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The Highs and Lows of pH

By: Kirsten Sheridan
Posted: June 9, 2008

The defenses are up, the barrier is intact and the level of protection is high. Yes, the skin is being referred to—healthy skin, that is. There are many contributors to the formation of healthy skin, but of great importance is its pH level.The human body’s entire system depends upon maintaining a pH balance, which promotes its general health and well-being. In relation to the skin, however, changes in pH can have significantly dramatic effects. Healthy pH provides the stratum corneum with a slightly acidic environment. Poor product choices, harsh exfoliants and physical trauma all greatly affect this acidic microniche that offers protection from an offensive world.

Concept of pH

pH is an acronym for the power, or potential, of hydrogen. Simply put, the power of hydrogen indicates the acidity or alkalinity of a solution. This is measured in units called logarithms, using a scale known as the pH scale. This runs from pH 0–pH 14. A solution that is highly acidic will have a lower pH number. So, for example, battery acid, which is highly acidic, measures around pH 1. Acidic solutions contain primarily hydrogen ions (H+), so a pH 1 solution would be composed mostly of hydrogen ions. At the opposite end of the scale, solutions mainly are made up of hydroxyl ions (OH-). So, for example, lye, which is in the range of pH 13–14, is highly alkaline. pH neutral denotes the middle of the scale and is represented by pH 7. A neutral pH solution contains an equal number of hydrogen and hydroxyl ions, and is neither acidic nor alkaline. Distilled water is a good example of a pH-neutral solution.

When measuring pH, the unit of logarithms expresses a tenfold change from the previous concentration, similar to the Richter scale that is used to measure earthquake activity. For instance, a solution measuring pH 3 indicates 10 times fewer hydrogen ions than a pH 2 and is, therefore, 10 times less acidic in nature. Think of hydroxyl acid preparations used for peeling and exfoliation. A hydroxyl acid preparation of pH 2 versus pH 3 will provide very different results.

The acid mantle

One of a human’s first lines of defense is the acidic environment created in the upper layers of the epidermis, courtesy of the acid mantle, which is a protective outer coating. The body’s acid mantle is a key mechanism that keeps out unwanted visitors, particularly of the bacterial variety. The environment is full of harmful and not-so-harmful bacteria that are just waiting for an open invitation to cause havoc on the skin. The acid mantle’s slightly acidic pH of 4.5–5.5 wards off harmful bacteria, restricting or preventing its growth on the skin. Fortunately, the bacterial flora that is nonpathogenic—or beneficial to the skin—thrives in the acidic environment created by the acid mantle. If it is compromised and a more neutral pH develops, bacteria such as staphylococcus and fungi such as candida may proliferate.

The acid mantle is formed from free fatty acid secretions from the sebaceous glands, lactic acid from the body’s eccrine sweat glands and microbial metabolites that rendezvous in the stratum corneum. Enzymes and specialized proteins also are involved in the formation of this essential acidic environment. This carefully orchestrated meeting provides the healthy pH balance needed to protect and defend the skin, which is so essential to barrier function. Due to changes in the skin as people age, its pH may become slightly elevated.