CDC: Red eyes while swimming caused by urine, not chlorine There's a reason why most pools have showers on site UPDATED 5:21 PM EDT Jun 19, 2015 Sean Gallup/Getty Images Photos Sean Gallup/Getty Images Those red eyes you get from swimming aren't caused by chlorine, according to an official with the Centers for Disease Control and Prevention. And the substances in the pool that do cause your bloodshot eyes will probably make you a little seasick. “Chlorine binds with all the things it’s trying to kill from your bodies, and it forms these chemical irritants. That’s what’s stinging your eyes. It’s the chlorine binding to the urine and sweat,” says the appropriately named Dr. Michael J. Beach, associate director of the CDC's Healthy Water program. Furthermore, reports Complex.com, the fabled dye that causes the water in the pool to change colors if somebody relieves their bladder in the water? It doesn't really exist. "It's a myth. It's about scaring people into not urinating in the pool," Beach says. In other words, there's an extremely valid reason why most swimming pools also offer showering facilities. .