Formulation and evaluation of hydrous and anhydrous skin whitening products containing sodium ascorbyl phosphate and kojic acid dipalmitate

Abstract

In Asia skin lightening products have grown to be the best selling skin care products, whereas in the Western hemisphere, including Europe and North America, the main demand is for the treatment of age spots and skin even toning. For African and Asian women, skin lightening is part of their culture, as lighter skin signifies increased wealth and social status. It is believed that blending vitamin C, or its derivates, with kojic acid, or its esters, could synergistically inhibit melanin synthesis. Kojic acid dipalmitate was chosen over kojic acid, as better product stability is ensured without any colour instability problems. Since vitamin C is very unstable, especially in aqueous solution, sodium ascorbyl phosphate, as a stable vitamin C derivative, was used. In this study, kojic acid dipalmitate and sodium ascorbyl phosphate were incorporated into both hydrous - and anhydrous formulations, in order to compare the stability of these actives in the various formulations that were developed and prepared. A hydrous - and anhydrous gel, a hydrous cream and anhydrous ointment, and a hydrous - and anhydrous stick were formulated. These formulations were subjected to stability testing over a three-month period and storage at three conditions, i.e. 5°C, 25°C + 60% RH, and 40°C + 75% RH. Various stability tests, including HPLC analysis, pH, physical examination, viscosity, relative density, spreadability, penetration, preservative efficacy and membrane release studies were done on these formulations. HPLC analysis proved the kojic acid dipalmitate to be more stable overall in anhydrous formulations. Some formulation problems were experienced with the sodium ascorbyl phosphate, which made it difficult to conclude on the stability of this active in the formulations being evaluated.