Chlorine, widely used in pools and municipal water systems for sanitation, is inherently pH-active. Its chemical form and effectiveness are directly tied to the acidity or alkalinity of the water it treats. When this treated water contacts the body, particularly the skin, it initiates a chemical interaction that temporarily shifts the body’s protective surface balance. This influence stems from chlorine’s oxidizing nature and the specific pH of the water carrying it.
Understanding pH and Chlorine Chemistry
The pH scale is a logarithmic measure of the concentration of hydrogen ions in a solution. In water treatment, chlorine is typically added in forms like sodium hypochlorite or chlorine gas, both of which react with water to form two primary disinfecting agents: hypochlorous acid (\(\text{HOCl}\)) and the hypochlorite ion (\(\text{OCl}^-\)). These agents exist in a dynamic equilibrium controlled by the water’s pH.
Hypochlorous acid is the more potent sanitizer. The water’s pH determines the ratio between these two forms; at a lower, more acidic pH (below 7.5), hypochlorous acid predominates, maximizing the chlorine’s germicidal power. Conversely, as the water’s pH rises toward the alkaline side (above 7.8), the equilibrium shifts, and a larger percentage of the chlorine converts into the less effective hypochlorite ion.
Maintaining the proper pH of the water is a balance between sanitation effectiveness and swimmer comfort, with pool water often targeted for a slightly alkaline range of 7.2 to 7.8. While the addition of chlorine compounds can initially shift the water’s pH, the water’s natural buffering capacity usually prevents extreme changes. Ultimately, the water’s pH governs the chlorine’s activity.
Chlorine’s Impact on the Skin’s Acid Mantle
When chlorinated water encounters the human body, it disrupts the skin’s surface defense layer, known as the acid mantle. This mantle is a thin, slightly acidic film composed of sweat, sebum, lactic acid, and amino acids, which typically maintains a pH between 4.5 and 5.75. This natural acidity is crucial for the skin barrier’s function, helping to lock in moisture, regulate the skin’s microflora, and protect against environmental pathogens.
The pH of treated water, even at the optimal pool range of 7.2 to 7.8, is significantly higher than the skin’s natural pH. This difference causes an immediate neutralizing effect on the acid mantle, pushing the skin toward a more alkaline state. When the skin becomes more alkaline, its ability to synthesize necessary fatty acids and maintain barrier lipids is impaired, leading to a compromised protective layer.
In addition to the pH effect, chlorine is a strong oxidizing agent that strips away the skin’s natural oils and sebum. The loss of these protective lipids leads to increased transepidermal water loss, resulting in the common post-swim sensations of tightness, dryness, and irritation. Hair is similarly affected, as the chemical exposure can damage the outer cuticle layer, making strands feel rough and brittle.
Mitigating pH Disruption from Chlorinated Water
Rinsing thoroughly with fresh, non-chlorinated water immediately after exiting the pool is the first step. This initial rinse physically removes the bulk of the residual chlorine and chloramines clinging to the skin and hair. Following the rinse, using a mild, pH-neutral, or slightly acidic cleanser is recommended to wash away any remaining chemical residue and help re-acidify the skin. Some swimmers also use a diluted solution of ascorbic acid (Vitamin C), which chemically neutralizes chlorine and can be applied to the skin before showering.
Rehydrating the skin is necessary to repair the lipid barrier. Applying a rich moisturizer or body cream immediately after showering, while the skin is still slightly damp, helps to seal in moisture. Look for products containing ingredients like ceramides, glycerin, or oils that support the skin’s natural barrier function, helping the acid mantle return to its healthy, slightly acidic state.