Red-eyes the true indicator that someone has peed in the pool

Chlorine was first used in American sanitation back in 1918, starting with drinking water. Chlorinated water, however, makes most people think of a trip to the swimming pool, where it’s used to kill microbes that are likely being introduced from your fellow swimmers. A trade-off in this arrangement is that opening your eyes under the water often proves quite irritating, leaving your eyes red and itchy. That redness, however, only occurs once a second ingredient is added to the water: pee.

Once the chlorine mixes with pee in water, it can react with the urea and uric acid to create CNCl and NCl₃, two poisonous gasses that can pose a health risk to lungs, hearts and nerves. They’re also the source of the “chlorine” smell associated with pools. Aside from all of these side effects, chlorine isn’t even a perfect solution to sanitizing a pool, as it can leave some bacteria alive for days.

So is this a lost cause? Are we doomed to pee-induced irritation and poisoning while fighting contamination from our own sweat and (occasionally) feces? It’s unlikely that we’ll be able to convince swimmers of all ages to stop peeing in the chlorine, but fortunately that’s not the only way to kill microbes in a pool. A number of different treatments are available, but if your pool doesn’t use them, at least remember to bring your goggles.

Source: Your swimming pool red-eye isn’t from chlorine—it’s from urine by Gwynn Guilford, Quartz