The pH plays a vital physiological role in nature as well as in humans. The pH varies from 1 to 8 in human organs with tight regulations in blood and epithelia of barrier organs. The physiological pH of the stratum corneum (the skin surface) ranges from 4.1 to 5.8. The stratum corneum is the outermost layer of the epidermis, and it consists of dead cells. It serves as the primary barrier between the body and the environment. This pH range of the stratum corneum signifies most of our body parts are acidic.
The chin has the highest pH of 5.6. Areas such as the forehead and the upper eyelid have the most acidic pH ranges of 4.4 and 4.6, respectively. Meanwhile, the volar forearm, nose, neck, nasolabial fold, cheek, and perioral area have a pH between 4.4 and 4.6. The remaining body parts like the axillae, groin, the toes have pH values of 6.1 and 7.4. Studies have shown that the areas with a high pH value are more likely to be infected and display eczematous reactions. In simple terms, a pH greater than 5.9 is responsible for smelling fit as bacteria are more likely to live in those areas.
Many factors determine the pH of the skin, filaggrin degradation, fatty acid content, sodium-hydrogen exchanger (NHE1) activation, and melanosome release.
Studies have shown that the acidic pH of the stratum corneum serves as an antimicrobial barrier preventing colonization of microorganisms. The skin pH influences the skin barrier functions such as lip synthesis and aggregation, epidermal differentiation, and desquamation. Desquamation means the shedding of the skin. Desquamation usually occurs every 28 days. In darkly pigmented individuals, desquamation occurs more rapidly. The rapidity of desquamation can lead to skin discoloration, vitiligo, and so on.
A disruption of the physical barrier leads to an increase in pH level. Inflammatory skin diseases or diseases involving the epidermis exhibit a disturbed skin barrier by increasing the skin pH, leading to atopic dermatitis, irritant contact dermatitis, ichthyosis, rosacea and acne, and aged and dry skin. The process of acidification normalizes the skin pH. It establishes a physiological microbiota to repair the skin barrier and induce epidermal differentiation and reducing inflammation.
The pH level of healthy skin
Inflammatory skin diseases involving the epidermis exhibit an increased pH. People who suffer from inflammatory skin diseases have an increased pH of 0.2 and 0.3 units. An increase of 0.3 pH units means half of the concentration of H+-ions, which significantly influences biochemical processes leading to eczema, dermatitis, and radiodermatitis. People with dry and sensitive skin also have a skin pH that has been increased by 0.3 to 0.4 in units.
Racial differences also play a vital role in the skin pH level. Studies have shown that darkly pigmented skin has a lower pH than its lightly pigmented counterparts. The average Black skin pH is about 4.6, whereas the average white skin pH is 5.0. The same study also found that darkly pigmented skin tends to have a superior skin surface (SC) integrity and barrier function than their light pigmented counterpart.
pH and Antimicrobial Effects
The pH level of the skin surface has a vital role in antimicrobial activity, barrier function, and desquamation. The acidic pH inhibits the colonization of photogenic bacteria.
Reducing skin pH as a therapeutic tool to combat skin diseases caused by inflammation
Acidification has been used for decades to treat wounds. Similarly, acidification can potentially combat acne, eczema, dryness, and other inflammatory skin diseases.
The acidic environment alters the protease activity. It releases oxygen, reducing toxicity, bacterial end products, enhancing epithelization and angiogenesis. Most of the pathogenic bacteria associated with infected skin wounds need a pH value of more than 6, while their growth inhibits at a lower pH value.
Skincare products developed to fight skin diseases tend to have adjusted pH of 5, 5.4, or 5.4, which aimed to preserve the “physiological” skin pH. Skincare products with an adjusted ph of 4.0 may successfully treat acne. The best pH level for skincare products intended for darkly pigmented consumers should be between 4.0 to 5.5.
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Acidification has been used for decades to treat wounds. Similarly, acidification can potentially combat acne, eczema, dryness, and other inflammatory skin diseases.