Mastering the formulation of an unstable vitamin C (VC) as anti-aging skin care ingredient. Part I: A new approach

Objective

To develop a stabilized 12% pure Vitamin C-based serum at a pH close to that of the skin for use in anti-aging.

Material and Methods

At acidic pH (<3), under oxidative conditions, the ascorbate anionic form of VC rapidly undergoes transformations leading to a Xylosone by-product, resulting in important chemical losses of VC. Buffering the ascorbate anionic moiety with alkaline agents largely decreases its transformation and the loss of VC. The use of a cationic polymer (Polyquaternium 67, PQ67) enables binding of the ascorbate anion by creating an ionic network, at pH 6 and slows down the slight yellowing of the serum.

Results

By exposing this complex to a temperature of 45°C for a two-month period, more acceptable degradation was obtained, with less VC chemical loss (approx. 5%–10%). Although a slight yellowish colour developed, it was found non redhibitory through consumer tests. As a result, such combination still leaves an important concentration of pure VC (over 10%) likely able to express its efficacy as anti-aging ingredient. Further refinements of this association were performed to reach adequate organoleptic properties of the formula, in view of a future clinical test, as proof of performance of VC efficacy at pH 6.

Conclusion

The stabilized formulation of VC at a pH close to that of the skin, apt at being tested in vivo, offers new possibilities for skin anti-aging routines strategy, by avoiding too acidic conditions (∼pH 3 or below) in daily use cosmetics and thereby allowing better tolerance and an increased adherence of the consumers.