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The Importance of Skin pH

Gil Yosipovitch, MD, and Judy Hu, MD

Excerpted and adapted with permission from HMP Communications.
Yosipovitch G, Hu J. The importance of skin pH. Skin & aging 2003; 11(3):88-93. Copyright 2003 HMP Communications

It’s well known that the skin is the first line of defense against all elements, such as microorganisms, wind, and pollutants. And it’s the acid mantle, a fine film with a slightly acidic pH on the surface of the skin that provides protection for the skin. It plays a very important role as an integral part of the barrier function of the stratum corneum. Recent studies have demonstrated that increased enzyme activity of phospholipase A2 is related to the formation of the acid mantle in the stratum corneum. This combination makes the sin less permeable to water and other polar compounds. It also contributes to the low pH of the skin surface. Normal skin surface pH is between 4 and 6.5 in healthy people, though it varies among the different areas of the skin.

Newborn infants do have a higher skin surface pH compared to adults, but this normalizes within three days. It’s important to protect the stratum corneum because if it’s damaged, skin surface pH has been shown to increase, creating susceptibility to bacterial skin infections or skin damage and disease.

Providing Protection

The acid mantle protects the skin from bacterial and fungal infections. The acid mantle contains lactic acid and various amino acids from sweat, free fatty acids from sebum, and amino acids and pyrrolidine carboxylic acid from the cornification process of skin.

The acid mantle:
• Supports the formation and maturation of epidermal lipids and therefore the maintenance of the barrier function
• Provides indirect protection against invasion by microorganisms
• Provides direct protection against alkaline substances (alkali neutralizing capacity)

If the acid mantle becomes disrupted or damaged, or loses its acidity, the skin becomes more prone to damage and infection. Washing skin with soaps or detergents can cause the loss of acid mantle. Repetitive washing alters the stratum corneum and barrier functions, including the pH of skin surface. Once damaged, it can take up to 14 hours to restore, by which time, it’s most likely under assault again from another washing. Most people wash their hands about three times a day, on average. Single washings shift pH to the alkaline region, which can shift back to normal within a few hours.

Other Factors that Affect pH

There are many diseases that cause an increase in skin surface pH. Skin conditions that can cause this phenomenon include:
• Eczema
• Contact dermatitis
• Atopic dermatitis
• Dry skin

Acute eczema with erosion can cause skin surface pH to shift from normal to 7.3 to 7.4. This is a 1,000- fold increase in the pH shift, as pH is measured in logarithmic function. The entire skin surface pH is increased on skin of people with atopic dermatitis. An increased skin pH contributes to Staphylococcus aureus colonization, which can play a role in the genesis of atopic dermatitis, discoid eczema, and infective dermatitis as a superantigen.

Systemic diseases that can cause an increase in skin surface pH include:
• Diabetes
• Chronic renal failure
• Cerebrovascular disease

The explanation for the elevated pH in these diseases is not clear but is possibly related to low levels of phospholipase and to autonomic dysfunction causing abnormal sweat secretion. An increase in skin surface pH encourages bacterial growth. Patients with diabetes have an increase in skin surface pH in intertriginous areas, and it’s known that patients with diabetes are more prone to Candidal infections, especially in intertriginous areas. Studies have shown that Candidal skin lesions are more pronounced on skin with higher pH values, possibly due to a pH dependence of the yeast’s virulence capacity and/ or a modulation of the host defense capacity.

C.albicans is dimorphic, and an acidic pH favors the blastospore form, while an increased pH favors the hyphael form. The hyphael form of Candida is the initial invader that grows best at pH>6.5, and patients with diabetes have a decreased level of skin lactic acid. The use of skin occlusive products, such as dressings and diapers, are known to raise skin pH and are associated with skin infections caused by C. albicans.

Products to Use to Maintain pH Levels

There are three main categories of cleansing agents:

• Soaps
• Synthetic detergents
• Lipid- free cleansing agents

It’s been shown that soaps make the skin more alkaline than synthetic detergents. The irritancy potential of cleansing agents is dependent on a number of factors, which include pH, and soaps are known to increase skin surface pH. Acidic cleansers are less irritating than neutral or alkaline ones, and people prone to dry skin are advised to use acidic cleansers. Agents with slightly acidic or neutral pH, nonionic surfactants, may be preferable for patients who are at increased risk for irritating skin reactions. Therefore, advise patients with skin conditions to choose a mild cleaning agent with a low pH. Even minor differences in the pH of skin cleansing preparations can be important to the integrity of the skin surface. This should be taken into account when determining the optimal soap.

What’s Really on the Market

Since the effectiveness of low pH soaps and cleansers has been well documented, one would think that companies producing home care products in this fashion. However, the market in the United States carries very low- pH soaps and cleansers. Unless we, as clinicians, educate our patients about the importance of low- pH cleansers and what’s available, they won’t know to look beyond the most common soaps on the market. Most cleansers in the United States, with a few exceptions, are at a pH of 9.5 to 10.5. This pH is inherent to the formula, which is a sodium soap of fatty acids. The formulas that have a neutral pH are called “ syndet.” Chemically, they are not soaps, but a synthetic detergent in a bar form (thus their names).


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