Hydrogen peroxide is a common, affordable household cleaning and disinfecting product.

In an unopened bottle, hydrogen peroxide can last for around 3 years. However, once you open the container, it starts to break down quickly and lasts for a much shorter period of time.

Although expired hydrogen peroxide isn’t harmful, it’s not an effective disinfectant once it’s past its expiration date.

Let’s get into what hydrogen peroxide is, how long it typically lasts, and how to tell if it’s expired.

Hydrogen peroxide is an organic compound made up of two hydrogen (H) atoms and two oxygen (O) atoms.

Its chemical formula (H2O2) looks very similar to that of water (H2O). While these two compounds may look similar, they don’t share much in common.

Pure hydrogen peroxide is a pale blue liquid. It has a strong odor and is slightly thicker than water.

The hydrogen peroxide you purchase at the pharmacy is a solution, which means that a small amount — usually 3 to 7 percent — is dissolved in water. It’s colorless.

Hydrogen peroxide has several properties that make it an effective cleaner.

Firstly, it produces compounds known as free radicals, which attack and disable viruses and other pathogens.

Secondly, it’s also mildly acidic and has long been used to whiten paper, fabrics, and even hair and teeth.

However, these same properties mean that you need to use it with caution. It can cause irritation if it comes into contact with your eyes, skin, or throat.

Hydrogen peroxide has many uses, both inside and outside of the home.

In your home, it can be used to clean and sanitize. You can use it in the kitchen to:

  • clean your dishwasher
  • disinfect surfaces
  • wash germ-prone trash cans and sinks

In the bathroom, a little bit of hydrogen peroxide goes a long way in cleaning your:

  • toilet
  • shower
  • bathtub
  • mirrors
  • countertops

Many people also use hydrogen peroxide to remove stains and brighten white garments.

Outside of your home, hydrogen peroxide is widely used in a number of industries, including:

  • healthcare
  • food production
  • beauty
  • manufacturing

It’s also added to products, such as:

  • hair dye
  • bleach
  • toothpaste
  • mouthwash

Hydrogen peroxide is relatively unstable and decomposes quickly.

In a sealed container, hydrogen peroxide lasts approximately 3 years. However, as soon as you open the container, it starts to break down. You might be surprised to learn that it’s only effective for 1 to 6 months once the container is opened.

To ensure it lasts as long as possible, store hydrogen peroxide in a cool, dark place. Don’t open it until you need to use it, and when you do open it, keep it in the original brown bottle. The bottle is designed to prevent light from making it decompose faster.

When you’re using it, make sure the liquid that’s left inside the bottle doesn’t come into contact with anything else. For example, don’t dip your finger or a rag into the bottle. This could make it decompose faster.

Hydrogen peroxide becomes less and less effective over time. In fact, it starts to decompose even before you open it. In a closed container, it’ll eventually break down into water and oxygen gas.

When the oxygen gas escapes through the top of the container, only water is left in the container. Of course, water isn’t an effective household cleaner or disinfectant.

Hydrogen peroxide is a pretty reactive substance, so there’s a simple way to detect whether it’s still good. Simply pour a little of the liquid into your sink and watch to see if it fizzes or bubbles. If you don’t notice anything, it’s likely no longer good.

You can dispose of expired hydrogen peroxide that you bought from a pharmacy by pouring it down the sink. Higher concentrations of hydrogen peroxide need to be diluted with water before they’re thrown out.

Even low-concentration hydrogen peroxide that you buy at the pharmacy poses some risks.

When using it to clean inside your home, make sure the area is well-ventilated. If you can’t open a window or ensure proper air circulation, wear a mask to avoid inhaling it.

Hydrogen peroxide can irritate and even burn your skin. To avoid getting it on your hands, wear gloves when using it. If you get some on your hands, wash your hands immediately with soap and water and rinse them under the tap for several seconds.

Also take care not to get it in your eyes, as it can cause irritation and in severe cases, eye damage. If you get some in your eyes, flush your eyes with water for at least 15 minutes.

It’s not safe to ingest hydrogen peroxide. For this reason, it’s important to store it in a safe place where children and pets can’t access it.

In case of an accidental ingestion, call the Poison Control helpline at 1-800-222-1222 or use the online tool to determine whether you should seek medical attention. In case of an emergency, always call 911.

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Hydrogen peroxide is a chemical substance that has many uses around the home. It can be used as a surface disinfectant, stain remover, and bleaching agent.

An unopened container of hydrogen peroxide will last for around 3 years, but as soon as it’s opened, it’ll expire within 6 months.

You can check to see if hydrogen peroxide is still good by pouring a small amount down the sink and looking to see if it bubbles or fizzes. If it doesn’t cause this reaction, it’s likely no longer good.