How Long Does Hair Bleach Last After It’s Mixed?

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Bleaching is an important step if you have darker hair and want a lighter color. However, bleaching can be damaging to your hair. It is important to take precautions when using it.

Although it is best to go to a professional to have your hair bleached, that’s not always feasible.

And some also love the challenge of doing things on their own! If that’s you, you might ask How long does hair bleach last after it’s mixed and on your hair?

Hair bleach can remain active for about 20 minutes to about 45 minutes. That will depend on the brand and formulation you get. 

Timing is very important to bleaching.

We’ve all heard about people who damaged their hair because they left the bleach on for far too long or they used an old mixture. 

Let’s avoid that!

In this article, we’ll explain why that can happen and we’ll guide you with the proper timing when it comes to bleaching your hair. 


How Does Hair Bleach Work?

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In order for us to figure out how long hair bleach would last, we first have to know what happens when we mix them and how it effectively bleaches the hair. 

Hair bleach can come in different formulations. Usually, the main active ingredient is hydrogen peroxide. But there can be other formulations too. 

Regardless of the formulation, the reaction it does to bleach the hair is similar. First, the alkaline mixture will open up the cuticle. This allows the product to get into the core of the hair where the melanin, which colors the hair is present. 

The melanin, which is now exposed to the oxidative agents, will dissolve the natural pigment. The longer the bleach is exposed to the hair, the more bleach it becomes. 

However, you should still take note of the maximum time you can leave the bleach on your hair.

Even if you want to bleach your hair as light as it can be, prolonged exposure will just damage it. 

If your hair is dark and you want to really lighten it, it may take several bleaching sessions for you to reach the lightness that you want to achieve. Make sure not to do it consecutively or else your hair might fall off.

If you really want to bleach your hair again, it is best to wait for 15 days before bleaching it again. Additionally, in between those bleaching, you should be applying hair products that will deep condition the hair and rehydrate it

Remember that bleaching will damage your hair no matter what. The extent of the damage will vary and you definitely wouldn’t want to risk your hair being mushy and breaking off with too much bleaching. 

How Long Does Hair Bleach Last On Your Hair?

When hair bleach is prepared, you should put it on your hair immediately after mixing it. The reaction between the two will effectively remove the color of your hair. 

Typically, hair bleach is only placed on hair for up to 20 minutes. The first twenty minutes is when the solution is most potent and could actively bleach the hair.

After that, the bleaching action slows down but it still continues to damage the hair the longer it stays in the hair.

Some can extend the exposure on the hair for up to 30-45 minutes. But that also increases the risk of further damage.

Remember that applying bleach already damages the hair as it removes the color. Prolonging the exposure damages it further. 

The chemical product is harsh, it could dry up your hair and eventually lead it to break and fall off.

I think we are all familiar with videos of bleaching gone wrong. Usually, those who experience it apply the bleach for far too long.

Aside from damaging the hair, the bleaching solution can also irritate the scalp.

How Long Can Hair Bleach Sit After It’s Mixed?

Hair Bleach Powder

Hair bleach usually comes in two parts, a liquid one and a powdered one. They are separate from each other when you buy them because the reaction of the two parts is what efficiently bleaches the hair. 

That is why you can’t use premixed hair bleach. Hair bleach, when mixed, can only last for about 45 minutes.

You have to apply it immediately when you mix it.

It is not a good idea to use hair bleach that has already been mixed beforehand because the reaction between the ingredients is already complete. It will not bleach the hair and will just damage it. 

Can You Save Hair Bleach After It’s Mixed?

If you have leftover mixed bleach, all you can do is throw it away. You can’t store it for future use. If you think you have a lot of hair bleach and wouldn’t use it all, don’t mix more than you need.

If you have leftover mixed bleach, all you can do is throw it away. You can’t store it for future use. If you think you have a lot of hair bleach and wouldn’t use it all, don’t mix more than you need.

It is possible to save up some hair bleach if you keep the ingredients separate and store them properly. But if you’re not careful, just pick up some new bleach when it’s time to bleach again.

Does Hair Bleach Powder Expire?

Hair bleach powder does expire, most powder bleaches will have an expiration date printed on the tub. Typically it will last for about a year after opening, and three years unopened. And when it is expired, you should discard it and not attempt to use it anymore. 

If yours doesn’t have a date on the package, write down the date when you first open your bleaching powder. 

Although the opened bleaching powder still has a long expiration (about a year) you need to store it properly to avoid it from prematurely deteriorating. If not, the powder could change and you may need to discard it before the expiration. 

There are a few signs to watch out for to determine if you should dispose of the bleaching powder, even if it hasn’t reached the expiration date. One of them is the consistency of the product. 

If the bleaching powder looks like wet sand, you should discard it. It probably got wet due to contamination or due to moisture. Bleaching powder is activated when mixed with the liquid developer so getting it wet is not good. 

If you open the tub and you get irritated with the scent of ammonia or your eyes become watery, then you should throw it out. That’s because the ammonia content has already reacted while it was in storage. 

Final Thoughts

In order to create a hair-bleaching solution, you usually have to mix two parts. The two parts are separated because the reaction between them is what removes the colors from the hair.

That means that you have a limited time to use the hair bleach when it is already mixed. 

Once the hair bleach solution is already prepared, you have to apply it immediately to the hair. Depending on how light you want to go, most experts advise leaving it on the hair at a maximum time of 20 to 30 minutes. 

Although some may extend the time to up to 45 minutes, that will also increase the risk of damaging the hair further.

The bleaching process naturally damages the hair and prolonged exposure to it damages it further. 

Once the hair bleaching solution is mixed, you can’t keep it for future use. Once the 45 minutes is up, it won’t effectively bleach your hair but just damage it due to the harsh chemicals in it. 

Written by Kayla Young

Kayla is the founder of LuxeLuminous. She has worked professionally in the tanning industry for years. She has been interested in esthetics since childhood, and has tried every hair, skin, and makeup product ever produced (more or less).