What is commonly called the acid mantle of the skin is not a myth. It is an essential part of overall health. Anyone who has ever suffered the tight dry feeling of their skin when they wash with too strong a soap knows what it means to strip away their acid mantle. The mantle is maintained by natural body oils and perspiration. Skin that has lost the slightly acidic coat is not only prone to dryness, itchiness and wrinkling, it is also very vulnerable to infection. Some topical lotions are sold to replace or maintain this mantle, but good health, including proper diet with healthy plant oils, exercise and a clean active lymph system may also keep the skin much healthier and younger looking by giving the body what it needs to maintain its natural acid mantle.
The following article may be a little too scholarly for some, but it does explain the basic idea in depth:
The Skin’s Acid Mantle
"Much More than a Surface Phenomena"
Paul Thau, PaCar Tech
Since the early part of the last century, scientists have known that the outer layers of the skin were acidic. The physiological pH of healthy skin has an average value between 4.5 and 5.9. In 1928 Schade and Macrhionini reported the acidity of skin, termed as the “Acid Mantle”, helped to ward off infections by preventing the growth of bacteria and fungi. But the source of all this acid and how it helped to maintain the skin’s strength and integrity, remained a mystery. (1)
The skin’s protective acid mantle is also referred to as the hydrolipid film.
The oily phase or liposoluble phase originates in the sebaceous gland closely attached to the hair follicles, and the epidermic lipids of the bilayers of the stratum corneum. The aqueous phase or hydrosoluble phase is made up by the Natural Moisturizing Factors (N.M.F.) and perspiration from the eccrine sweat glands covering the entire skins surface.
Some of the identified components of the protective acid mantle are:
• lactic acid and various amino acids from eccrine glands
• free fatty acids from sebum
• amino acids, pyrrolidine carboxylic acid and urocanic acid from the cornification process
• water from the deepest layers that has reached the skin
Today, all the factors regulating skin surface pH are still unknown. However, there is sufficient evidence to support the barrier function and self-disinfection of the skin’s acid mantle. The pH value of human acid mantle is generally within a range from 4 to 6. On the other hand, the body’s internal pH is about neutral, ranging from about 7.35 to about 7.46. Skin pH varies among different body areas and also depends on the skin moisture content—skin areas with higher moisture having a higher pH.
The function of the protective acid mantle was initially focused on indirect microbiological defense and the direct protection against external alkaline challenges. This classical knowledge of the skin’s acid mantle has since been given expanded dimensions by more recent dermatological, biochemical and molecular biological studies.
A central role for the acidic milieu as a regulating factor in stratum corneum homeostasis has been emerging. It has relevance to the integrity of the barrier function, from normal maturation of the stratum corneum lipids through desquamation. Changes in the pH and the physiological conditions influencing it appear to be involved not only in the pathogenesis, prevention and treatment of irritant contact dermatitis, but also of atopic dermatitis and in wound healing.(1)
Recent research findings have revealed that an acid environment is important for the following:
• activation of the enzymes responsible for the synthesis of epidermal lipids
• formation of the lipid membrane
• restoration of the horny layer following mechanical or chemical damage
The stratum corneum is able to signal the epidermis when barrier function is disrupted and to maintain a 100-fold difference in hydrogen ion activity (2 pH units) compared to the epidermis. This is a remarkable activity in a dead tissue only 15-20 microns thick.
An essential protective mechanism of the skin’s acid mantle is its alkali-neutralizing capacity. To counteract the influence of alkaline substances, the protective acid mantle uses inherent buffer substances. These neutralize alkaline agents and ensure that the acidic milieu is restored and stabilized.
The pH of the skin follows a sharp gradient across the stratum corneum which is suspected to play an important role in controlling the enzymatic activities involved in cellular metabolism and renewal The gradient is maintained by several systems, such as sweat, sebum secretions and degradation as well as cellular metabolism.(2)
Various reports have shown that skin alkalinization has negative effects, such as irritant dermatitis and atopic skin disease. Infant skin pH for the two weeks after birth is close to neutral. For this reason, the newborn skin’s ability to control growth of microorganisms is low and may have low resistance to infection. Other reports have claimed that an increase in skin pH is an important contributing factor in diaper dermatitis. A recent study correlated skin pH with the severity of experimentally induced irritant dermatitis. It has been found that high skin pH coincides with high transepidermal water loss, which is one of the more sensitive parameters used to quantify an irritant response in the skin.(3)
Studies have shown that rinsing the skin with water alone immediately produces a transient increase in skin pH, and washing the hands with toilet soap causes the pH on the palms of the hands to increase by an average of 3 units. This increased skin pH was not completely normalized 90 minutes after washing with soap. Acidic pH syndets, such as sodium cocoyl isethionate are now preferred for skin cleansing in patients with seborrhoic-type skin conditions because of their bacteria-regulating properties and favorable skin compatibility profile.(4,5)
Disturbances of the skin pH have been implicated in the development of primary irritant diaper dermatitis. As a preventative measure, it has been recommended by researchers to create a milieu in the diaper area that minimizes moisture as well as elevated pH. Recent studies have demonstrated the regulating effects of acid cleaning wipes on the pH in the diaper area, and the use of acid syndets results in a significantly smaller pH increase compared to alkaline soap in infants and small children.(6)
The use of acidic topical preparations containing alpha hydroxy acids, such as lactic and glycolic acid, for kereatolysis has proved effective in clinical practice. The treatment of atopic dermatitis is aided by their pH regulating properties.
The U.S. Patent abstract below is based upon some of the above findings.United States Patent 6,352,700 Lotionized tissue products containing a pH balance compound for the skin (Assignee: Fort James Corporation).
Abstract: A substrate treated with a lotion including a skin pH balancing compound and a base lotion. The pH-balancing compound is preferably an organic acid, such as an alpha-hydroxy acid, an alpha-dihydroxy acid, or a beta-hydroxyacid, a combination of an organic acid and a salt of an organic acid, or a buffer combination, such as combinations of citric acid
and disodium phosphate, or disodium citrate and sodium hydroxide. The preferred lotion has the effect of maintaining the skin acid mantle while making the treated substrate, preferably tissue, towel or napkin, optionally wet-strengthened, wipe or nonwoven material, feel smooth, lubricious and nongreasy. The skin care benefits of the lotionized substrate are expressed whether the product is used dry or prewetted with water.
An example of a classic pharmaceutical acid mantle vehicle and skin treatment cream is shown below:
Acid Mantle Cream®- Bradley Pharmaceutical
Claims: Restores and maintains protective acidity of the skin. Relieves mild skin irritation. Soothes diaper rash, dry scaly skin. Apply several times daily, especially after wet work.
Ingredients: Water, Cetearyl Alcohol, Sodium Lauryl Sulfate, Sodium Cetearyl Sulfate, Petrolatum, Glycerin, Synthetic Beeswax, Mineral Oil, Methylparaben, Aluminum Sulfate, Calcium Acetate, White Potato Dextrin
Conclusion: An intact acid mantle biologically prevents inflammation and irritation to the skin. This fact provides the cosmetic formulator with a strong rationale to make appropriate raw material and formulation decisions to maintain this protective milieu. Numerous studies, particularly on individuals with various dermatological conditions, have demonstrated the merits of cleansing and treatment products developed with minimum disturbance of the acid mantle as one of the parameters.