The burning sensation and redness you sometimes feel after a swim in a chlorinated pool are a common, yet frequently misunderstood, side effect of water chemistry. Many swimmers assume this discomfort signals an over-chlorinated pool, but the reality is more complex than a simple excess of disinfectant. The irritation is not typically caused by the chlorine added to keep the water clean, but rather by the chemical byproducts that form when that chlorine is doing its job. Understanding this reaction is the first step toward enjoying a more comfortable and eye-friendly swimming experience.
It Is Not Just Chlorine
The free chlorine added to the pool water is an effective disinfectant designed to eliminate bacteria and other pathogens. However, when this active chlorine encounters nitrogen-containing compounds, it initiates a chemical process that produces a different class of irritants called chloramines, also known as combined chlorine. These compounds, not the free chlorine itself, are the primary cause of the stinging eyes, dry skin, and the strong “pool smell” often associated with swimming.
The active form of chlorine, hypochlorous acid, reacts with ammonia and other nitrogenous substances to form compounds like monochloramine, dichloramine, and trichloramine. These chloramines are significantly less effective at sanitizing the water than free chlorine and are highly volatile, easily turning into a gas that irritates the sensitive mucous membranes of the eyes. Ironically, a strong chemical smell in a pool indicates a high concentration of these irritating chloramines, suggesting a problem with water quality, not a well-maintained pool. When chloramine levels climb too high, they strip away the tear film—the thin, protective layer of moisture on the surface of your eyes—leading to redness and a gritty, uncomfortable feeling.
Where the Irritants Come From
The nitrogen and organic material that fuel the formation of chloramines are introduced into the pool by the swimmers themselves. Human sweat and urine are major sources of ammonia and urea, which readily combine with the chlorine in the water. Other contaminants include dead skin cells, saliva, and various personal care products washed off the body, such as lotions, cosmetics, and hair products.
When a pool has a high bather load, the influx of these contaminants accelerates the chemical reaction, leading to a rapid buildup of chloramines. This production of irritants is compounded by imbalances in the pool’s acidity level. The ideal pH for pool water is a narrow range, typically between 7.2 and 7.8, which closely matches the natural pH of human tears.
If the water’s pH drifts too high or too low outside this comfortable range, the water itself becomes an irritant, exacerbating any discomfort caused by chloramines. An improper pH level can also affect the efficiency of the free chlorine, leaving more contaminants in the water to react and create stinging byproducts. Therefore, the perfect chemical environment for eye irritation is a combination of high chloramine content and a poorly balanced pH.
Steps for Immediate Relief
The most effective action to prevent eye irritation is to reduce the amount of organic material entering the water. Taking a quick shower with soap before entering the pool can remove the majority of sweat, oils, and personal care products from your skin. This simple step minimizes the available nitrogenous compounds that can react with the chlorine to form chloramines.
Relief and Prevention Measures
- Wearing a pair of snug-fitting swim goggles creates a physical barrier, preventing the pool water and its chemical byproducts from contacting the eyes entirely.
- If your eyes begin to burn during or after swimming, rinse them immediately with fresh, clean tap water for several minutes.
- A more soothing and effective option is to use a sterile saline solution or artificial tears to flush the irritants and help restore the protective tear film.
- Avoid using over-the-counter eye drops advertised to “get the red out,” as these products can cause a rebound effect, potentially worsening the redness and dryness over time.
For persistent irritation, check the pool’s maintenance log or ask the operator about the water chemistry. Ensure that the free chlorine level is correct and the pH is balanced within the optimal 7.2 to 7.8 range. Addressing the root cause—the chloramines and pH—is the best way to ensure clear and comfortable vision after your swim.