Chlorine is the standard chemical used globally to disinfect swimming pool water, serving a fundamental public health purpose. This chemical ensures the water is safe by rapidly destroying harmful microorganisms, such as E. coli, Salmonella, and viruses, which can cause illnesses like diarrhea and swimmer’s ear. Without this sanitizing agent, pools would quickly become breeding grounds for pathogens, posing a significant risk to all users. The common irritations and distinct “pool smell” are not typically caused by the free chlorine that kills germs, but rather by chemical compounds that form when chlorine interacts with substances introduced by swimmers.
Understanding Disinfection Byproducts
The health effects commonly attributed to chlorine are actually caused by a group of chemicals known as Disinfection Byproducts (DBPs). DBPs are created through a chemical reaction between the chlorine disinfectant and organic materials introduced by swimmers, such as sweat, urine, dead skin cells, cosmetics, and personal care products.
The reaction between chlorine and nitrogen-containing organic matter, like urea from urine and sweat, forms chloramines (monochloramine, dichloramine, and trichloramine), collectively known as combined chlorine. The strong, characteristic “pool smell” that many people associate with a clean, heavily chlorinated pool is actually the volatile gas trichloramine (NCl3). This pungent odor signals a high concentration of chloramines and a high organic load in the water.
Trichloramine is highly volatile and easily escapes the water, accumulating in the air above the pool surface. In indoor facilities, this respiratory irritant can accumulate in the breathing zone of swimmers and staff if the ventilation system is inadequate. The concentration of trichloramine is directly linked to the amount of organic material present in the water. Beyond chloramines, the chlorination process also creates other DBPs, including trihalomethanes (THMs) and haloacetic acids (HAAs).
Physiological Effects of Exposure
Exposure to volatile DBPs, particularly trichloramine, causes symptoms ranging from mild irritation to serious respiratory issues. The most immediate and common effect is irritation of the eyes and skin. Chloramines react with the thin layer of tears protecting the eyes, causing redness, stinging, and burning.
Contact with combined chlorine compounds can also lead to skin irritation, presenting as dryness, itchiness, or a rash. Prolonged exposure compromises the skin’s natural protective barrier by stripping away moisturizing oils. This disruption can trigger or worsen pre-existing conditions like eczema in sensitive individuals.
The most significant health concern relates to the respiratory system, as trichloramine gas is easily inhaled. Exposure to this gas irritates the mucosal lining of the airways, leading to acute symptoms such as coughing, wheezing, and nasal irritation. Chronic exposure, particularly observed in competitive swimmers and pool workers, has been associated with an increased risk of developing asthma and other allergic respiratory diseases. In extreme cases, long-term exposure to high concentrations of airborne chloramines has been linked to a condition resembling occupational asthma, sometimes referred to as “lifeguard lung.” Young children and individuals with pre-existing respiratory conditions are considered more sensitive.
Practical Steps for Safer Swimming
Swimmers can take several simple steps to significantly reduce their exposure to irritating disinfection byproducts. The single most effective action is showering thoroughly with soap and water before entering the pool. This pre-swim rinse removes organic matter—sweat, oils, and cosmetics—which are the primary reactants that form chloramines.
Swimmers should also shower immediately after leaving the pool to rinse off residual chemicals and minimize DBP contact with the skin. Applying a fragrance-free moisturizing cream or lotion helps to restore the skin’s moisture barrier. Drinking plenty of water during a swim session also helps to maintain the body’s internal balance and mitigate drying effects.
Facility management is crucial for maintaining a healthy environment, especially in indoor pools where ventilation is necessary. Proper air handling systems are necessary to exhaust the heavier trichloramine gas that settles above the water surface. Well-managed pools keep the level of combined chlorine in the water low, often limited to 0.4 parts per million or less, ensuring a healthier atmosphere.