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Informations sur le pH de la peau.

Everything You Need To Know About Skin pH.

In the world of cosmetics, the term pH is increasingly used. This is justified, as maintaining the skin pH is essential for healthy skin. But what is pH? Why is pH balance of skin important? Find out in this article.

Summary
Published February 29, 2024, by Sandrine, Scientific Editor — 6 min read

What Is pH?

The hydrogen potential (pH - potentia hydrogenii) of an aqueous solution measures whether it is acidic or alkaline. More specifically, it measures the concentration of oxonium ions (H3O+) in an aqueous solution. The chemical formula linking the two is pH = -log [H3O+].

PH values range from 0 to 14:

  • If the pH is between 0 and 7: it is acidic;

  • If the pH is equal to 7: it is neutral;

  • If the pH is between 7 and 14: it is basic (alkaline).

Thus, the lower the pH level, 

the more acidic the solution, 

and the higher the pH value, 

the more basic the solution.

There are two main methods for measuring the pH of a solution. The first involves the use of pH paper, which changes color according to the pH of the aqueous solution in which it is immersed. The second, more precise method uses pH electrodes connected to a pH meter.

As mentioned above, the pH scale is logarithmic and non-linear. Thus, a pH of 3 is 10 times more acidic than a pH of 4, and 100 times more acidic than a pH of 5.

Skin pH.

The skin is our body's largest organ. It is our body's first line of defense against external aggression. This protective role is made possible by the acidic pH of around 5.5 of the skin's hydrolipidic film. The hydrolipidic film on the skin's surface is a complex emulsion composed essentially of sweat and sebum. The acidic pH of the hydrolipidic film is a key factor in barrier homeostasis, stratum corneum integrity and antimicrobial defense: it's known as the “acid barrier” or “acid mantle”. Ceramides, essential components of the stratum corneum, are synthesized at an acidic skin pH by pH-dependent enzymes.

Skin pH varies according to both endogenous and exogenous factors. Endogenous factors that can cause pH to vary include the following:

  • Age: The skin pH of newborns is much higher than that of adults, with a value close to 7 (neutral pH), and decreasing over time;

  • Skin zones: Skin pH is higher in certain areas of the body (armpits, groin, intra-mammary area…). In the armpits, a higher pH leads to colonization by certain resident odor-producing bacteria, such as propionic bacteria and staphylococci. Deodorants containing citrates reduce pH and inhibit bacterial activity;

  • Skin type: Teenagers with oily, acne-prone skin have a rather alkaline pH.

Other endogenous factors, such as gender or skin pigmentation, can also vary the pH. Because men produce more sebum and sweat than women, their skin pH is more acidic. What's more, it has been proven that people with more matte skin have a more acidic skin pH, due to a greater presence of epidermal lipids. In addition to endogenous factors, there are exogenous factors that can vary the pH balance of skin. These include

  • Certain cosmetic products: most soaps, for example. They have a basic pH of around 9 – 10, which disturbs the natural acid pH of the hydrolipidic film. This results in dry skin and the risk of infection, meaning that the pH balance is off level.

Please note: Unlike soaps, which have a basic pH that disrupts the skin's pH, cosmetics with an acidic pH of between 3 and 4, such as vitamin C or fruit acid-based products, are beneficial for the skin. This is due to the fact that the enzymes responsible for producing ceramides (lipid constituents of the skin barrier) have an optimal acidic pH. In this way, they help strengthen the skin barrier. But be careful! Some products, such as lemon juice, whose properties are touted on the Internet, have a pH that is too acidic (2.4) and are therefore irritating to the skin.

It can have unfortunate consequences when the pH balance is off. It is therefore important to use cosmetic products with a pH between 3 and 7.

Source :

  • YOSIPOVITCH G. & al. Skin pH : From basic science to basic skin care. Acta Dermato-Venereologica (2013).

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