Why Does Salt Water Hurt My Eyes?

Why does salt water hurt your eyes? Why doesn’t salt water sting a whales’ eyes? Is it harmful to open your eyes in a swimming pool?

Dr. Michael Steinmetz answers of all these burning questions related to salt water and pool chlorination in the video below.

Ask a Scientist: Underwater Eyes

With Dr. Michael Steinmetz

Question:

If our tears are salty, why does salt water sting our eyes?

Answer:

Our tears contain a variety of salts, but the ocean water is far saltier, and we know from science that water tends to move from an area of low salt concentration, to an area of high salt concentration. So when we open our eyes in the ocean, it will tend to dehydrate them, and make them sting. For long exposures to salt water, I’d recommend wearing swimming goggles, or a diving mask.

Question:

If whales are mammals just like us, why doesn’t salt sting their eyes?

Answer:

Whales and other animals that live in the ocean have evolved a very special kind of tear that contains mucus, making it much thicker, and protects them from the dehydration and other effects of the salt water.

Question:

Is opening your eyes in a pool harmful to your eyes?

Answer:

Opening your eyes in a swimming pool exposes them to dirt and other debris that might be floating in the water that could cause an irritation of the eye. It also exposes them to germs and to other bacteria in the water that could cause an eye infection. Swimming pools are filtered to remove any dirt, and they’re treated with chlorine and other chemicals, to try to kill any harmful organisms. However, some people are sensitive to the chemicals used in the pool and that could also irritate your eyes. A brief exposure to say, swim down and pick something up off the bottom of the pool is probably not going to be harmful, if the water is clear and reasonably well-maintained. But a longer exposure, or in water that’s more questionable, I’d recommend wearing swimming goggles.

Question:

Why does salt water in the ocean sting your eyes, but not your salty tears?

Answer:

There is a tiny amount of salt in your tears, but its minor compared to the amount of salt present in salt water. Your tears contain about 0.9% sodium chloride, while salt water in the ocean contains 3.5%! That means the oceans is almost four times saltier than tears.

Question:

Can you open your eyes in the ocean?

Answer:

It’s safe to open your eyes in the ocean, but it may sting at first. Many people become accustomed to salt water and they don’t feel pain when they open their eyes underwater.

The ocean also contains many different irritants like bacteria, sand, and microorganisms, so don’t forget to pack your goggles!

To learn more about your eyes, visit https://nei.nih.gov/kids