The Effects of Chlorine on Human Hair

Effects of Chlorine on Human Hair
Many years ago, I knew someone on a neighboring high school swim team quite well. She swam varsity her sophomore year, and it seemed like everything she did outside of school had to do with her swimming. Her schedule was full, and any time she spent with friends was heavily negotiated. Finally, long after I had first known her, she got a break from swimming for about a month, and the strangest thing began to happen.

Her hair began to change color.

She was very excited about it. Her hair was usually a dull blonde, with a faint green tint at the ends. Now it was darkening into a calm brown, with natural highlights beginning to push their way into the light. She would ask me many times about what I thought her hair looked like, and what I would do with that color of hair. Soon, however, swim practice began again, and in only a couple of weeks her hair began to fade.

I was puzzled. I knew what chlorine was, but I still wondered: How could it do this to her hair?

Chlorine 101

According to the Royal Society of Chemistry, chlorine is a nonmetal element that is found on the periodic table of elements, atomic number 17. It is not found by itself naturally, because it has a disposition to bond with other elements at its earliest convenience. It most commonly occurs as part of sodium chloride (NaCl), or table salt. It is also found in potassium chloride (KCl), and many other compounds where the negative charge of a chloride (Cl-) ion balances a positive charge in other ions. Chlorine was first discovered in 1774, when Carl Wilhelm Scheele heated hydrochloric acid (HCl) with manganese dioxide (MnO 2) and a greenish yellow gas began to fill the air. (The name for chlorine comes from the Greek word “chloros”, which literally means greenish yellow.) This gas bleached litmus paper, leaves and flowers. Chlorine is an intense respiratory irritant and is heavily toxic to humans, so much so that it was actually used in chemical warfare during the First World War. It’s also destructive to the ozone layer in the atmosphere, and just one atom of chlorine can destroy up to a hundred thousand molecules of ozone.


It sounds rather bad at this point, but here is one of chlorine’s redeeming qualities: It also kills bacteria. It’s commonly used as a disinfectant, and can be found in bleach. That’s why you can also find small amounts of chlorine compounds in your swimming pool, and in your drinking water. It’s included to keep you from becoming ill due to pathogens, and it has been used in water and sewer systems for over a hundred years. It has likely saved millions of people from becoming sick. Chlorine is also widely used in the manufacturing of paper, PVC, plastic, clothing, and many more consumer products. Evidence of chlorine’s presence is probably all around you at this very moment.

What Does It Do to Hair?

Floating in Pool

Chlorine dissolves when it enters water, becoming hypochlorous acid (HClO-), but it still has high bonding potential with other elements and compounds. If metallic substances such as sodium, potassium, or copper are found in the pool, the chlorine will attach itself to them and turn into salts (for the alkali metals) or other compounds, and if certain organic compounds are found in the pool, like segments of bacteria, chlorine will also bind itself with them. Similarly, when a human with skin, hair, and fingernails gets in the pool, the chlorine will be attracted to each of those things, particularly because of the oil in or on them.

According to, human hair is comprised of protein, mostly keratin. This hair is coated and infused with an oil known as sebum, which also covers the rest of your entire body. Sebum is a natural secretion which helps the body and the hair retain moisture, and which also contains the anti-aging antioxidant vitamin E. It’s an essential part of your hair and skin, and keeps your features vibrant and strong for a long time.

When hair comes in contact with chlorinated water, the chlorine will bond with this sebum in your hair and pull it out by chemical bond. This will leave your hair looking less shiny and less strong, and looking drier than usual during the day. If this continues, your hair will begin to split at the ends, and its condition will deteriorate.

No more boring swim laps! Enjoy music and audiobooks while swimming with the Syryn waterproof mp3 player. A woman who has just been swimming smiles while holding a Syryn and listening to audio.

