That sharp chlorine smell at the swimming pool is not chlorine, and the CDC says it means the opposite of what you assume; a properly maintained pool should barely smell of anything at all

Every American summer, the same scene probably plays out at community pools, gym lap lanes, and hotel rooftop pools from Miami to Seattle: someone walks in, breathes in that sharp, stinging smell, and says, “Wow, they really dumped the chlorine today.” According to the Centers for Disease Control and Prevention, that assumption is wrong. That smell usually means water needs more chlorine, not less. Here's what's actually going on in the water you're about to jump into.

The smell you know is not the chemical you think
Pure chlorine, the chemical that really kills germs, has barely any smell. Chloramines are chemical byproducts formed when chlorine reacts with things swimmers bring into the water, and they’re the reason your eyes and throat sting. The CDC says chlorine reacts with substances like sweat, dirt, skin cells, deodorant, makeup, and urine to form these irritants, which reduce the amount of active chlorine available to disinfect the water. So a pool that smells strongly of "chlorine" is really telling you that it is carrying a heavy load of body byproducts and is running low on the clean chlorine it needs to do its job.

Why indoor pools hit you harder
There’s a reason your eyes may start watering within seconds when you walk into an indoor natatorium. Chloramines don’t just stay in the water; they off-gas into the air immediately above the surface. According to the CDC's guidance for pool operators, this gas tends to build up most quickly indoors, and the problem can be worse in winter, when facilities pull in less air from outside to save on heating costs. Open air and breeze give outdoor pools a natural assist, which is a big part of why that overwhelming “pool smell” shows up far more at an indoor gym lap pool than at a backyard party.

It's not just your eyes
The irritation goes beyond stinging eyes, and there's real research behind it. A study of 624 pool workers at 38 Dutch swimming facilities published in the European Respiratory Journal titled ‘Exposure to trichloramine and respiratory symptoms in indoor swimming pool workers’ found that workers exposed to higher levels of trichloramine reported more upper respiratory symptoms than those with lower exposure. According to the CDC, anyone in the pool area, including non-swimmers, can experience nasal irritation, coughing, wheezing, and asthma attacks in individuals who already have asthma. Additionally, they may suffer from red, itchy eyes and skin irritation.

This is not hypothetical. According to a CDC outbreak investigation published in the Morbidity and Mortality Weekly Report, 24 people, including a 6-year-old boy who was hospitalized, became ill after swimming in an indoor motel pool in Nebraska in December 2006. Investigators linked the outbreak to high levels of toxic chloramine that built up in the air above the pool due to poor ventilation.

Why this matters more than you'd think in the US
Here’s the part that may change the way you look at the neighborhood pool. A five-state CDC surveillance report examined 84,187 routine inspections of public pools, hot tubs, and water playgrounds in 2013 and found that about 12.3 percent of inspections with recorded outcomes, or nearly 1 in 8, resulted in immediate closure due to serious health and safety violations, including inadequate disinfectant levels. A strong chemical smell isn’t just unpleasant; it can also be an early sign that a facility is falling behind on maintenance.

How to actually protect yourself this summer
The good news is that you don’t need a degree in chemistry to swim smart. The CDC's prevention guidance points out that a few simple habits can make a real difference:

Before getting in, take a proper shower. Even a quick one-minute rinse will wash away most of the sweat, lotion, and grime that react with chlorine. Never use the pool as a bathroom. Pee is a major source of chloramine, and it’s totally preventable. Kids should wear a bathing cap and take bathroom breaks every hour or so instead of waiting for an obvious accident. If a pool smells overwhelmingly of “chlorine,” don’t assume it’s cleaner. Inform the lifeguard or the front desk, as a strong smell can be an indication that the water requires fresh disinfectant. For indoor pools, keep an eye on the air. If it feels stuffy or your eyes start to burn within minutes, poor ventilation is likely part of the problem.

The bottom line
The next time you catch that familiar ‘pool smell’ in a hotel lobby or community center, remember it's less a sign of cleanliness and more a signal worth paying attention to. A properly run pool shouldn’t smell strongly of chemicals at all. If it smells strong, the water is telling you something, and it pays to listen.