THE EFFECT OF pH ON SKIN

Maintenance of skin pH is essential to the health and normal functioning of the skin. Where there are elevations in the skin pH, there are unfavorable outcomes such as impairments of a permeability barrier homeostasis, decreased skin integrity, cohesion, and increased susceptibility to microbial infections. Alterations in these skin functionalities play a known role in the pathogenesis and clinical manifestations of skin disease.

Impaired Permeability Barrier Homeostasis

The pH of cutaneous epithelial cells, particularly within the SC, largely influences the physical, chemical, and microbial protection properties of the skin. Furthermore, an acidic pH is critical for permeability barrier homeostasis, in part because of two key lipid-processing enzymes: ß-glucocerebrosidase and acid sphingomyelinase. These proteins generate a family of ceramides from glucosylceramide and sphingomyelin precursors and exhibit low pH optima. Increased skin pH results in defective lipid processing and delayed maturation of lamellar membranes. These lipids from multi-lamellar sheets amidst the intracellular spaces of the SC are critical to the SC’s mechanical and cohesive properties. This enables the SC to function as an effective water barrier. Altered pH environments have been shown to affect not only lipid content but also lipid organization and intercellular lipid lamellae (ICLL) resulting in an impaired skin barrier. Impaired barrier function allows easier penetration of topically applied products and delays barrier recovery after injury or insult to the skin and can trigger the onset of inflammatory skin diseases.

Decreased Skin Integrity and Cohesion

Experimentation has shown that in a neutral pH environment, there is an enhanced tendency for the tape stripping to remove the SC, a demonstration of compromised skin integrity and cohesion. The reduced SC integrity and cohesion seen with alterations in pH may be partially related to a pH-dependent activation of the serine proteases that exhibit neutral pH optima. The literature supports that serine proteases are activated in environments of increased pH such as in inflammatory skin conditions, newborn and elderly individuals, and type I-II skin. Their activation leads to the premature degradation of corneodesmosomes, and hence increased desquamation, resulting in loss of integrity and cohesion.

Increased Susceptibility to Skin Infections

The acidic pH of the SC restricts colonization by pathogenic flora and encourages the persistence of normal microbial flora. Pertinently, newborn and elderly skin, intertriginous areas, and chronically inflamed skin display an increased skin pH and hence reduced resistance to pathogens. Higher pH (decreased acidity) and impaired buffering capacity predispose to infection and skin disease.

In Summary, increased skin pH can lead to abnormalities in the SC integrity/cohesion, permeability barrier homeostasis, pathogen resistance, and immune function. These abnormalities areattributable to the pH-mediated increase in the serine protease-mediated degradation of corneodesmosomes, defect in lipid processing, and decrease in antibacterial activity, respectively.

Now that we have a better understanding of the importance of maintaining tightly regulated skin pH, we can start to divulge the mechanisms behind skin acidification and buffering capacity.