Research has shown the importance of skin surface pH in maintaining skin balance (i.e. homeostasis), barrier function, and antimicrobial defense. A comprehensive review by Ali and Yosipovitch (2013) clarifies the relationship between pH and various skin processes and skin conditions.
The Acid Mantle
The concept of the "acid mantle," first introduced by Schade and Marchionini in the 1920s, has gained renewed significance in light of recent research. The stratum corneum typically maintains an acidic pH between 4.0-6.0. This should be compared to the near-neutral pH of underlying skin tissues. This acidic microenvironment is crucial for:
Lipid Balance: Skin cells are held together by a lipid membrane. Key lipid-processing enzymes, vital for synthesis of fatty molecules or lipids, have optimal activity at acidic pH levels.
Stratum Corneum Integrity: Serine proteases, involved in skin shedding, are pH-dependent. An increase in pH can lead to excessive protease activity (and excessive shedding), compromising the stratum corneum. Too much protease activity can also lead to wounds that don't heal.
Antimicrobial Defense: The acidic environment inhibits colonization by pathogenic bacteria while supporting the growth of beneficial flora.
Internal Factors
Several internal factors affect skin pH, including age, skin site and pigmentation.
Age: Newborns exhibit higher skin pH, which gradually acidifies over the first month of life. Older adults also show increased skin pH and reduced buffering capacity.
Anatomical Site: Areas where the skin folds typically have higher pH levels, potentially explaining the predisposition to certain infections in these areas.
Skin Pigmentation: Generally, darker skin types demonstrate lower pH levels, correlating with enhanced barrier function and stratum corneum integrity.
pH Alterations in Skin Conditions
The review highlights several skin disorders characterized by pH abnormalities. Two examples are:
Atopic Dermatitis (AD) or Eczema: Patients with eczema exhibit higher skin pH in both lesional and non-lesional skin. This may contribute to increased serine protease activity, compromised barrier function, and enhanced colonization by pathogens.
Acne: The growth of P. acnes (a bacteria associated with acne) is optimal at a pH between 6-6.5 and reduced at pH values below 6, suggesting a role for pH related treatment for acne patients.
Clinical Implications and Future Directions
The authors emphasize the importance of considering skin pH in clinical practice, particularly in selecting appropriate cleansers and topical treatments. They advocate for the use of gentle, soap-free cleansers with pH values close to skin pH (4.5-6.5), over traditional alkaline soaps.
Furthermore, the potential therapeutic role of topical products in various skin conditions warrants further investigation. Preliminary studies using acidic solutions have shown promising results in improving barrier function and reducing inflammation in conditions like eczema.
This review underscores the multifaceted role of skin pH. As our understanding of skin acidity deepens, it may lead to novel therapeutic approaches and optimized skincare regimens for both healthy and diseased skin.