What is vitamin C

One of the most sought-after and misunderstood active ingredients in modern cosmetics. Vitamin C, also known as ascorbic acid, is a powerful antioxidant with decades of clinical research supporting its efficacy in brightening, collagen synthesis, and protection against oxidative damage. It's not hype: it's one of the active ingredients with the most evidence in cosmetics.

The problem is that in its pure form, it is unstable. It oxidizes easily on contact with air and light, which has led the industry to develop more stable derivatives that convert into active ascorbic acid once applied to the skin.

Where does it come from

It is found naturally in fruits and vegetables, especially in citrus fruits, kiwi, and acerola. In cosmetics, these fresh extracts are not used directly because they do not guarantee constant concentration or stability. Vitamin C for cosmetic use is obtained through controlled processes that ensure purity, precise concentration, and stability against oxidation.

The richest natural sources that appear in cosmetic formulations are Kakadu plum, the natural source with the highest known concentration, rosehip, camu-camu, and acerola. Much higher in concentration than oranges.

Forms of vitamin C in cosmetics

Ascorbic acid: the pure form, the most studied and effective, but also the most unstable. It requires a low pH (between 3 and 4) to penetrate the skin well, which can be irritating for very sensitive skin. It needs opaque and airtight packaging.

Stabilized derivatives: chemically modified versions that transform into active vitamin C once on the skin. More tolerable and stable, with a lower risk of irritation. The most common are ascorbyl glucoside, 3-O-ethyl ascorbic acid, and ascorbyl tetraisopalmitate.

How it works

It neutralizes free radicals generated by sun exposure, pollution, and oxidative stress before they can damage skin cells. Unlike other antioxidants that act only on the surface or only inside the cell, ascorbic acid works in both environments.

It participates directly in collagen synthesis: it is an essential cofactor for the enzymes that convert procollagen into mature collagen. Without vitamin C, this process is less efficient. That's why its continued use has a real effect on skin firmness and texture, not just on immediate tone.

It also inhibits tyrosinase, the enzyme responsible for melanin production, which explains its skin tone-evening action and its efficacy on sun and age spots.

Properties and benefits

• Brightness: improves dull and uneven appearance, restoring uniformity and natural radiance.
• Antioxidant action: protects against daily oxidative damage from UV radiation and pollution.
• Stimulates collagen synthesis, contributing to firmness and elasticity with continued use.
• Anti-spot: reduces hyperpigmentation by inhibiting melanin production.
• Anti-aging: improves texture and smooths fine lines with regular use.
• Suitable for all skin types, with greater caution for very sensitive skin where stabilized derivatives are more appropriate.

Use and integration into the routine

In the morning, before sunscreen: that is its ideal time. Vitamin C enhances sun protection by acting as the first antioxidant line against free radicals generated by UV radiation. Applying vitamin C in the morning and sunscreen on top is one of the most effective combinations in active cosmetics.

It combines very well with hyaluronic acidfor simultaneous hydration, with niacinamideto enhance the anti-spot effect (the supposed incompatibility between the two is a myth based on a study from the 60s that is not replicated in modern formulas), and with vitamin E, which stabilizes and enhances its antioxidant action. With bakuchiolor phytoretinolit forms a complete anti-aging routine.

With exfoliating acids like AHA or BHA, it's better to alternate rather than combine in the same application to avoid overwhelming sensitive skin.

Curiosities and facts

Photosensitive is not the same as photosensitizing
This is the most widespread misunderstanding about vitamin C. Photosensitive means that it degrades when exposed to light and air, losing effectiveness. Photosensitizing would mean that it increases the risk of sunburn or sun spots. Vitamin C is not photosensitizing: on the contrary, it helps protect the skin from sun damage. Vitamin C serum that turns brown does not stain the skin; it simply no longer works.

When the serum changes color
A vitamin C serum that turns dark orange or brown has started to oxidize. It is not dangerous, but it has lost its antioxidant efficacy. That's why bottles should be dark and airtight, and it's advisable not to buy very large formats if use is slow.

Kakadu plum
It is the most concentrated source known. This Australian fruit, consumed by Aboriginal people for millennia, has up to 100 times more vitamin C than oranges. It is not a common ingredient in mass cosmetics due to its cost and limited availability, but it appears increasingly in high-concentration natural formulations.

Vitamin C and scurvy changed history
Before vitamin C was identified as an essential nutrient, scurvy killed more sailors on long voyages of exploration than any storm. In 1747, naval physician James Lind showed that consuming citrus fruits prevented the disease, decades before ascorbic acid was identified as the responsible compound. One of the first controlled clinical investigations in history.

As it appears in INCI: Ascorbic Acid, Sodium Ascorbyl Phosphate, Ascorbyl Glucoside, 3-O-Ethyl Ascorbic Acid, Ascorbyl Tetraisopalmitate

Other active ingredients you might be interested in

Niacinamide: anti-spot and tone-regulating, a well-studied combination with vitamin C.
Astaxanthin: the most potent known antioxidant, a very effective anti-aging complement.
Bakuchiol: renewing and anti-aging, a powerful combination for complete anti-aging routines.
Rosehip: natural source of vitamin C and retinoids, complementary profile for spots and regeneration.
Pomegranate: powerful antioxidant, natural complement for protection and even skin tone.