Chlorine is routinely added to recreational water, such as swimming pools and hot tubs, to eliminate germs and maintain hygiene. It functions as a powerful disinfectant, reacting with and neutralizing harmful pathogens like bacteria and viruses to keep the water safe. A frequent concern for swimmers is whether this chemical is absorbed into the body through the skin. Answering this requires examining the chemical forms of chlorine in the pool, the skin’s biological defenses, and alternative exposure pathways.
Dermal Uptake of Chlorine Compounds
When chlorine is added to water, it forms hypochlorous acid (HOCl) and hypochlorite (OCl\(^{-}\)), collectively known as “free chlorine.” These are the active disinfectants. Scientific understanding suggests that the direct systemic absorption of these primary chlorine compounds through intact skin is insignificant for most swimmers.
The skin’s outermost layer, the stratum corneum, acts as an effective barrier against these water-soluble, charged, and reactive molecules. Because they are lipid-rich, these molecules have limited ability to penetrate the skin deeply enough to enter the bloodstream rapidly. Studies on topical applications of hypochlorous acid for wound care indicate that systemic absorption is negligible.
The main concern for dermal uptake involves Disinfection By-Products (DBPs) created when chlorine reacts with organic matter. DBPs, such as haloacetonitriles (HANs) and chloral hydrate (CH), are often more lipid-soluble than free chlorine, allowing them to pass through the skin barrier more readily. Percutaneous absorption of these by-products is a recognized route of systemic exposure.
Absorption rates for these by-products are significantly influenced by environmental factors common in pool settings. Warmer water temperatures increase the skin’s permeability and enhance the rate of passage. The duration of exposure and the total submerged surface area also increase the potential for DBP uptake.
How Chlorine Affects the Skin Barrier
Although primary chlorine compounds are not readily absorbed, they have a direct effect on the skin’s surface. Chlorine acts as an oxidizing agent and a desiccant, impacting the skin barrier structure. This surface interaction causes common post-swim discomforts like dryness and itching.
The skin’s natural moisture barrier is composed of lipids, which prevent water loss. Hypochlorous acid disrupts this lipid matrix, stripping away natural oils and compromising the barrier’s integrity. This oxidative damage leads to increased transepidermal water loss, causing the characteristic dry, tight feeling after swimming.
Chlorine also interferes with the skin’s Natural Moisturizing Factors (NMFs), such as amino acids and urea, which help retain hydration. Stripping protective lipids and washing away NMFs makes the skin vulnerable. For individuals with sensitive skin, this barrier disruption can trigger irritation and redness.
This reaction is a localized physical and chemical response. Repeated exposure without proper post-swim care can lead to cumulative damage and persistent dryness. This surface damage may also temporarily increase skin permeability, potentially enhancing the uptake of trace organic by-products.
Inhalation of Volatile Chlorine Byproducts
A more significant health concern related to chlorinated water involves the respiratory system. This pathway centers on the inhalation of volatile compounds that off-gas from the water’s surface, especially in indoor or poorly ventilated facilities. The distinct, sometimes pungent, “chlorine smell” of a pool is not from chlorine itself, but from these airborne by-products.
These volatile compounds are chloramines, or combined chlorine, which form when free chlorine reacts with organic substances introduced by swimmers. The primary volatile agent is trichloramine, which readily transitions into a gas and concentrates above the pool water. This compound is largely responsible for the eye and respiratory irritation often associated with swimming.
Inhaled trichloramine is rapidly absorbed through the highly permeable tissues of the lungs and respiratory tract. This makes inhalation a far more efficient method of systemic exposure than dermal uptake of primary chlorine species. Exposure can irritate mucous membranes, leading to symptoms like coughing and wheezing.
For regular swimmers, chronic exposure to trichloramine has been linked to an increased risk of developing or exacerbating asthma-like symptoms. The concentration of these by-products is highest in indoor pools where poor ventilation allows them to accumulate. Airflow systems that exhaust the chloramine-polluted air are necessary to mitigate this risk.
Reducing Exposure and Post-Swim Care
Swimmers can take proactive steps to minimize skin irritation and exposure to volatile by-products. These actions focus on reducing chloramine formation and neutralizing chemical residue on the skin.
Showering thoroughly with soap before entering the water is highly effective. This removes organic matter (sweat, oils, cosmetics) that reacts with chlorine to form irritating chloramines. This action benefits all swimmers by reducing the overall concentration of volatile compounds in the pool environment.
Post-Swim Care
Immediately after exiting the pool, rinsing off with soap and water washes away residual chlorine and by-products. Following this, applying a moisturizer helps replenish the lipids and Natural Moisturizing Factors stripped away by chlorine. Some swimmers also use topical products containing Vitamin C, which neutralizes chlorine on the skin’s surface.
To limit respiratory exposure, swimming in outdoor pools is beneficial, as open air disperses volatile chloramines. If swimming indoors, seek facilities with high-functioning ventilation and air handling systems. These routines minimize the chemical burden and help maintain the skin’s natural barrier function.