On the stability of ascorbic acid in emulsified systems for topical and cosmetic use

Several O/W microemulsions, O/W and W/O emulsions and a W/O/W multiple emul sion were prepared using non-ionic, non-ethoxylated, skin compatible emulsi fiers. Ascorbic acid (vitamin C) was added to the emulsified systems and it s stability against oxidation was studied at 45.0 degrees C in aerobic cond itions and compared with that in aqueous solutions at different pH values. All emulsified systems provided protection to ascorbic acid, as its degrada tion rate, which increased with increasing pH, was slower in emulsified sys tems than in aqueous solutions. The highest protection of ascorbic acid was when it was dissolved in the inner aqueous phase of the W/O/W multiple emu lsion, both at 45 and at 20 degrees C for long storage. A pseudo first-orde r mechanism was hypothesised for ascorbic acid degradation in the experimen tal conditions for as long as abundant dissolved oxygen was present. (C) 19 99 Elsevier Science B.V. All rights reserved.