What Is Bleach? How Bleach Works

While the word "bleach" entered the English language around the year 1050, bleach containing sodium hypochlorite was first manufactured in the U.S. in 1913, for use as an institutional disinfectant and a water treatment.

Before that, chemicals such as borax, ammonia and lye were the most common bleaches in the U.S., and bleaches made using chlorine were generally too expensive to manufacture until the 20th century.

Clorox Chemical, later called the Clorox Company, first gave samples of bleach to consumers for household use in 1922. Since chlorine bleach was faster and more effective than the bleaches people had been using, it quickly became the most popular household bleach.

Today, when we say "bleach," we usually mean a chlorine bleach solution.

There are two main classes of household bleach: chlorine bleaches and non-chlorine bleaches (aka oxygen bleach).

All of these bleaches are in a class of chemicals known as oxidative agents, meaning that they cause a chemical reaction called oxidation when they come into contact with certain stains, certain germs or other organisms, and sometimes clothing dyes.

Chlorine bleach contains the active ingredient sodium hypochlorite (NaOCl), while non-chlorine bleaches have different active ingredients for different purposes.

Hydrogen peroxide, for instance, is common in color-safe bleaches, and sodium percarbonate or sodium perboate are typically used in "oxygen power" stain removers.

So what, exactly, happens to that ketchup stain on your white T-shirt when you bleach it? In order to understand how chlorine bleach makes a stain "disappear," we need to understand how colors work.

How Colors Work

Light is both a particle and a wave; its particles, called photons, travel in waves that have a particular length.

Not all wavelengths of light are visible to the human eye: Infrared light wavelengths are too long for our eyes to see, and ultraviolet wavelengths are too short. The wavelengths we can see are between 400 and 700 nanometers, and they appear as color to us.

For example, when light with a wavelength of about 475 nanometers hits the retina in your eye, you perceive the color blue. The light that comes from the ketchup stain on your T-shirt to your retina has a wavelength of about 650 nanometers, which makes it appear red.

The Chemical Makeup of a Stain

The reason the ketchup stain reflects light with a wavelength of 650 nanometers has to do with its chemical makeup. Like most other substances, ketchup is made up of multiple elements joined together by chemical bonds to form molecules.

The electrons involved in some of these bonds are capable of absorbing light of certain wavelengths, depending on the characteristics of the chemical bond. The light that the electrons in a substance can't absorb determines the substance's color.

So the ketchup stain is absorbing all of the wavelengths of normal light that hit it — except the 650 nanometer light, which it reflects back to your eye, making it appear red.

How Chlorine Bleach Makes Stains 'Disappear'

Many stains have a network of double bonds between carbon atoms, and this network absorbs light. Chlorine bleach solutions can oxidize many of these bonds, breaking them and taking away the substance's ability to absorb light.

When this happens, the stain "disappears." When bleach oxidizes the ketchup on your T-shirt, the ketchup stops being able to absorb light. It then appears white, like the rest of the shirt.

The remains of the ketchup can still be there; you just won't see the stain anymore. Soaking and washing the shirt can remove the now-invisible stain.

Why Does Bleach Take the Color Out of Clothes?

Since sodium hypochlorite is a powerful oxidizing agent, it is able to oxidize chemical bonds not only in stains on your clothing, but also in the dyes that give the clothing its color.

Anyone who has accidentally dripped chlorine bleach on their favorite pair of jeans has experienced just how effective bleach is as an oxidizing agent.

A non-chlorine bleach that uses a weaker oxidizing agent, such as hydrogen peroxide, can break the chemical bonds in certain stains without breaking the stronger chemical bonds in clothing dye.

The use of chlorine bleach as a medical disinfectant was first recorded in Austria in 1847. Staff at the Vienna General Hospital began using it to keep "childbed fever," a severe infection that killed countless women after they gave birth, from spreading throughout the maternity ward.

It's now used to disinfect dialysis equipment, some surgical equipment, surfaces in hospitals and medical labs, and even some medical waste.

The food processing industry uses chlorine bleach to kill hazardous bacteria such as Listeria, Salmonella and E. coli on equipment. Sodium hypochlorite also is added to municipal drinking water to kill dangerous waterborne organisms like the bacterium Salmonella typhi, which causes typhoid fever and killed many people before water disinfection and antibiotic treatment became common.

Chlorine bleach kills Vibrio cholerae, the bacterium that causes cholera, a disease that killed in epidemic proportions before water treatment. It can still kill in countries where clean drinking water is not available.

Chlorine bleach can also kill dangerous bacteria and viruses on surfaces, such as methicillin-resistant Staphylococcus aureus (MRSA), influenza and HIV. Chlorine bleach is especially valuable as a disinfectant, since germs are not able to develop immunity against it, as they have done against certain drugs.

