The skin is a complex organ whose balance depends on numerous biological parameters. Among them, skin pH plays an essential role in maintaining the skin’s protective functions.
Although this term is often mentioned in the field of cosmetic skincare, its true importance is sometimes misunderstood. Yet the pH of the skin influences several fundamental mechanisms, including the skin barrier, enzymatic activity and the balance of the skin microbiome.
Understanding this parameter helps to adopt a more attentive approach to skincare and to better appreciate the factors that may influence the skin’s balance.
What is pH?
pH, or potential of hydrogen, is a measure indicating the degree of acidity or alkalinity of a solution.
The pH scale generally ranges from 0 to 14:
- a pH below 7 indicates an acidic environment
- a pH of 7 corresponds to a neutral environment
- a pH above 7 indicates an alkaline environment.
The surface of the skin naturally has a slightly acidic pH, generally between 4.5 and 5.5 (Lambers et al., 2006).
This acidity is often referred to as the skin acid mantle.
The acid mantle: a natural protection
The acid mantle corresponds to a thin protective layer present on the surface of the skin. It results from the interaction of several elements:
- sebum
- sweat
- skin lipids
- organic acids
- products of cellular metabolism.
This layer contributes to several essential functions.
Protection against certain micro-organisms
A slightly acidic environment helps limit the proliferation of certain potentially undesirable microorganisms. It also favours the presence of commensal bacteria that contribute to the balance of the skin microbiome.
Maintaining this pH therefore supports the balance of the skin’s microbial ecosystem.
Support for the skin barrier
pH also influences the organisation of lipids present in the stratum corneum, the outermost layer of the skin.
These lipids play a central role in the structure of the skin barrier. When pH moves away from its physiological level, certain enzymes involved in the formation of these lipids may be affected.
This may influence the skin’s ability to limit transepidermal water loss and to protect itself against external aggressors (Fluhr et al., 2001).
Enzymatic activity in the skin
Several enzymes present in the stratum corneum participate in essential processes for the skin, including:
- natural desquamation
- cellular renewal
- the formation of skin lipids.
The activity of these enzymes partly depends on the pH of the skin environment.
A pH that is too high may alter their activity and influence the natural process of skin renewal (Hachem et al., 2003).
Maintaining a pH close to the skin’s physiological level therefore helps support the skin’s natural mechanisms.
The impact of external factors
Skin pH may be influenced by various external factors.
Cleansing and skincare products
Some cleansing products may have a higher pH than that of the skin.
Repeated exposure to alkaline products may temporarily modify skin pH. However, the skin has natural mechanisms that allow it to gradually restore its balance.
In some cases, formulations designed with a pH close to that of the skin may help preserve this balance.
Environmental factors
The environment may also influence skin pH.
For example:
- atmospheric pollution
- climatic variations
- UV exposure.
These factors may interact with the skin surface and influence certain physiological parameters.
Age and skin pH
Skin pH may also evolve throughout life.
In infants, the skin initially has a pH closer to neutrality. It gradually becomes more acidic during the first weeks of life.
In adults, some studies suggest that skin pH may slightly increase with age, which could influence certain functions of the skin barrier (Lambers et al., 2006).
pH and skin sensitivity
Maintaining a physiological pH is often associated with better skin tolerance.
A higher pH may favour certain phenomena:
- disruption of the skin barrier
- alteration of the microbiome
- increased transepidermal water loss.
These changes may contribute to increased skin reactivity, particularly in individuals with sensitive skin (Darlenski & Fluhr, 2012).
Cosmetics and respect for skin pH
In the cosmetic field, the question of pH is particularly important in the formulation of certain products, including:
- cleansers
- exfoliants
- certain active skincare products.
Formulators often aim to design products whose pH is compatible with skin physiology.
The objective is not to permanently modify the skin’s pH, but rather to limit disturbances that could affect its balance.
A balanced approach to skincare
Understanding the importance of skin pH encourages a more attentive approach to skincare.
Certain practices may help preserve this balance:
- favouring gentle cleansers
- avoiding overly aggressive practices
- respecting the skin’s individual sensitivity
- adopting a consistent skincare routine.
Each skin is unique. Observing how it reacts and adapting habits accordingly may help maintain a more stable skin environment.
Conclusion
Skin pH is an essential component of skin balance. By maintaining a slightly acidic environment, the skin supports several fundamental functions:
- protection against certain external aggressors
- balance of the skin microbiome
- organisation of the skin barrier
- enzymatic activity.
Several factors may influence this parameter, including the environment, skincare habits or the natural evolution of the skin.
Understanding these mechanisms allows for a more respectful approach to skin physiology and helps to better understand the skin’s needs in daily care.
Scientific references
Lambers H., Piessens S., Bloem A., Pronk H., Finkel P. (2006). Natural skin surface pH is on average below 5, which is beneficial for its resident flora. International Journal of Cosmetic Science.
Fluhr J.W., Elias P.M. (2001). Stratum corneum pH: formation and function of the acid mantle. Dermatology.
Hachem J.P. et al. (2003). pH directly regulates epidermal permeability barrier homeostasis and stratum corneum integrity. Journal of Investigative Dermatology.
Darlenski R., Fluhr J. (2012). Influence of skin barrier function on sensitive skin. Experimental Dermatology.