The pH level of a cleanser determines its acidity or alkalinity, significantly impacting the health and integrity of human skin. Cleansing products are not all chemically the same, and the difference in pH affects the skin’s natural protective layer. Understanding this distinction is fundamental to choosing products that support the skin’s barrier function.
Understanding pH and the Skin’s Acid Mantle
The measure of acidity or alkalinity is known as pH, or “potential of hydrogen.” It is determined using a logarithmic scale ranging from 0 to 14. A pH of 7 is considered neutral; numbers below 7 indicate increasing acidity, and numbers above 7 denote increasing alkalinity.
The skin’s outermost layer is covered by a protective film known as the acid mantle, composed of sebum, sweat, amino acids, and fatty acids. This film maintains a naturally slightly acidic environment, typically pH 4.5 to 5.5, with some research suggesting an optimal pH closer to 4.7. This acidity is a defense mechanism that helps manage the skin’s microbial balance and supports the skin barrier’s structural integrity.
The slightly acidic environment is crucial for the optimal activity of enzymes that produce and process the lipids and proteins forming the skin barrier. This low pH also creates an inhospitable habitat for harmful bacteria and fungi. When this natural acidity is disturbed, the skin’s ability to defend itself is compromised.
The Chemistry and pH of True Soap
True soap is created through saponification, a chemical reaction combining natural fats or oils with a strong alkali, such as lye (sodium hydroxide). This process transforms triglycerides into fatty acid salts (the actual soap) and glycerol, a moisturizing byproduct. This reaction dictates the resulting pH of the final product.
Because a strong alkali is required for saponification, the finished soap is inherently alkaline. Traditional true soap typically has a high pH, often falling in the range of 9 to 10. It is impossible to produce a true soap bar with a neutral or acidic pH, as adding acid to lower the pH would stop the saponification reaction.
The high alkalinity of true soap gives it its characteristic cleaning power, as the elevated pH helps saponify fats and oils on the skin surface. This alkalinity is significantly higher than the skin’s natural pH of 4.5 to 5.5. The process of curing, where the soap bar dries and hardens over several weeks, completes the saponification and results in a milder product. However, the final pH remains alkaline.
Synthetic Cleansers and Neutral pH
In contrast to true soap, many modern cleansing products, often marketed as “beauty bars” or “body washes,” are not chemically soap. These products are synthetic detergents, or syndets, formulated using synthetic surfactants. Syndets are manufactured differently and are not bound by the chemical constraints of saponification.
The use of synthetic surfactants allows formulators to control the final pH of the product more precisely. Many syndet bars and liquid cleansers are specifically formulated to have a pH that is neutral or slightly acidic, often around pH 5.5. This pH is much closer to the skin’s natural acid mantle, making these products generally milder and less disruptive.
This difference in formulation means a product can be an effective cleanser without requiring a high alkaline pH. The majority of liquid synthetic detergents are able to be formulated in the acidic range. This allows the cleanser to remove impurities while working in harmony with the skin’s existing chemical environment.
Impact of Cleansing pH on Skin Barrier Health
When an alkaline cleanser, such as true soap, is applied, it temporarily raises the skin’s surface pH above its natural acidic level. This immediate shift disrupts the delicate balance of the acid mantle and the skin’s resident microbiome. The elevated alkalinity interferes with the activity of enzymes in the outer skin layer responsible for maintaining the skin barrier’s structure.
The temporary disruption caused by an alkaline product can lead to increased transepidermal water loss, resulting in temporary dryness. The skin possesses a natural buffering capacity and works to restore its acidic pH balance, a process that can take several hours. Repeated use of high-pH cleansers chronically challenges the skin’s barrier, potentially leading to increased sensitivity, roughness, and susceptibility to environmental irritants.
Conversely, using cleansers with a pH closer to the skin’s natural range, like many syndets, minimizes acid mantle disruption. These pH-balanced products are less likely to strip away essential lipids or significantly alter the acidic environment necessary for optimal enzyme function. By preserving the skin’s natural acidity, these cleansers support a healthy barrier, reducing the risk of dryness and irritation.