Why You Shouldn't Open Your Eyes Underwater

"Keep in mind that people in pools rub their eyes more and that can cause corneal abrasions, which can lead to infections,” Layman adds.

It's just like anything else you should probably avoid: The more you expose yourself to it — in this case, waterborne chemicals and contaminants — the worse you feel.

Here's what you should watch out for the next time you go swimming:

Chlorine- and bromine-treated pools

Unfortunately, the very stuff that is added to our pools, spas and hot tubs to keep us safe can damage our eyes. Though they kill many bacteria, viruses, and parasites, chlorine and its colleague, bromine, can hurt the eye, especially after long periods of exposure and when they are mixed with the sweat and bacteria that washes off swimmers’ bodies. This creates an irritant known as chloramine, which can cause bloodshot eyes.

"Some older adults may have more sensitivity to chemicals, especially if they have dry eye disease,” Layman says. And people of all ages are more likely to have dry eyes these days, because when we look at a screen — computer, TV, phone — we blink less. A humidifier can help combat this. You can also limit your screen time or try the 20/20/20 strategy: Every 20 minutes, look away from the screen for 20 seconds to see something 20 feet away, the experts at Mayo Clinic recommend.

Chlorine, “a chemical irritant,” can cause red eyes, blurred vision, light sensitivity and “feelings of grittiness and dry eye,” Layman says. It can also “disrupt the tear film,” which is the protective, three-layer coating that keeps your eye moist and helps you cry.

This damage inflicted by chlorine is typically temporary. The same is true for bromine, which can also cause redness and teary eyes, especially when a pool's chemical and pH levels aren't properly calibrated.

And remember: Disinfectants like chlorine and bromine don't kill all contaminants. They can't fully protect you from the viruses, bacteria and parasites that can make you sick.

A pool is “a shared water experience,” as the Centers for Disease Control and Prevention (CDC) puts it, but many people don't think of it that way. That's why some people go in the water when they shouldn't: that is, when they're sick (with diarrhea) or have open wounds. Various foreign objects can fall into a pool and muddy the water: insects, leaves, diapers, etc. ‘Pink eye’ (conjunctivitis) and adenoviruses can be caught even in properly disinfected pools.

Saltwater pools

Saltwater can also irritate the eye, but the effects typically aren't as severe as what you might experience in a chlorine- or bromine-treated swimming pool, spa or hot tub.

"In most cases, a saltwater pool won't have the same harsh effects of a traditional chlorine pool,” Layman says. (The ocean is similar, though as with all bodies of water, other contaminants may be present.)

If your eye feels irritated after swimming in saltwater, you should flush it out and rinse it with either cool water or a sterile saline (mild salt) solution as soon as possible and for at least 15 minutes, over the sink or in the shower, Layman recommends.

3. Opening eyes underwater can throw off balance and orientation

Beyond infections, opening your eyes underwater can be disorienting, especially when you're swimming.

"We're not accustomed to moving while lying down, as it were,” says Jennifer M. Groh, a professor of psychology, neuroscience and neurobiology at the Duke University School of Medicine, whose work focuses on how vision and hearing interact. And swimming can be a uniquely unbalancing experience, she adds.

"You've been swimming along with your eyes closed, but then you opened them ... and it shifts the orientation of the sensors that we use for knowing that we're moving,” Groh explains. “That can be an aspect of why it can feel a little disorienting.” What's more, if you get cold water in your ear, “especially if you get it in only one side,” that can make you dizzy, she adds.

Think about how your head is oriented underwater, Groh says. “How do we know we're moving through space? It's partly the effort that we're taking to move, and it's partly your vestibular system, your sense of balance, which is measuring how fast your head is actually moving.”

Opening your eyes and straining to see can change that measurement, a bit: It can alter how you feel you're moving when you're swimming. That can be a tricky transition.

Goggles, of course, can change all that. They can help you keep your eyes open the whole time.