no known contraindication for topical use, including during pregnancy and breastfeeding. At high concentrations of the pure form, mild tingling or temporary redness may occur on application: it fades within minutes. Oil-soluble, non-acidic esters don't carry this risk^2,5.

On very reactive skin, patch test behind the ear first, and avoid the immediate eye area with pure formulas. As with any facial treatment, don't apply to broken skin. If in doubt, ask your Yon-Ka esthetician or healthcare professional for advice.