Sodium Ascorbyl Phosphate

The most researched derivative of vitamin C. It boosts collagen synthesis, thereby improving skin structure and elasticity. SAP is effective in the treatment of inflamed acne lesions and has a weak but positive effect on pigmentation issues.
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Sodium Ascorbyl Phosphate

Overview

Sodium ascorbyl phosphate (SAP) is a derivative of vitamin C. It is one of the best-researched derivatives and has a multitude of benefits for the skin.

You can read more about regular ascorbic acid (AA) here - Ascorbic Acid - to learn about its mechanism of action. In short, it is a skin-natural antioxidant, collagen boosting, and anti-pigment ingredient that unfortunately has some major stability and skin penetration problems.

Ascorbic acid derivatives such as SAP were developed in an attempt to resolve these issues and develop a more potent and practical version of vitamin C for use in skincare products.

Sodium ascorbyl phosphate, like ascorbic acid, is water-soluble, but dramatically different in its range of stability. SAP is most stable at neutral and basic pH levels and is more resistant towards light and oxygen, whereas AA is only stable at a very acidic pH level. This is a benefit to people with more sensitive skin who cannot tolerate highly concentrated and acidic AA serums.

SAP also has a much longer shelf life. In a storage degradation experiment, there was still 60% of the SAP left intact in the skincare product after 30 months, whereas ascorbyl palmitate was completely gone after 11 months. SAP has only limited absorption through the skin, but this can be improved through the use of nanoemulsions or liposomes as a delivery system.

SAP is converted into active ascorbic acid after absorption and can then be utilized in antioxidant protection and collagen synthesis.

There is one older study made in test tubes that compared SAP with a similar ingredient, Magnesium ascorbyl sulphate (MAP). It found that while MAP was almost just as effective at stimulating collagen production as AA, SAP was tenfold less effective.

There are multiple clinical studies involving SAP that can help us to understand its benefits.

The first study was performed on 12 women with crow's feet wrinkles. It found that a 5% SAP emulgel was just as effective as a 5% AA emulgel in improving the appearance of the wrinkles, although the SAP was significantly more stable (though it also still needed some stabilizing ingredients). All subjects had improved skin structure and elasticity.

Another study used a 6% SAP lotion for the treatment of sun-induced discoloration on 27 Japanese women over a period of 24 weeks. It found that the SAP lotion had a weak, but significant, positive effect on the pigmentation issues.

Lastly, there is a lot of research on the use of SAP for the treatment of acne. Two clinical studies, one with 20 subjects and the other with 37, showed that a 5% SAP lotion was effective in the treatment of inflamed acne lesions.

It is believed that SAP not only has direct antimicrobial activity but also helps, using its antioxidant activity, to prevent the inflammation and formation of comedones.

Another study compared the efficacy of SAP to retinol and found that 5% SAP is as effective as 0,2% retinol in treating inflamed acne. It was also found that these concentrations of actives work well together.

Science

1
Dong, X., Zhang, T., Wei, H., & Dang, L. (2020). Stability of sodium ascorbyl phosphate in the water-glycerol system. Journal of pharmaceutical and biomedical analysis, 181, 113103.
2
Segall, A. I., & Moyano, M. A. (2008). Stability of vitamin C derivatives in topical formulations containing lipoic acid, vitamins A and E. International journal of cosmetic science, 30(6), 453–458.
3
Stamford N. P. (2012). Stability, transdermal penetration, and cutaneous effects of ascorbic acid and its derivatives. Journal of cosmetic dermatology, 11(4), 310–317.
4
Spiclin, P., Homar, M., Zupancic-Valant, A., & Gasperlin, M. (2003). Sodium ascorbyl phosphate in topical microemulsions. International journal of pharmaceutics, 256(1-2), 65–73.
5
Foco, A., Gasperlin, M., & Kristl, J. (2005). Investigation of liposomes as carriers of sodium ascorbyl phosphate for cutaneous photoprotection. International journal of pharmaceutics, 291(1-2), 21–29.
6
Nayama, S., Takehana, M., Kanke, M., Itoh, S., Ogata, E., & Kobayashi, S. (1999). Protective effects of sodium-L-ascorbyl-2 phosphate on the development of UVB-induced damage in cultured mouse skin. Biological & pharmaceutical bulletin, 22(12), 1301–1305.
7
Geesin, J. C., Gordon, J. S., & Berg, R. A. (1993). Regulation of collagen synthesis in human dermal fibroblasts by the sodium and magnesium salts of ascorbyl-2-phosphate. Skin pharmacology : the official journal of the Skin Pharmacology Society, 6(1), 65–71.
8
Mohammadi, S., Shokri, J., Ranjkesh, M., Akbari Hamed, S., & Monajjemzadeh, F. (2021). Comparative physicochemical stability and clinical anti-wrinkle efficacy of transdermal emulgel preparations of 5% sodium ascorbyl phosphate and or ascorbic acid on human volunteers. Journal of cosmetic dermatology, 20(1), 174–180.
9
Ishikawa, Y., Niwano, T., Hirano, S., Numano, K., Takasima, K., & Imokawa, G. (2019). Whitening effect of L-ascorbate-2-phosphate trisodium salt on solar lentigos. Archives of dermatological research, 311(3), 183–191.
10
Klock, J., Ikeno, H., Ohmori, K., Nishikawa, T., Vollhardt, J., & Schehlmann, V. (2005). Sodium ascorbyl phosphate shows in vitro and in vivo efficacy in the prevention and treatment of acne vulgaris. International journal of cosmetic science, 27(3), 171–176.
11
Woolery-Lloyd, H., Baumann, L., & Ikeno, H. (2010). Sodium L-ascorbyl-2-phosphate 5% lotion for the treatment of acne vulgaris: a randomized, double-blind, controlled trial. Journal of cosmetic dermatology, 9(1), 22–27.
12
Ruamrak, C., Lourith, N., & Natakankitkul, S. (2009). Comparison of clinical efficacies of sodium ascorbyl phosphate, retinol and their combination in acne treatment. International journal of cosmetic science, 31(1), 41–46.