There are 10.4 million residential swimming pools in the US.

The majority of those pools will be cleaned using chlorine, a disinfectant that destroys and deactivates germs. The American Chemistry Council writes that chlorine’s disinfectant qualities come from its ability to bond with and destroy the outer surfaces of bacteria and viruses. Chlorine has the power to clean and sterilize swimming pools, along with hospitals and hotels, but it can also affect your body.

INSIDER spoke with dermatologists to determine what chlorine really does to you.

Chlorine is extremely drying to the skin.

Pools are perfect for cooling off and beating the heat. Being in the water doesn’t mean your skin is being hydrated, though. Chlorine is known to dry the skin, and some people may also find their skin feeling scratchy or irritated by it, too.

“Chlorine is extremely drying to the skin,” Dr. Debra Jaliman, an American Academy of Dermatology Spokesperson with a private practice in New York told INSIDER. “It’s especially important to take a shower right after getting out of a chlorine pool.” She also advises putting on moisturizer to replace essential oils that chlorine can strip away from skin.

Chlorine can make your hair brittle or fragile.

In the same way that chlorine can dry out hair, it can dry skin. Letting your hair sit in chlorine water can do damage to your locks.

Dr. Adam Friedman, Associate Professor of Dermatology and Director of Supportive Oncodermatology at George Washington School of Medicine and Health Sciences, says that it can also make hair brittle. On Columbia University’s website Go Ask Alice, where health professionals answer anonymous questions, the team answered a question about the impact of chlorine on hair. According to their response, chlorine sucks sebum (oil secreted from your glands) out of your hair. “[This] may cause the cuticle to crack,” the team wrote. “This damage causes your hair’s natural sheen to diminish, and the unprotected cortex to potentially ‘split,’ creating split ends.”

Those with color-treated hair have often been told to be especially careful when swimming in pools, but Friedman said that it’s not chlorine that sometimes turns color-treated hair green. “While swimming in a swimming pool has been known to turn hair green, it is actually the copper in the pool, not the chlorine, that does this,” he told INSIDER.