Swimming in a pool can sometimes lead to illness, often grouped under the term Recreational Water Illnesses (RWIs). These illnesses result from a complex interaction between water disinfectants, contaminants introduced by swimmers, and the resilience of certain germs. Understanding the two primary causes—microbial infection and chemical irritation—can help swimmers take appropriate preventative measures.
Understanding Waterborne Pathogens
The most common cause of infectious illness from pool water is the presence of microorganisms like parasites, bacteria, and viruses. These pathogens are usually introduced when an infected person swims, often through microscopic amounts of fecal matter. Swimmers become infected when they accidentally swallow the contaminated water, allowing the germs to enter the gastrointestinal tract.
The parasite Cryptosporidium (Crypto) is a resilient concern and the leading cause of waterborne disease outbreaks in pools. Protected by a tough outer shell, Crypto is highly resistant to chlorine disinfection. While chlorine kills most bacteria and viruses quickly, Crypto can survive in properly treated pool water for over seven days. An infected swimmer can shed millions of these parasite oocysts into the water. If others ingest even a small amount, they risk developing cryptosporidiosis, which causes prolonged watery diarrhea. Other pathogens transmitted this way include Giardia and norovirus, which also cause gastrointestinal distress.
Illnesses Caused by Chemical Irritation
Not all swimming-related discomfort is caused by infectious pathogens; a significant portion results from chemical reactions within the water. When disinfectants like chlorine or bromine mix with organic substances introduced by swimmers—including sweat, urine, dirt, and cosmetics—they create Disinfection Byproducts (DBPs).
The most notable byproducts are chloramines, which cause the strong, pungent “pool smell” often mistakenly attributed to high chlorine levels. This smell signals that the chlorine is reacting with swimmer waste and becoming less effective at killing germs. Chloramines are volatile compounds, particularly trichloramine, that off-gas from the water’s surface into the air.
Inhaling these gas-borne chloramines causes non-infectious symptoms like red, stinging eyes and irritation of the nasal passages and throat. Gaseous chloramines can also irritate the respiratory system, potentially leading to coughing or exacerbating asthma symptoms in sensitive individuals.
Common Conditions and Symptoms
Pool exposure can result in several recognizable ailments linked to either microbial or chemical causes. Gastrointestinal issues, such as diarrhea, nausea, and vomiting, are the most frequent infectious illnesses. They typically arise from swallowing water contaminated with parasites like Cryptosporidium or bacteria. Symptoms usually appear days after exposure and can last for one to three weeks.
Skin rashes are another common outcome, including folliculitis, often called “hot tub rash.” This condition is caused by the bacterium Pseudomonas aeruginosa, which thrives in warm water. It causes itchy, red bumps on the skin, typically developing a few days after contact with contaminated water.
Swimmer’s ear, or otitis externa, is a bacterial infection of the outer ear canal. It occurs when water remains trapped inside the ear after swimming, creating a warm, moist environment where bacteria, often Pseudomonas, multiply and cause pain, itching, and discharge. Respiratory symptoms, such as coughing, chest tightness, or eye redness, are frequently linked to chloramine exposure and chemical irritation, rather than a true respiratory infection.
Essential Steps for Safe Swimming
Preventing pool-related illness requires personal hygiene and awareness of water quality. Showering thoroughly with soap before entering the pool is highly effective, as this action removes body waste, dirt, and sweat. This significantly reduces the organic material available to react with chlorine and form irritating chloramines.
Swimmers should avoid entering the water if they have diarrhea. Those diagnosed with Cryptosporidium must wait two weeks after symptoms stop before swimming again, as the parasite can continue to be shed even after diarrhea resolves. Swimmers should also make an effort to avoid swallowing pool water, as ingestion is the primary route of infection.
To prevent swimmer’s ear, dry the ears thoroughly after leaving the water, using a towel or tilting the head to drain trapped moisture. Public pool users can also check the posted water chemistry, looking for a free chlorine level between 1 and 3 ppm and a pH between 7.2 and 7.8, which indicates effective disinfection.