Why Do Your Eyes Get Red in the Pool?

Maybe you’ve had this experience. After a long day at the pool, your eyes start stinging a little. They might even turn red, a burning, itchy bloodshot mess. Now you might think that’s the price you pay for swimming without goggles and that your eyes are just sensitive to the chlorine in the water. The real answer is a lot more disgusting. Apologies in advance. The stinging redness actually means the water you’ve
been in for the past hour includes a fair amount of urine, sweat, or even poop. Yep. Your eyes are actually doing you a sort of favor and screaming out in their bloodshot pain that
you’ve been in water that’s less than sanitary. To be fair, chlorine is still involved. The real offenders here are a class of
chemicals called chloramines which form when chlorine reacts with the
nitrogen-rich ammonia or similar compounds in those bodily fluids. Pee and sweat for example both contain urea, a molecule with two ammonia like parts. When urea comes in contact with chlorine,
it swaps out its hydrogens for chlorine, and voila, chloramine is born. That chloramine is what actually irritates your eyes, not the cleaning stuff that was put in the pool, originally. So how do you know whether you should risk jumping into the water? Go with your nose. It turns out that the chlorine odor you associate
with pools isn’t actually chlorine, that’s also chloramine. And, not only is the smell a sign that
there’s a lot of bodily fluid in the pool, but because all that chlorine is bound to nitrogen,
it means that there’s probably not that much free chlorine left to do what it’s meant to do: disinfect. That’s because chlorine only works well
ripping apart bacteria and destroying viruses when it’s dissolved in water as hypochlorous acid. Once it’s part of a chloramine molecule,
that killing power goes way down. So if there is a strong smell to the pool you might
want to reconsider your swim. And if you want to help rather than hinder the red-eye problem, take a quick shower before you swim. In about a minute, you can wash away any sweat or dirt that you might otherwise bring into the pool,
that would make more chloramines. And I shouldn’t have to say it:
but pretty please, don’t pee in the pool. And thank you for watching this episode of SciShow. We will be uploading more summer themed videos all week, so make sure to subscribe if
you want to learn more weird facts like this. And if you want to impress your friends
with science while you’re swimming, check out these awesome new SciShow Beach Towels,
available at DFTBA.com/SciShow That’s right, We’re making beach towels. Sorry to everyone in the southern hemisphere.
I know that it’s winter there. [Outro theme]


  1. More chloramine doesn't necessarily mean less chlorine (for example if you add more chlorine later on) right? Unless I'm missing something?

  2. Don't pee in the pool, it attracts sharks. Now be a good samaritan and spread this information far and wide!

  3. Why does drinking milk help you deal with spicy foods? Does it have to do with restoring pH? Or does something in the milk react with capsaicin independent of acidity?

  4. If a strong chlorine smell means more pee, then somebody must have been secretly peeing into my bottle of bleach I use to clean the floor with.

  5. The Urea is from sweat. This is why swimming is so good for losing weight. Who pees in the pool,seriously ? I don't believe people just pee in pools like that. Maybe, its a strictly US thing that people are to fat and lazy and just go whenever they want? I personally never seen anyone just using swimming pool as a toilet in my country.

  6. Could you guys make a video about LED eyes causing blindness? Is it a myth or is there some truth to it? I've seen mixed results on the internet.

  7. Do you ever look at the title of a video, answer the question it poses in your head, and then not watch it? I just took one look at this, went "Chlorine obviously…" then clicked to comment lol

  8. At a pool party my dad dumped way too much chlorine in the pool believe me that chlorine will make your eyes red on its own dump some in your eyes one day and see what happens

  9. This video would do better to cover the physiological effects of why your eyes turn red to pretty much anything not just chlorine

  10. How about the shower ? every time I come out the shower at my house my eyes get worst than a pool.

  11. so what you're saying is….if I were to pour hypochloric acid in my eyes they wouldn't get irritated?….. challenge accepted

  12. but when i swim in non chlorinated water my eyes don't get red, maybe its a coincidence
    Never mind im dumb chlorine plays a big part

  13. As a former Lifeguard, that is incredibly disgusting, and I'm now glad that I don't swim in pools very often anymore.

  14. you really should have made the beach towels reactive to the sun so they showed when to apply more sunscreen. (not sure that is possible, but would be awesome)

  15. 2:00 reminds me of the joke:

    Two moms are talking to each other.
    Mom A: "And I was so embarrassed because he got kicked from the poll because he peed in it."
    Mom B: "But everyone does that."
    Mom A: "Not from the 10m board."

  16. Oh good lord, I used to take swimming lessons at a somewhat decrepit local middle/highschool pool. I always thought it was one of the more regulated pools, as the smell of chlorine (ahem) was overpowering… one time, my eyes caused me to cower in pain for the rest of the day, pressing my head into various pillows, blankets, and the like. Those other little suckers were actually just letting loose constantly.

  17. So pretty much every pool I'm in… my eyes hurt… So basically I drink pee and poop and sweat put in a big blender and blended together


  19. Fml. I can’t even swim in a pool for more than 20 minutes because if I do, my eyes will be unbearably painful for the next 3 hours and the reason is that people are peeing in the pool? Please, public urination is a crime. Don’t pee in the pool, it’s just disgusting

  20. …are you sure—public pools here switched, ca 1990, to 'bleach' (hypochlorite) and carbon dioxide but, the stinging was so bad it fogged the eyes and I had to stop swimming a mile daily (1600 m lapper's mile, cf a land mile ca 1609.34 m, and a nautical mile 1852.00 m)…

  21. Who else punked out when he said it's a lot more disgusting and apologized in advance? 🙋🏾‍♀️

  22. Awesome! Poop Eye! Guess what is also fun? When that redness doesnt go away because that poop contained ecoli or maybe even the Adeno virus. Think a few hours of red eye is fun, get some "PINK EYE" from a poorly taken care of pool and it will be weeks of pain and loos school/work! If you are lucky, some peeps with pink eye get really awesome morbidity!!! Milky white film on the eye, bleeding…..a few lucky participants get to experience a cornea peel (Ophthalmologists will love you, big money maker for them!)! Seriously, there is literally no public pool anywhere that is not a petri dish of infection. Would you lick the person in the pool next to you that you dont know? Take a close look at them. Would you put your eye ball right on that persons butthole? Well, you do when you get in that pool water.

  23. that’s great but I go to a community pool so how am i supposed to tell everyone to stop peeing? 😔

  24. Today I have gone swimming with my friends and we were first to go there My eye is not red but my face I mean cheeks are so red I wanna know why ❓

  25. It has happened me from getting sea water splashed in my eyes from traveling on a speedboat out at sea. This is why I am looking at these videos. My eyes are completely blood shot red and seriously sore

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