What Is Vitamin C, What Does It Do? Ascorbic Acid and Its Derivatives

The antioxidant strength of L-ascorbic acid and its quick spoiling in a bottle come from the same chemical property: it readily gives up an electron. When it gives one to a free radical, it protects the cell; when it gives one to oxygen in the air, the serum loses its strength. The human body cannot make this vitamin itself and must obtain it from food. For serum choice and the morning routine, see the vitamin C serum guide; here we focus on the molecule itself.

Where does the skin hold vitamin C?

In the skin, vitamin C is found mostly in the top layer, the epidermis. Its level is 2-5 times higher than in the underlying dermis. Measurements vary from study to study by about 10 times, but the difference is consistently reported. The molecule enters cells through two transporter proteins (SVCT1 and SVCT2) that work with sodium; both are found in epidermal cells. UV light lowers the level in the skin.

Views differ on the question of whether it comes from food or from application. One review argues that in people with low levels, diet raises skin levels, while if blood levels are saturated, an applied product adds little. One study found that 3 grams of daily supplement doubled levels in skin cells within 6 weeks; this is a measurement condition, not a dose recommendation. Pig skin measurements, meanwhile, show that a low-pH serum raised skin levels, and that after stopping, these levels fell with a half-life of about 4 days. Since there is no strong comparison in human skin to settle the question, it is more correct not to substitute one for the other.

Role in collagen production

Vitamin C is an auxiliary molecule for two enzymes (prolyl and lysyl hydroxylase) that add hydroxyl groups to the proline and lysine amino acids in collagen chains. Without this step the triple helix of collagen cannot remain stable at body temperature. The most striking example of deficiency is scurvy: skin becomes fragile, gums bleed, hairs curl like corkscrews, and wounds heal slowly.

Its role is not limited to these enzymes. In laboratory data, vitamin C increases the reading of collagen genes, stabilises the precursor signal of type I and III collagen, and increases a protein that restrains the collagen-breaking enzyme MMP-1. It suppresses elastin production in the laboratory. These strengthen the biological rationale, but do not alone show that an applied serum produces an effect of the same size.

Which effect has human data?

The distance between mechanism and clinical result is not the same for every heading. Look at the last column when reading the table. For expectations on timing, also keep in mind that most anti-ageing products need at least 6 weeks for an effect.

What does it do as an antioxidant, and what can't it do?

Vitamin C is the most abundant antioxidant in human skin and neutralises free radicals by donating electrons. Since it is water-soluble, it works in the aqueous regions of the cell, and it also restores vitamin E when the latter, which protects oily membranes, is oxidised. This division of labour explains why combination formulas are studied: in pig skin, 15% vitamin C and 1% vitamin E raised the UV protection factor by about 4 times, and when 0,5% ferulic acid was added, this value reached 8 times.

What it cannot do is block UV light, so it carries no SPF value. According to one measurement, sunscreens can block about 55% of UV-induced free radicals. An antioxidant can support this gap, but it does not replace sunscreen. Applying a broad-spectrum product of at least SPF 30 and renewing it every 2 hours and after sweating or swimming is still necessary.

Why is L-ascorbic acid so unstable?

The molecule that meets oxygen first converts into dehydroascorbic acid, and gives the solution a yellow colour. Light, heat and metal ions accelerate the process. In a living cell, glutathione can reverse this oxidised form; in a bottle there is no such support.

The low-pH rule also comes from chemistry. When the molecule carries an electric charge, it struggles to pass through the oily environment of the stratum corneum. When the pH falls below 3,5, both penetration and stability improve. The effect does not increase indefinitely with a rising concentration: no additional gain is seen above 20%, while irritation may increase. The lower limit is more debated. One review points to above 8% for biological significance, while small human studies have also reported positive results at 3-5%. How to read the colour and storage conditions is explained in detail in the guide article.

Methods such as nanoparticles, multilamellar microemulsions, ultrasound and iontophoresis have also been tried to improve penetration. Studies combining it with laser and microdermabrasion also exist. All of these are small and not compared with each other, so the phrase "advanced carrier" alone is not proof of efficacy.

Derivatives: What is given up in exchange for stability?

Manufacturers try to resolve this instability by attaching another part to the molecule. The gain is shelf life; the cost is that it must first convert to ascorbic acid in the skin. The speed of this conversion is not well known for most derivatives.

The "vitamin C" written on the front therefore says little on its own. The rates and results learned for L-ascorbic acid cannot be transferred directly to its derivatives.

What are the side effects, and who should be careful?

Most people use vitamin C without problems. Stinging, redness and dryness are rare; dryness can be eased with a moisturiser. An oxidised product may leave a slight yellowish colour and stains on clothing. Urticaria and erythema multiforme have been reported very rarely. Care is needed around the eye area.

Low pH may sting more on sensitive skin, or in rosacea or eczema. In this case, try the new serum first on the inner arm or elbow crease, twice a day, for 7-10 days, and consult your dermatologist before starting. A high concentration is not a goal in itself; a product you can use regularly works better.