How Chlorine Bleach Kills Germs

To kill germs, sodium hypochlorite uses the same quality that makes it such a great stain remover — its power as an oxidizing agent. When sodium hypochlorite comes in contact with viruses, bacteria, mold or fungi, it oxidizes molecules in the cells of the germs and kills them.

Scientists also believe that the hypochlorous acid that forms when sodium hypochlorite is added to water can break down the cell walls of some germs. The hypochlorous acid also seems to be able to cause certain proteins to build up in bacteria, making their cells unable to function.

Non-chlorine bleaches that are oxidizing agents can also act as disinfectants on some surfaces, but they are less potent than chlorine bleach. Chlorine bleach, when used properly, is a practical and effective disinfectant.

Hospital personnel use bleach as a disinfectant, hotels use bleach to clean and disinfect bed linens and surfaces, and restaurants disinfect food preparation surfaces with chlorine bleach.

People use chlorine in swimming pools to keep the water clean and raise the pH, and in much smaller concentrations to help keep municipal water supplies free of harmful organisms.

Companies sometimes add chlorine bleach to industrial wastewater to reduce odor, and chlorine is used by the glass, chemical, pharmaceutical, textile, agriculture, paint and paper industries.

With its many uses, bleach its a very familiar product to most people. But when did we start using this chemical?

Since chlorine bleach is a strong oxidizing agent, it's hazardous if not used properly. You should never mix chlorine bleach with any other household chemicals, because it can react to form very hazardous substances.

For example, mixing bleach with ammonia or vinegar can release poisonous chlorine gas. Cleaning and disinfecting products that aren't called "bleach" may also contain sodium hypochlorite as one of their active ingredients, so you should always read the label before using a cleaning product.

How to Safely Disinfect Surfaces

If you are using bleach to disinfect household surfaces, make sure the area is well ventilated and do not inhale any fumes. Fumes from chlorine bleach can cause coughing, sore throat and airway irritation, and it can also irritate the eyes.

Keep chlorine bleach from coming into contact with your skin, since it can cause redness and irritation, especially after repeated exposures. If bleach gets in your eyes, rinse them immediately and call your doctor.

Ingestion of chlorine bleach can be very dangerous, especially to children. If you or your child accidentally swallow bleach, don't induce vomiting. Call the Poison Control Center immediately at 1-800-222-1222.

How to Safely Use Bleach for Laundry

When using chlorine bleach for laundry or cleaning, you should dilute it.

For whitening white clothing, The Clorox Company recommends washing the clothing on the hottest setting recommended on the fabric label and adding 3/4 cups (177 mL) of bleach to the wash. Certain fabrics, such as mohair, wool, silk and Spandex will be damaged by chlorine bleach, so always read the clothing label before bleaching.

For colored garments, you can use a "bleachability test" on a non-visible, colored part of the garment. Mix 2 teaspoons (10 mL) of bleach with 1/4 cups (59 mL) of water, and put a drop of the solution on a hidden part of the fabric. Wait one minute, blot with a towel and check for any color change.

For pre-soaking a white item of clothing, you can mix 1/4 cups (59 mL) of bleach with one gallon of water and soak for 15 minutes before washing.

For disinfecting clothes, pre-soaking with chlorine bleach and washing in hot water with chlorine bleach is effective, but washing with non-chlorine bleach is not adequate, because active ingredients like hydrogen peroxide aren't powerful enough to disinfect laundry.

For disinfecting dishes or hard surfaces, use a solution of 1 tablespoon (15 mL) of chlorine bleach mixed with 1 gallon (3.8 L) of water.

The Environmental Protection Agency (EPA) has evaluated multiple scientific studies on the effects of chlorinated drinking water, and the organization's found no evidence of risk for cancer, reproductive problems or birth defects.

The European Commission (EC) also determined that the most common sources of exposure to chlorine bleach is through skin contact when using bleach for cleaning at home or through ingestion of chlorinated drinking water.

Swallowing small amounts of swimming pool water may also be a risk, but there is no significant indirect exposure through the environment. The Commission determined that there is no evidence of negative health effects due to long-term exposure to small amounts of chlorine bleach.

According to the Centers for Disease Control's Agency for Toxic Substances and Disease Registry, when sodium hypochlorite is released into the air, it's broken down by sunlight and natural substances in the environment.

Sodium hypochlorite does not accumulate in the food chain like some substances do, such as mercury. When sodium hypochlorite gets into water or soil, it breaks down into the ions sodium, calcium and hypochlorite; these ions can potentially react with other substances in water, but the possible effects are not known.