The familiar sting and redness that follow a swim often get blamed on “too much chlorine” in the pool. This universal experience of eye irritation, characterized by burning, tearing, and dryness, signals that the water chemistry is out of balance. While chlorine is responsible for sanitizing the water, the discomfort is not caused by the free chlorine itself. The true source of the problem is a chemical byproduct that forms when chlorine does its job of cleaning the pool.
The Chemical Misconception: Chlorine vs. Chloramines
Elemental chlorine, in the form of hypochlorous acid, is the active sanitizer that keeps pool water safe by killing germs and bacteria. A healthy pool with adequate free chlorine levels should have no strong chemical odor and cause minimal irritation. The burning sensation and the pungent, chemical smell often associated with pools are actually signs that the chlorine is reacting with contaminants. This reaction creates a group of compounds called chloramines, which are the primary irritants. Ironically, a strong “chlorine smell” indicates a pool with poor water quality, where the free chlorine has been consumed to form these irritating byproducts.
The Formation of Chloramines
Chloramines are formed through a chemical process involving the active disinfectant, free chlorine, and nitrogen-containing organic materials introduced by swimmers. These organic contaminants include sweat, urine, body oils, cosmetics, and skin cells. When the free chlorine bonds with the ammonia or nitrogen compounds found in these substances, the result is the formation of combined chlorine, or chloramines. This chemical reaction is continuous as long as contaminants are present and the pool contains free chlorine. As the chloramines accumulate, they begin to outgas from the water’s surface, particularly in indoor pools with limited ventilation, creating a layer of irritant gas that can affect the eyes, skin, and respiratory system.
The Physiological Response
The biological mechanism behind the burning sensation begins with the eye’s protective layer, the tear film. The tear film is a delicate, three-layered structure that lubricates the eye and maintains a specific, slightly alkaline pH, typically around 7.4 to 7.5. Chloramines are volatile compounds that act as corrosive chemical irritants upon contact with this sensitive surface. Exposure to chloramines strips away the tear film, dissolving its protective lipid and aqueous layers. This compromise leaves the underlying conjunctiva, the clear membrane covering the white of the eye, exposed to the pool water, leading to inflammation known as chemical conjunctivitis, or “swimmer’s eye.”
The Impact of Pool pH
While chloramines are the direct chemical irritant, the pool’s overall water chemistry, specifically its pH level, determines the severity of the eye discomfort. The ideal pH range for pool water is between 7.2 and 7.8, closely matching the natural pH of human tears. When the pool’s pH is too far outside this narrow range, it creates an osmotic imbalance against the eye’s surface. A pool that is too acidic (low pH) or too alkaline (high pH) will further disrupt the remaining tear film, exacerbating the irritation already caused by chloramines. Maintaining a balanced pH ensures the water is more harmonious with the human body, thereby minimizing the stinging and burning sensation.