“Nature has provided our skin with an acidic mantle. We would do well to protect this crucial aspect of skin health by avoiding exposure to common daily stressors (e.g. harsh alkaline soaps and solvents). Personal care strategies that add back some acid tonic may well help us maintain more optimum skin surface health.”
Healthy Skin - Our Outer Protection
The skin is a vast physical barrier at our interface with the external environment and so is designed to protect us against desiccation, and mechanical, chemical and microbial insults. However, it is not an inert defensive barrier; we increasingly learn that even its outer hardened layers are extremely active biochemically. The skin’s supply of sweat and sebum and other entities help maintain a healthy skin surface, not least by regulating its pH.
Skin pH - Protect With Skincare Routine
It is reported that the acidic nature of the skin’s surface is unique to humans, and that at least for specific body site the pH of the skin surface in males is similar to that in females. Although the nature of the skin’s ‘acid mantle’ was described as early as 1928, there are still significant gaps in our knowledge of where this acidity originates from.
pH is most commonly measured on the skin surface and there can be up to 3 pH units difference between the more neutral pH environment (pH 7.4) of the living cell layers of the skin [dermis] compared to the hardened barrier surface [epidermis] (i.e., between pH 4,0 and 5,0). It is this value that we must work to protect with our skincare routines.
A large number of sources contribute to the acidity of the skin surface including; lactic acid (an alpha hydroxyl acid) and free amino acids from sweat, free fatty acids from sebum, and free fatty acids from epidermal phospholipids. In addition, amino acids and other acids derived from cell maturation events are also involved; the latter include natural moisturising molecules. Sweat and sebum contain vital components for a healthy skin.
Acid pH as a Protection Against Microbial Overgrowth
The importance of an acid pH skin surface can be seen in the context of regulating unfriendly bacteria. Indeed, a significant anti-microbial defence can be afforded by the acidic pH of free fatty acids of the stratum corneum. The metabolites of skin microflora can further contribute to the acidification of the skin surface. It is comforting to note that ‘friendly’ skin microbes (e.g., micrococci) tend to like the acidic pH while ‘enemy’ microbes (e.g., staphylococci) prefer neutral/basic conditions. The ‘normal’ bacterium associated with acne (Propiobacterium acnes) prefers a pH microenvironment closer to the neutral [7,2].
Nutrition and skin pH
Skin disorders have been long associated with nutritional deficiencies. Essential fatty acids can consist of up to 30% of the skin’s supply of fatty acids, and so may have a considerable impact on skin pH.
Hygiene and skin pH
Personal care habits may have a profound effect on skin pH. Simply rinsing the skin with water causes an immediate but transient increase in skin pH. Moreover, washing hands in standard soaps can increase skin pH by as much as three units to pH 8 – clearly in the alkaline part of the pH range.
• It can take an hour or more before the skin’s pH returns to normal after washing with standard soap. The relatively common occurrence of dermatitis in the general population has implications for skin cleansing and skin care strategies.
• The use of acidic topical skin care products is likely to have beneficial effects for both skin dryness and dermatitis, and reduce further sensitivity (including prophylactically) to contact irritants.
Age and pH
It is thought that the pH buffering capacity of the skin may decrease with age. This may explain the increased sensitivity to the skin to contact irritants, cleansing agents and also bacterial infections in the elderly.
Bio-rhythms and Skin pH
The skin alters its pH at different times of the day due mainly to associated changes in skin enzyme activity, especially in the stratum corneum.
• The skin is more alkaline in the afternoon than at night.
• There are also seasonal variations in skin pH (as well as in temperature, water loss and surface lipid levels).
• Skin pH can be significantly lower in July compare to January, April or October. These observations may be explained by the lowering of pH by sweat-associated acidity (highest during summer).
• These patterns have important implications for your skincare routine.
pH in Skin Health and Disease
Studies have shown that recovery of skin barrier function after injury (e.g., from abrasion or solvent exposure) is faster if the skin exposed to solutions of pH 5.5 rather than neutral solutions of 7.2.
To learn more, read Professor Desmond Tobin’s Paper at yinyangskincare.co.uk
References
Tobin DJ. Biochemistry of human skin – our brain on the outside. Chemical Society Reviews. 35(1): 52-67, 2006.
Zlotogorski A. Distribution of skin surface pH on the forehead and cheek of adults. Arch Dermatol Research 279:398-401, 1987.
Rippke F, Schreiner V, Schwanitz HJ. The acidic milieu of the horny layer: new findings on the physiology and pathophysiology of skin pH. American Journal of Clinical Dermatology 3(4):261-72, 2002.
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