The Importance of pH Value in Skin Care

The pH values of cosmetic products we frequently use in our daily lives are as important as the components they contain. Recent research indicates that the skin's natural pH value is in the range of 4-5. At birth, newborn skin has a pH of approximately 6.4 and reaches its normal skin pH within 4 days, which it will maintain for most of its life. In elderly individuals, skin pH reaches neutral values (approximately pH=7) [1,2]. When skin pH is elevated, the skin's natural barrier layer deteriorates due to the high pH, and problems such as dryness, irritation, chafing, infection, etc. begin to occur. To support the skin's natural barrier layer and regulate bacterial flora, cosmetic products with pH values between 4-5 should be used [2]. The acidic nature of the skin surface was first determined by Heuss in 1892 [3]. In 1928, Schade and Marchionini more definitively demonstrated through experiments using biophysical methods that the skin surface has an acidic nature [4]. The skin surface's acid pH, known as the acid mantle, and the pH gradient of the stratum corneum regulate epidermal functions such as antimicrobial barrier, permeability barrier, barrier integrity and cohesion [2]. At birth, skin pH in newborns is approximately 6.4 on average, and it takes approximately 4 days for this value to reach 4.9, the skin's normal acidic pH [1]. Studies have found that the acidic pH of the stratum corneum prevents the proliferation of pathogenic microorganisms (such as Staphylococcus aureus and Malassezia) [5]. The effect of pH on the adhesion of resident skin microflora to the skin has been evaluated. An acidic skin pH (4-5) supports the skin's natural bacterial flora, while alkaline pH (8-9) has negative effects on this flora [6]. Additionally, pH has been found to affect skin barrier function, lipid synthesis and aggregation, epidermal differentiation and desquamation [5]. As in adults, in newborn skin, external factors such as soaps and detergents, but more importantly cosmetic or topical medical products applied to the skin and not rinsed off, can alter skin surface pH. Even the use of water or a mild detergent solution can cause a sudden increase in skin pH, and the skin pH does not return to normal levels for 6 hours after washing [5]. If skin pH shifts from acidic to neutral, there is an increase in the total number and types of bacteria, altering skin microflora. Staphylococcus aureus shows optimal growth at pH 7.5, while Propionibacterium acnes shows optimal growth at pH 6.3. When skin pH increases, the growth of these bacteria leads to atopic dermatitis (allergic eczema) problems. In atopic dermatitis, elevated pH causes deterioration of epidermal lipid lamellae and consequently impaired barrier function. With impaired barrier function, water loss from the skin increases and skin moisture decreases. Deterioration of the skin's barrier layer causes irritant substances to penetrate the skin more easily, resulting in irritation, chafing and other skin problems [5]. Additionally, elevation of skin pH has been reported to play a role in the pathogenesis of skin diseases such as irritant contact dermatitis, ichthyosis, acne vulgaris and Candida albicans infections. In diaper dermatitis (diaper rash), commonly known as prickly heat among the general public, a number of factors play a role including prolonged exposure to urine and feces, increased hydration, changes in skin microbial flora and altered skin pH. As pH increases, the Candida albicans yeast proliferates in the area, causing irritation, chafing and infection problems. For this reason, the pH value of skin cleansing products (wipes, shampoo, shower gel, etc.) and care products (lotion, cream, ointment, etc.) being approximately between 4-5 plays an important role in preventing and treating these skin problems. By applying products with low pH values to the skin and reducing skin pH to between 4-5, the skin's natural barrier layer is supported and contributes to creating a healthier skin environment.

References: [1] Basic Newborn Care, Directorate General of Public Health. [2] Jürgen Blaak, Rainer Wohlfart, Nanna Y. Schürer: Treatment of Aged Skin with a pH 4 Skin Care Product Normalizes Increased Skin Surface pH and Improves Barrier Function: Results of a Pilot Study. Journal of Cosmetics, Dermatological Sciences and Applications, 2011, 1, 50-58. [3] Heuss E: Die Reaktion des Schweisses beim gesunden Menschen. Monatschr Prakt Dermatol 1892; 14:341-343. [4] Schade H, Marchionini A: Der Säuremantel der Haut (nach Gaskettenmessung). Klin Wochenschr 1928; 7:12-14. [5] Ehrhardt Proksch: pH in nature, humans and skin. Journal of Dermatology, University of Kiel, Kiel, Germany, 2018, 1-9. [6] H. Lambers, S. Piessens, A. Bloem, H. Pronk, P. Finkel: Natural skin surface pH is on average below 5, which is beneficial for its resident flora. International Journal of Cosmetic Science, 2006, 28, 359-370..

Caner Acar Specialist, Cosmetics R&D Specialist Eczacıbaşı Consumer Products Manufacturing and Trading Inc.