Chlorine is a chemical disinfectant used widely in public and private swimming pools to prevent the spread of waterborne illnesses. The chemical acts as a powerful sanitizer, killing bacteria, viruses, and other pathogens like E. coli and Cryptosporidium that can cause diarrhea, skin infections, or swimmer’s ear. Without this disinfection, pool water would quickly become a breeding ground for harmful microorganisms, making swimming a health risk. The concern about chlorine’s safety, however, arises not from its primary role as a germ-killer, but from the compounds it creates when it interacts with organic matter that swimmers introduce into the water.
The Chemistry Behind the Pool Smell
The strong, pungent odor often associated with a swimming pool is commonly mistaken for pure chlorine, but it is actually the smell of chemical byproducts called chloramines. These chloramines, which are a type of Disinfection Byproduct (DBP), form when the free available chlorine (FAC) reacts with nitrogen-containing organic contaminants like sweat, urine, body oils, cosmetics, and skin cells. The reaction involves chlorine combining with ammonia to form a series of chloramines, including volatile trichloramine, which is responsible for the distinct, irritating pool smell. A strong odor indicates poor water quality and a high concentration of these irritating compounds. This can sometimes signal that there is not enough free chlorine left to effectively break down the organic matter and the resulting chloramines.
Short-Term Effects on Skin and Eyes
The same chloramines that cause the strong odor are also responsible for the immediate physical discomfort swimmers often experience, particularly the irritation of mucous membranes. Swimmers frequently report eye redness, burning, and irritation, a temporary condition sometimes described as “swimmer’s eye.” This occurs because the chemicals wash away the thin, natural layer of tears coating the eyes, leaving the eyes vulnerable to irritation. Chlorinated water also strips the skin and hair of their natural oils, a protective barrier that keeps them moisturized. This process leads to dry, itchy skin and can exacerbate conditions like eczema or irritant dermatitis; for light-colored hair, the oxidation of copper in the water can sometimes cause a temporary greenish tint.
Respiratory Concerns and Inhalation Risks
The most significant health concerns relate to the inhalation of the volatile chloramines, specifically trichloramine, which readily transitions from the water into the air above the pool surface. Inhaling this gas can irritate the upper respiratory tract, leading to symptoms like hoarseness, sinusitis, and coughing. The risk is particularly elevated in indoor swimming facilities because the volatile gases are trapped and concentrated in the enclosed space when ventilation is poor. Exposure to trichloramine has been linked to the exacerbation of pre-existing respiratory conditions, such as asthma. Frequent, long-term exposure, particularly in occupational settings like pool workers, is associated with an increased risk of developing respiratory problems, though ventilation allows the irritating trichloramine gas to dissipate quickly in outdoor settings.
Steps for Safer Swimming
The most effective way to minimize the health impacts of pool chemicals is to reduce the formation and concentration of chloramines. Swimmers play a direct role by showering thoroughly with soap and water before entering the pool. This simple action removes most of the organic matter like sweat, oils, and cosmetics, which are the precursors for chloramine formation. After swimming, immediately showering again with a mild soap is necessary to wash off any residual chloramines and free chlorine, and applying a moisturizer helps replenish the natural oils. Pool facilities must maintain appropriate water chemistry, including a balanced pH level and sufficient free chlorine, and operators can reduce chloramines by using a “shock treatment.”