How long does hair bleach last after mixing? Can you save it?

to apply to her roots

  • Once you prepare the bleach, you can only use it for a maximum of 60 minutes.
  • After that, it won’t have the power to lighten your hair, and, what’s worse, you´ll seriously damage the hair fiber if you use it.
  • The only thing you can store longer are the ingredients of the bleach mixture: peroxide and bleaching powder, separately. And I’ll tell you how to do it properly later on.


I know that these are difficult times and savings are essential.

Tell me about it. I have children and, lately, I´ve been showing off my cooking skills.

My grandmother used to call it “cooking the leftovers,” and that now the best chefs in the world have renamed, “Leftovers Recipes.”

So, I understand that you want to keep that leftover bleach mixture.


But watch out!

You’ll be playing with fire, and I mean that literally.

Have you ever thought about what bleach contains that makes it look so harmless to your eyes?


It has abrasive chemicals which, when used properly, are not dangerous. However, misused, stored, or incorrectly applied to the hair, they can damage your hair fiber.

 I’ll say it once: the leftover bleach should be thrown away! You should throw it away. It’s that simple.  


I think it won’t leave you bankrupt to discard that leftover bleach, after all.

Here I´ll be clear, and I won’t tell you “do what you want and face the consequences.” Because the consequences can be very negative for your hair, don’t you believe me?


Let me tell you Noelia’s story.

Noelia had bleached her hair. To tell you the truth, she had taken every precaution.


She had used 30-volume developer, added coconut oil to the bleach to minimize damage to her hair and respected maximum exposure times.

After a fortnight, she decided she wanted to lighten some parts of her hair further to create some light around her face. So, what did she do?


As she had some bleach leftover from her first bleaching, she decided to use it for some highlights.

She noticed that the mixture’s consistency was different from the one she had when she first used it. However, she went ahead.


 The results were bad because she made two mistakes: she used leftover bleach and used it for a second bleaching after fifteen days. 

The strands in which she applied the bleach she had saved became weak and brittle. I had no choice but to trim those locks.

Luckily, she hadn’t used that leftover bleach on all her hair. Otherwise, I would still be listening to her crying!


Listen to me!

Don’t keep any bleach leftovers. Stay with me and I’ll tell you:

  • How long bleach lasts
  • How to store bleach ingredients

Tabla de Contenidos


How long does bleach last?

30 volume developer and shampoo

Bleach has 2 ingredients:

  • Developer or peroxide
  • Bleaching powder or ammonia


 Both are very corrosive chemicals for hair, and you must be very careful in their preparation, storage, and usage. 


Once you mix them to apply the bleach to your hair, that mixture has two stages of reaction:

  • The primary and most clarifying reaction lasts 20 to 25 minutes.
  • The secondary reaction lasts 40 minutes


This means that your hair will be bleached very powerfully for the first 20 to 25 minutes. Then, it will continue to lighten steadily.


To help you understand it better, I’ll give you an example:

  • If you want to bleach your hair brown 4, when you apply the mixture for the first 20 minutes, your hair will lighten 2 shades. After that primary reaction, and for the next 40 minutes, the mixture will lighten your hair half a shade.


  It is for this reason that bleach cannot be stored for more than sixty minutes. It wouldn’t have a lightening effect on your hair. What it will do is weaken and damage it.  


Also, the chemical reaction generates heat, and that heat produces vapors, which can also be very harmful to your health.

Have you ever left bleach on your hair for more than 60 minutes?


If you left the bleach for more than 60 minutes, you would notice how it begins to grow and change its consistency from thick to foam.

Do you know why that happens?


Because the chemical reaction has stopped and, as a consequence, it has no more lightening effect.

That’s why you only have to prepare bleach at the moment you´ll use it. And if you have any leftovers, you have to throw it away. It is that important.


Now, what you can keep is the excess of peroxide and bleaching powder. But you must always store them separately, and I’ll tell you for how long and how.


How to store bleach ingredients separately for reuse

Remember that both peroxide and ammonia are chemicals?

For this reason, you must be very careful in their storage.


  • If you bought the peroxide or developer and never used it, you can keep it for up to 2 years.

It must be stored far from the sun and extreme temperatures.


But you must make sure that the lid is well sealed so that nothing can leak in it and degrade the peroxide.


  • If you have opened the container of bleaching powder or ammonia, you can keep it for up to one year.

Of course, that time will depend on the correct storage conditions. Therefore, you should keep it away from direct sun or humidity.


Bleach forms a very powerful chemical that not only lightens the hair but can also irritate your skin and hands. So, proceed accordingly to avoid further damage.



Before applying bleach, you should always ensure that the two ingredients, peroxide and ammonia, are in perfect condition.

Remember, bleach generates a chemical reaction that lasts 60 minutes. After that, the chemical components begin to degrade, and the bleaching effect is lost.

You should never keep the remains of bleach because it won’t do its job. What is worse, it can cause irreversible damage to your hair.

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