As soon as l-ascorbic acid is mixed with water it starts oxidizing. This makes the l-ascorbic acid ineffective and also dangerous, because oxidized L-ascorbic acid is a pro-oxidant which may increase the formation of free radicals.

So, the challenge has been to make stable L-ascorbic acid products, or to make l-ascorbic acid itself stable.

Currently there are three ways this has been done:The Skinceuticals Vitamin C Plus Ferulic Acid + Vitamin E formulation, Anhydrous C: and 

Tetrahexyldecyl Ascorbate ( Ascorbyl Tetraisopalmitate)

Tetrahexyldecyl Ascorbate is the latest development in Vitamin C derivatives.

Tetrahexyldecyl Ascorbate is oil soluble, just like your skin, which means that it easily penetrates into the skin.

It is not acidic and it does not require a low pH to get it to penetrate the skin, so it does not sting. It is also stable in air and water for up to 18 months, which means it will work as an anti-oxidant long after you start using it.

Studies have shown that Tetrahexyldecyl Ascorbate is an effective skin care product. It effectively suppresses UVB-induced skin pigmentation, possibly through its anti-oxidative activity.

Tetrahexyldecyl Ascorbate also prevented UVA induced oxidative stress, and it boosted collagen synthesis.

Magnesium Ascorbyl Phosphate is a water-soluble vitamin C derivative. Magnesium Ascorbyl Phosphate is not acidic so it does not irritate the skin and it is more stable than vitamin C.

Studies have shown that Magnesium Ascorbyl Phosphate is JUST as effective at boosting skin collagen synthesis as L-ascorbic acid.

Magnesium Ascorbyl Phosphate has proven to be an effective skin lightener, reducing hyperpigemnetation in some test subject.

Finally, studies have shown that Magnesium Ascorbyl Phosphate protects against UVB induced skin damage, such as inflammation and free radical formation, both duuring and after exposure to sunlight.

Ethyl ascorbic acid

Ethyl ascorbic acid is a novel vitamin C derivative with excellent whitening, anti- oxidation, radicals scavenging and collagen increasing effect.

Its stability is superior to other ascorbic acid derivatives. Is widely used in skin care products, especially desirable for whitening and anti-ageing products

It has been shown to reduce the appearance of age-spots and also increase collagen synthesis.

Ascorbic Acid 2-Glucoside

Ascorbic Acid 2-Glucoside(AA2G) is natural vitamin C (ascorbic acid) stabilized with glucose. This combination allows the benefits of vitamin C to be conveniently and effectively used in cosmetic products.

Ascorbic Acid 2-Glucoside is water soluble and extremely stable!

When creams and lotions containing Ascorbic Acid 2-Glucoside (AA2G) are applied to the skin, an enzyme present in the skin, a-glucosidase, acts on the Ascorbic Acid 2-Glucoside(AA2G?? to slowly release the healthful benefits of vitamin C. 

Ascorbic Acid 2-Glucoside (AA2G) was originally developed as a quasi-drug cosmetic product in Japan to lighten the overall tone of the skin and reduce the pigmentation in age spots and freckles.

Further research has shown other dramatic benefits and today Ascorbic Acid 2-Glucoside (AA2G)  is used all over the world  not only for whitening but also for brightening dull looking skin, reversing the effects of aging, and in sunscreen products for protection.

Vitamin C derivatives: 

To improve the stability of vitamin C in skin care, scientists have been looking for alternative solutions. One of these has been to create Vitamin C derivatives. Usually these are made by combining ascorbic acid with other molecules. Examples of these are the water soluble Magnesium Ascorbyl Phosphate and the oil soluble Tetrahexyldecyl Ascorbate (which is also known as Ascorbyl Tetraisopalmitate)

Sodium Ascorbyl Phosphate

Sodium Ascorbyl Phosphate is a stable vitamin C derivative. It protects the skin,
promotes its development and improves its appearance.

Sodium Ascorbyl Phosphate is cleaved enzymatically in the skin to release active vitamin C.

Sodium Ascorbyl Phosphate is therefore an effective antioxidant which protects
the cells against damage caused by free radicals.

Sodium Ascorbyl Phosphate counteracts skin aging in promoting collagen formation.

Sodium Ascorbyl Phosphate also acts on the melanine formation process to
prevent hyperpigmentation and senile keratosis. It therefore has skin lightening
properties.

Because of its wide spectrum of action, Sodium Ascorbyl Phosphate is suitable
for use in a wide range of skin care products.