Carbon Dioxide in Cosmetics

We all know that the age-accelerating oxidative damage is the result of pernicious actions by reactive oxygen species (ROS) such as hydrogen peroxide, superoxide anion radical, hydroxyl radical and singlet oxygen, while molecular oxygen is more of a necessary, helpful molecule. Indeed, if we were to take a poll to select the longevity molecule number one, we might very well expect that the general consensus would materialize around molecular oxygen, O₂. This might well explain why so much research is devoted to technologies aiming at using oxygen in skin care, such as for instance, the application of hyperbaric oxygen. Indeed, oxygen taken up from the environment, or from a topically applied concoction able to release molecular oxygen, would fight anoxia and avoid spider and varicose veins. It would also boost cellular metabolism, thus keeping ATP synthesis and membrane potential at homeostatic levels. It would also avoid cellular necrosis and the consequent microinflammatory response that is the most efficient single mechanism leading to skin aging.

In this frame of thinking, a strong, eye-catching claim was made for a very recent skin care product. The product is said to release carbon dioxide (CO₂) to boost oxygen and achieve a totally hydrated, firm and bright skin. And, my eye was caught, and I have a few questions about it.

Biochemistry of CO2

We know since high school chemistry class that all the metabolic pathways of animal cells end up in releasing the ultimate trash that consists of urea and CO₂. Since urea has been used as a moisturizer, it is not to be excluded a priori that carbon dioxide, despite its environmental ill repute, might be of use in skin care. 

And yet, the idea of dipping the skin in an atmosphere rich in carbon dioxide appears preposterous. First, because our skin is not equipped with the photosynthetic complex characteristic of plants, that would allow the release of a rush of oxygen from carbon dioxide. And then because, by exposing the skin to excess carbon dioxide, one might hinder the uptake of molecular oxygen from the environment. This would limit the access of oxygen to skin  cells and decrease energy production in those epidermal cells that receive oxygen from the environment and not from the blood.
Finally, we know that oxygen and CO₂ bind to hemoglobin in different sites. We also know that the pH of the blood decreases when the level of CO₂ increases, and that at lower pH the conformation of hemoglobin changes, the affinity of oxygen for hemoglobin is decreased and oxygen is released. 

So, while hindering the uptake of oxygen from the outside, an increase of carbon dioxide around the skin would squeeze all the oxygen out of red blood cells, but this is already happening “naturally”! And I am not sure that this excess CO₂ is able to extract residual oxygen from erythrocytes… if any is left. I do not see what kind of rush of oxygen can be provoked by a product providing extra carbon dioxide to the skin.

This is one point, but I do not rest my case. I do have another questions: where does the carbon dioxide come from?

One might recall how an antacid drug such as magnesium carbonate (MgCO₃) does work. In the presence of an acid such as hydrochloric acid (HCl) that can be abundant in the stomach, orally administered magnesium carbonate forms magnesium chloride, water and carbon dioxide. 

Well, but…If we put an acid in a formula containing magnesium carbonate, CO₂ will be released quite quickly, perhaps making bubbles in the formula, and will no longer be available at the moment of the topical application. So the acid must be “generated” at earliest, after the topical application. How do we do that?

One might think: “Aha! The skin is acid! Let us put magnesium carbonate on the skin and as soon as the product hits the stratum corneum, we will release a rush of carbon dioxide!” Unfortunately, that will not work. The skin is far from being acid. The pH of the stratum corneum is closer to 7 or 8 that to 5 or 6¹ and there are not many chances that in a non-acidic environment, magnesium carbonate will undergo the process described above.

Conclusion

This is a discussion from first principles and, as such, it will always be susceptible to criticisms and disagreements. A good friend of mine used to say: “The proof is in the pudding.” 

The brands introducing products as releasers of carbon dioxide to drench the skin in oxygen should provide a description of a clinical test, easy to perform, indicating the kinetic release of carbon dioxide upon topical application of the product, and the consequent rush of oxygen. The quantitative description of the cutaneous benefits would also be welcome. 

Without such or similar tests, the systematic doubt about those eye-catching claims remains mandatory.

Paolo Giacomoni, PhD

Insight Analysis Consulting
[email protected]

Paolo Giacomoni acts as an independent consultant to the skin care industry. He served as Executive Director of Research at Estée Lauder and was Head of the Department of Biology with L’Oréal. He has built a record of achievements through research on DNA damage and metabolic impairment induced by UV radiation as well as on the positive effects of vitamins and antioxidants. He has authored more than 100 peer-reviewed publications and has more than 20 patents. He is presently Head of R&D with L.RAPHAEL—The science of beauty—Geneva, Switzerland.

References

1. Giacomoni PU (2020) Stratum corneum pH is closer to 7 than to 5. J Cosmet. Dermatol 19 : 1793-1794