Sodium Ascorbyl Phosphate

What is sodium ascorbyl phosphate?

Sodium ascorbyl phosphate is a precursor of ascorbic acid. It is generated from ascorbic acid by the introduction of a phosphate group into the second position of the cyclic ring (R).

Is sodium ascorbyl phosphate stable?

Sodium ascorbyl phosphate has improved stability over ascorbic acid, making it better-suited for use as an active ingredient in cosmetic preparations. It is also more stable than ascorbyl palmitate and at least as stable as magnesium ascorbyl phosphate (R, R), 2 other derivatives of ascorbic acid.

Temperature and pH are the most important factors affecting the stability of sodium ascorbyl phosphate (R). Refrigeration has been shown to extend the shelf life of emulgels containing 5% sodium ascorbyl phosphate, and to prevent yellowing (R). Neutral or basic solutions have the highest stability, whereas in acid solution sodium ascorbyl phosphate may be easily hydrolysed to ascorbic acid and inorganic phosphate (R).

The addition of 0.125% of the antioxidant preservative sodium metabisulfite has also been demonstrated to increase the stability of sodium ascorbyl phosphate formulations (R).

Does sodium ascorbyl phosphate get absorbed?

Experiments on pig ear skin and human skin have shown that sodium ascorbyl phosphate is able to penetrate through the epidermis (R, R). The carrier system matters, for sodium ascorbyl phosphate penetrates the epidermis significantly better from liposome dispersions than from aqueous solution (R). Microemulsions are also suitable carrier systems for the topical application of sodium ascorbyl phosphate (R). In addition, laser pretreatment and electrotreatment can increase the delivery of sodium ascorbyl phosphate to the skin (R, R).

What happens to sodium ascorbyl phosphate after absorption?

To achieve favourable effects on the skin, ascorbic acid has to be liberated from sodium ascorbyl phosphate by enzymatic degradation in the skin (R). There is evidence that this does occur.

For instance, mouse skin was cultured in a medium containing sodium ascorbyl phosphate, the concentration of ascorbic acid in the skin tissue increased and remained elevated for up to 24 hours, even though intact sodium ascorbyl phosphate was not detected in the skin cells. It has therefore been suggested that skin cells continuously take up sodium ascorbyl phosphate and convert it to ascorbic acid through dephosphorylation via the action of acid phosphatase in the epidermis (R).

Human skin treated with 2% sodium ascorbyl phosphate also had markedly higher epidermal ascorbic acid content than skin treated with 2% ascorbyl glucoside, indicating that the hydrolysis rate of sodium ascorbyl phosphate is much higher (R).