Where Vitamin C Derivatives Actually Sit in the Skin: A Mass-Spectrometry Study of Ethyl Ascorbic Acid and Ascorbyl Glucoside

Many Indian vitamin C serums do not use pure L-ascorbic acid at all. They use derivatives such as 3-O-ethyl ascorbic acid or ascorbyl glucoside, which are more stable in the bottle. A recurring question is how far those molecules actually travel once they are on the face. A study published online on 23 September 2026 in the International Journal of Pharmaceutics offers a detailed, if small, look.

Researchers at the University of Nottingham's School of Pharmacy, working with two scientists from the No7 Beauty Company at Boots, applied serums to the skin of three healthy female volunteers. One serum contained 3-O-ethyl ascorbic acid together with the peptide blend sold as Matrixyl 3000, and was left on for half an hour, two hours or five hours. A second serum containing ascorbyl glucoside was left on for half an hour. The team then removed the outer layer of skin, the stratum corneum, strip by strip with adhesive tape and analysed each strip using two forms of secondary ion mass spectrometry, which can map where specific molecules are.

For ethyl ascorbic acid, the signal fell steadily with depth at every exposure time, meaning most of it stayed close to the surface. Imaging showed it was not spread evenly but concentrated along the boundaries between skin cells. Ascorbyl glucoside showed a different pattern, consistent with moving into the cells themselves. The two peptides were detected in every layer sampled but appeared to stay on the outer surfaces of cells rather than inside them, with little change between short and long exposures.

The authors' broader point is that the usual shortcut for predicting skin penetration, how oily or water-loving a molecule is, did not fully explain which route each ingredient took.

This was not an efficacy study. It measured location, not brightening, collagen or any visible change, and only in the outermost layer of skin. Three volunteers is a very small group, and the findings apply to these particular formulations rather than every serum using the same ingredients. Two of the authors are employed by Boots, which sells skincare containing such actives; the paper declares no competing interests.