Did you know that in the laboratory, pure vitamin C entered the skin only from formulations with a pH below 3.5?
An antioxidant that is hard to formulate
Ultraviolet light generates reactive oxygen species in the skin, which contribute to sun damage and photoaging. Antioxidants help the skin defend itself against this stress, and vitamin C is one of the most studied.
The skin already has its own reserve of vitamin C. The idea behind applying it in a cream or serum is to top up this reserve. For that to work, though, vitamin C has to get into the skin, and this is far from guaranteed.
How the study was done
The study, published in 2001, was carried out in the laboratory on pig skin, a model often used because it is similar to human skin. The researchers applied vitamin C as L-ascorbic acid, or some of its derivatives, in different formulations.
They then measured how much vitamin C was found in the skin, to understand which features of a formula allow it to be absorbed.
What was observed
L-ascorbic acid entered the skin only when the formula had a pH below 3.5. Absorption was greatest at a concentration of 20%. Levels in the skin peaked after three daily applications, and once application stopped they halved in about four days.
The vitamin C derivatives tested, magnesium ascorbyl phosphate, ascorbyl palmitate and dehydroascorbic acid, did not increase the levels of L-ascorbic acid in the skin. The authors conclude that the delivery of vitamin C into the skin depends critically on the features of the formulation.
How to read the result
This is a laboratory study on animal skin, and it measures absorption without assessing the effect on the appearance of the skin. It does show clearly that the name of an ingredient on a label is not enough to tell whether, and how much of it, will reach the skin.
A very acidic pH and high concentrations can also irritate some skin types. That is why choosing a vitamin C product should take your own tolerance into account. If your skin is sensitive or reacts easily, ask a dermatologist for advice.
This article is for information only. It does not replace the advice of a doctor or dermatologist, whom you should consult with any question about your skin.