How To Regulate pH Balance of Your Skin?

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”.

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 with age;

• 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 skin pH.

Other endogenous factors, such as gender or skin pigmentation, can also vary the pH. In addition to endogenous factors, exogenous factors can vary skin pH. These include

• Certain cosmetic products: soaps, for example. Soaps, for example, have a basic pH of around 9 – 10, which disturbs the natural acid pH of the hydrolipidic film, resulting in dry skin and the risk of infection.

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. Their enzymes responsible for ceramides production (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.

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

As a reminder, the skin's acid pH preserves the integrity and cohesion of the stratum corneum and protects the skin from microbial infection. In fact, when skin pH rises, the enzymes responsible for ceramides production, which have an optimal acid pH, are inactivated, compromising the structure and function of the stratum corneum. Moreover, while lipid-synthesizing enzymes decrease, other enzymes increase at acid pH: serine proteases. The latter lead to a reduction in corneodesmosomes, by degradation of desmoglein-1, whose role is to ensure the cohesion of stratum corneum elements.

When the pH of the skin is deregulated, 

the skin is no longer resistant to external 

aggression and does not retain its moisture.

This is conducive to the development of dermatoses such as atopic dermatitis. Indeed, it has been shown that the higher the pH, the more intense the itching and the greater the dryness. In addition to the fact that in atopic dermatitis the structure of the stratum corneum is altered, colonization by Staphylococcus aureus is a common feature of affected patients and is considered a major pathogenic factor in atopic dermatitis. Staphylococcus aureus adhesion to human keratinocytes increases with rising pH.

The growth of protective bacteria in the skin microbiota is optimal at acidic pH levels, whereas pathogenic bacteria thrive at neutral and basic pH levels (Staphylococcus aureus, Cutibacterium acnes). As a result, deregulation of skin pH disrupts the microbiota and prevents antimicrobial protection. This increases the risk of infection. Furthermore, serine proteases, which are activated by high pH, lead to the synthesis of cytokines that cause inflammation.

Preserving the skin's pH is therefore essential to maintaining the integrity of the stratum corneum and the skin's protective role.