Skin pH And Why it's Important

Skin pH has been recognised as an important factor and has been investigated for almost a century, ever since the term "acid mantle" was used by Heinrich Schade and Alfred Marchionini in 1928.

Nevertheless, skin pH continues to be researched by the scientific community. Recent decades were marked with comprehensive research of different skin components, mechanisms and processes, relating to either healthy or diseased skin. Collected data provide new and/or better insight into skin characteristics. Among others, acidic pH of the skin surface has been recognised as a regulating factor for the maintenance of the stratum corneum homeostasis and barrier permeability.

From the beginning of its investigation, skin surface was considered to have an acidic nature. Older publications, generally recognised, suggested that skin pH (forearm, adult male) ranges from 5.4 to 5.9. More recent studies have found that the skin pH is even more acidic, and today it is accepted that the pH of the skin ranges from 4.1 to 5.8, depending on the body part. Exceptions are found in certain regions—in certain physiological gaps (axillae, groin, toe interdigits and anus), the pH values range from 6.1 to 7.4. All of the mentioned results were obtained by potentiometric methods, with the use of flat glass electrodes. Due to the measuring principle that only takes into account water-soluble components, some authors believe the actual skin pH could be closer to 6, with some more acidic microdomains.

Considering the importance of the pH in human physiology and pathology, it is equally relevant for each human organ to resist acid/alkaline aggression (maintain specific pH) to some extent, or in other words to possess a buffer system. The skin’s buffering capacity has been investigated earlier and separately from the skin pH maintenance mechanisms, despite the fact that reliable data suggest certain co-dependence in those processes. Existing data accredit free amino acids of the epidermis (originating from eccrine sweat, degradation of skin proteins and hair follicles) to be crucial Stratum Corneum (SC) components for the neutralisation capacity of the skin. Other investigated components of the SC, such as sebum, keratin and CO₂, although without a significant buffering role, still seem to have certain functions in the protection of skin from acids and bases.

Obviously, different endogenous and exogenous factors affect skin pH. Besides the anatomic site and genetic predisposition, age and ethnicity are the most thoroughly investigated endogenous factors. At birth, skin pH is higher, i.e., near neutral, and within 4 weeks, it reaches the physiological value, and usually remains as such until the end of the fifth decade of life.

The maintenance and the protection of the normal/physiological skin pH is a very important task. As acknowledged, extrinsic factors affect skin pH, and topically applied products have to be recognised as administrators of this task. Cosmetics, due to their extensive everyday usage could contribute to skin health maintenance, via skin pH value control. Additionally, in certain skin disorders, the use of topical products which could correct skin pH should be a part of the therapeutic regimen. Keeping this in mind, the pH of any topically applied product together with its buffering capacity must be considered carefully.

Although the use of soap as a cleansing agent is a part of human history, foundations in contemporary skin cleansing were set at the beginning of the 20th century with the development of different synthetic substances.

At the same time, with the expansion of cleansing products, dermatologists have become aware that the use of soaps could deteriorate the condition of existing dermatoses (various skin conditions). In fact, pioneering studies and the first data on the influence of cosmetic products on the skin surface pH concerned the effect of skin cleansing products. Soaps, while exerting their cleansing function, these substances can negatively affect the structural and functional integrity of the skin. Their damaging effects are the result of an increase in the skin surface pH (alkalisation), excessive removal of skin structural components (lipids and proteins), stratum corneum damage and even cytotoxicity. Their skin-irritation activity is related to interactions with skin components and depends on the surfactant’s structure and physical properties in aqueous solutions

It is a generally accepted fact that an extensive washing with alkaline soaps will lead to skin barrier impairment with a concomitant pH increase in any skin condition. Although the surfactants are deemed responsible for the skin irritation effect of the pertaining cleansers, it is shown that poor rinsability in combination with high pH may also increase the irritation potential of a product. The use of a skin cleanser or even tap water will induce a short-term skin pH increase, but its duration depends on skin condition, frequency of washing and the composition of the cleansing product (surfactant/s, additives and the product’s pH). Therefore, every skin cleanser is a potential skin surface modifier and the pH of this product must be adjusted to a physiological pH during its development.

Acidic skin cleansers should be used for frequent washing, by consumers with sensitive skin and different skin conditions and disorders related to a skin pH increase. In order to accomplish an acidic pH of the product, skin cleansers are formulated with syndets (synthetic detergents), which have an acidic pH close to the skin’s pH. If the formulation needs a pH adjustment and/or stabilisation, frequently used ingredients are Lactic and Citric Acid, Sodium Acetate, Sodium Lactate, Sodium Citrate, Diammonium Citrate, etc. Acidic skin cleansers for normal, oily and acne-prone skin often contain acidic active ingredients, with Hydroxy Acids (Salicylic Acid, Glycolic Acid, Lactic Acid, Mandelic Acid, etc.), Ascorbic Acid, Ferulic Acid and Linoleic Acid being the most common.

Skin care products aim at keeping or improving good condition/appearance of the skin. This is accomplished with the use of vehicles/carriers, which are mostly emulsions—creams, lotions or serums—intended to deliver product compounds to the skin. Scientific interest for emulsions is tremendous and researchers from various fields are engaged in their investigation. Nevertheless, research on skin care products’ pH in relation to skin surface pH is relatively new. Interrelation between product and skin surface pH is a complex issue with ambiguous interpretation of the obtained results.

During our entire life, the skin is exposed to hostile influence of external and internal factors and their interactions with each other, finally resulting in skin aging. Therefore, the imperative in skin care became the prevention and reduction of signs of aging. Gathered information about the skin structure and functions together with the knowledge of the skin exosomes enabled the development of new topical product strategies. Nowadays, terminology used in cosmetic marketing campaigns avoids terms related to skin aging. Terms such as ‘aged skin’, ‘wrinkles’, ‘old’, etc., have been replaced with terms related to strength, youthfulness and skin wellbeing. Similar to this, ‘anti-age’ cosmetics has shifted to a category of cosmetics used for skin health maintenance.

Not my own work. Taken from (and for more information):

Lukić, M.; Pantelić, I.; Savić, S.D. Towards Optimal pH of the Skin and Topical Formulations: From the Current State of the Art to Tailored Products. Cosmetics 2021, 8, 69. https://doi.org/10.3390/cosmetics8030069

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