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Une relation entre pH et pores dilatés ?

A relationship between pH and enlarged pores?

The term pH is an acronym for "potential hydrogen". It refers to the acid-alkaline ratio of a substance, ranging from zero (most acidic) to 14 (most alkaline), with 7 as the neutral position. The skin's pH is typically acidic, falling between 4 and 6, while the body's internal environment maintains a neutral to slightly alkaline pH (around 7.4). What are the implications of a disrupted skin pH on the overall condition of the skin, and more specifically on acne and pore enlargement? Let's delve into this.

The skin's pH, in brief.

The skin is the largest organ in our body. It's the first line of defense of our body against external influences. This protective function is made possible by the acidic pH of about 5.5 of the hydrophilic lipid membrane of the skin. This observation established by researcher Marchionini in 1929 has been confirmed by subsequent studies, notably those of Korting in 1992.

The hydrolipidic film on the surface of the skin is a complex emulsion primarily composed mainly of sweat and sebum. The acidic pH of the hydrolipidic film is an important factor in the homeostasis of the barrier, the integrity of the horny layer, and antibacterial defense. This is referred to as the acid mantle of the skin.

The skin's pH varies depending on both endogenous and exogenous factors. Among the endogenous factors, we can mention:

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

  • Skin Zones : The pH of the skin is higher in certain areas (armpits, groin, intra-mammary area...). In the armpits, a higher pH leads to colonization by certain resident bacteria that produce odors, such as propionic bacteria and staphylococci. Therefore, deodorants containing citrates reduce the pH and inhibit bacterial activity;

  • Skin Type : Indeed, teenagers with oily and acne-prone skin tend to have a more alkaline skin pH.

  • Gender : Due to a higher sweat production, men have a more acidic skin pH than women.

  • Skin Pigmentation : Studies have proven that darker skin tones have a more acidic skin pH than lighter skin tones. This is due to the higher presence of epidermal lipids, specifically fatty acids, which result in a lower pH and better integrity of the barrier function.

When skin pH and enlarged pores are correlated.

Several studies have highlighted the connection between skin pH and acne. Now, enlarged pores are one of the physical manifestations of acne. Therefore, it can be said that a change in the skin's pH may be linked to the dilation of pores.

A 2017 study compared the skin pH of subjects with acne and those without. The majority of acne cases had a high skin pH. The average pH of these cases was higher than the normal reference value (pH 4.5-5.5 for women, 4-5.5 for men) and that of the control subjects.

Thus, the increase in facial skin pH in patients with acne under basal conditions reflects a chronic state of instability in the stratum corneum, which could predispose individuals to the onset and/or recurrence of acne. This could be a common area through which traditional pathomechanisms might act in acne. The integration of measures aimed at maintaining the pH of the stratum corneum during treatment could prove useful, hence the use of certain acidic molecules such as retinoids.

Furthermore, the bactericidal activity, due to dermcidin and nitrites present in sweat, is optimal at a pH of 5.5. When the skin's pH increases, the resident bacterial flora undergoes a change: the colonization and activity of P. acnes and Staphylococcus aureus increase while the action of antimicrobial peptides decreases, predisposing the epithelium to vulgar acne.

Finally, regarding the sebum produced by the sebaceous glands, it is observed that it has a reduced content of free fatty acids, which play a role in the acid mantle that covers the skin. The resulting effect could be unfavorable on the skin's pH, making it more basic.

Sources:

  • Chaitra Prakash & al., Skin Surface pH in Acne Vulgaris: Insights from an Observational Study and Review of the Literature, J Clin Aesthet Dermatol. (2017)

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

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