Sebum is not the only thing that chlorine affects. Chlorine can alter the makeup of your very hair itself. When it encounters the keratin protein in your hair, it chemically bonds with some of the parts of the protein molecules and makes these parts water-soluble, causing the proteins in your hair to physically weaken and become thinner.

And remember the story from the beginning? Chlorine can indeed change the color of your hair. If it can make paper white and take the color out of flowers, then it should be no surprise that, over time, chlorine in the pool will bleach your hair. Chlorine reacts with the melanin in your hair that gives it color, from blonde to jet black. When this melanin is bonded to chlorine, the keratin protein is left behind in its natural dull blonde color. This is accelerated when hair is already not its natural color; dyed hair has chemical treatments in it that the chlorine will bond to readily. If your dyed hair was bleached at one point to achieve its current color, the artificial color will leave even faster in the presence of chlorine.

A common misconception, like mine a long time ago, is that the chlorine in the pool also causes hair to turn green. After all, it’s green as a gas, so why wouldn’t it be the culprit? Well, it isn’t true – at least, not directly. The green color is caused by the presence of copper in a chlorinated pool. When copper and chlorine meet, they usually create copper(II) chloride (CuCl2). However, when they meet in water, like a swimming pool, the molecules crystallize around water molecules, creating copper(II) chloride dihydrate (CuCl2(H2O)2), which is a compound that is notable for its bright blue-green color. This reaction can occur inside your hair when copper is in your swimming pool, and it will cause your hair to turn a pale green.

Copper chloride crystal

Copper(II) chloride dihydrate crystal.

Now That I Know What Chlorine Does, Can I Avoid It?

If you’re a regular pool swimmer, you’ll likely be unable to avoid chlorine completely. However, there are some things you can do.

  1. Rinse your hair with water before getting in the pool. Like, rinse it. A lot. According to cosmetologist Kendra Aarhus of, “Have you ever noticed that a sponge will only absorb so much water, and once it’s full the water just runs off? Your hair is similar to a sponge. If you saturate your hair with clean tap water, your hair will be less likely to absorb as much of the chlorinated water in the pool.”
  2. Apply a healthy amount of a pre-swim in-hair defense. AquaGuard is an example of a proven shield against chlorination. Apply it to your hair after rinsing and work it through to the ends to ensure even coverage. This is especially important for habitual swimmers; the oils in AquaGuard will replenish the oil losses already sustained by your hair.
  3. Use a swim cap. The chlorine won’t be able to reach 95% of your hair with a cap on your head. Swim caps are meant to reduce drag and increase speed during your swim, but this is a convenient side effect.
  4. Rinse immediately after you’re done, and then shampoo when you get home. The sooner you put water and soap through your hair, the more chlorine you’ll be able to run out of town. You can also buy special swimmers’ shampoo that will give an extra edge in getting the copper chloride out of your hair.
  5. Keep your hair strong. The best offense is a strong defense, after all. Be kind to your hair during the day. Eat foods with plenty of protein. Make sure to look for split ends and trim to avoid them. If your hair is its natural color, keep up the good work; you’re making chlorine’s job difficult. Don’t stress about it; just take care of yourself!

Use This Information

Hair is an important thing to most of us, and so are our skin, nails, and the rest of our body. There are worse things than hair discoloration, and that should be remembered (especially when suffering from it). However, knowing what chlorine does to your body is empowering and helps you to avoid inconvenience or even unhealthiness. It is also good to remember why chlorine is in the swimming pool – to keep you and your family safe from bacteria and other infectious pathogens. Chlorine will likely have an indispensable presence among us for decades to come, and most of us will continue to swim in pools with chlorine in them for years. Just remember these things, and you will be able to keep your hair as safe it can be.

Also, you will be able to know why that friend from school still has green hair after nearly half the school year.

No more boring swim laps! Enjoy music and audiobooks while swimming with the Syryn waterproof mp3 player. A woman who has just been swimming smiles while holding a Syryn and listening to audio.

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