Bleaching hair twice with 20 vol, good or bad idea?

dark roots bleached hair


  • You can bleach your hair twice with 20 vol, but not twice in a row. Not even twice in a week.
  • To bleach your hair twice with 20 vol, you must let your hair breathe for at least one or two weeks.
  • If you bleach your hair twice in a row with 20 vol, you’ll damage it. It would be like applying 40 vol directly to your mane.


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If you’re reading this, it’s because you’re not a professional colorist.

So, I encourage you to take things slowly. Bleaching is a complex chemical process that involves many elements.


It has to do with chemicals, bleaching agents, and your hair health.

Trust me when I tell you that when bleaching goes wrong,   often the only solution is to cut the hair to remove the burnt parts.  


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Yes, you read that right. I wrote “burnt.” When you bleach your hair a few times in a row without allowing it to rest, you damage your hair.

I know what you’re thinking, ” Alejandra, my friend Juanita got two bleaching sessions in a row one day. She told me she could do the same thing if she used 20 vol.”


  I’d advise you to tell your friend Juanita that she shouldn’t give her friends advice that she doesn’t follow. In the end, she bleached her hair in a salon.  

You can also tell her that the hairdresser probably used products like Olaplex to protect her hair during the process.


It’s a way of shedding light on the matter.

After all, if your friend isn’t a hairdresser, she shouldn’t give advice on topics she doesn’t know about.

Do I seem angry?


Actually, I’m not.

Sometimes I worry about the things people do to their hair without caring for the consequences.

If you’re thinking about bleaching your hair twice with 20 vol, the least I can do is explain the two-parts process your hair will undergo.


Once you understand the process and the consequences, you can make your best decision.

Are you still there?


My heart sighs in relief.

So, let’s start at the beginning.


What happens to your hair when you bleach it twice with 20 vol?

lighten hair slightly

Bleaching is the process of changing the shade of your hair to a lighter one. Bleaching agents are used in the process: a developer or hydrogen peroxide, and bleach powder or ammonia.


You can only get a certain level of lightening done.  Expect to get at least three shades lighter per bleach with 30 or 40 vol.

Of course, this isn’t so simple because bleaching weakens the hair and dries it out.



To remove the pigments, the chemicals penetrate the hair core to alter its structure.

That’s how bleaching works with a 30-volume developer.

  Then, why would you want to use 20 vol two sessions in a row?   


I can think of two possible reasons.

  • You think that if you bleach twice with 20 vol, you’ll damage your hair less.
  • You think that if you do two sessions with lower volumes, the color change of your hair will be more subtle.


Unfortunately, those assumptions are far from the truth.

While a 20-volume developer is less damaging to the hair than a 30 or 40-volume developer, it also dehydrates your hair.


Also, you’re thinking of having two bleaching sessions with 20 vol. So, let’s do a simple calculation:

Bleaching with a 20-volume developer + bleaching with a 20-volume developer = 40 vol.

Do you get the picture?


  Finally, your hair will be exposed to a chemical reaction of 40 vol.  

Wouldn’t it be better to bleach with a 30-volume developer?


  If you use a 30-volume developer in a single session, you’ll achieve a uniform color and be able to lift more shades.  

On the other hand, you’ll protect your hair by doing one single session.

Take into account these details before bleaching if you don’t have bleaching experience.


In addition to this, the darker your base color, the more bleaching sessions you’ll need to achieve a light or extra light blonde.

Now tell me the truth. Have I convinced you to do a single bleaching session using a 30-volume developer?


I know most of you will answer yes because you’re considering what’s best for your hair.

But I’m also convinced that there’re people who want to experiment.

Therefore, the information I’ll provide below will be for those who know why they want to bleach their hair twice with 20 vol.

For those people, I have a piece of advice. It’s perhaps the most important one.


If you want to bleach your hair twice with 20 vol, you should wait at least one week between each session

even bleaching process

There’s no room for doubts here.





What do you need?

  • Bleach powder
  • 20-volume developer
  • Plastic container
  • Dye brush
  • Gloves
  • Hair clips
  • Coconut oil for added protection


You can also apply the oil from roots to ends the night before and don’t rinse it before bleaching.


  • Step 1: prepare your hair

Comb and separate your hair into four sections, from forehead to nape and from ear to ear, holding each section with hair clips.

I recommend that you stop washing your hair the previous 48 hours for the scalp’s natural oils to protect it.


  • Step 2: preparing the bleach

In a plastic container, place the bleach powder and the 20-volume developer. Mix to integrate.

Once you have achieved a creamy consistency without lumps, add coconut oil.


  • Step 3: Apply the bleach

Release one of the sections and with gloves on, apply the bleach from roots to ends.

Repeat on each section. After saturating your hair, place a shower cap or nylon bag to maintain the temperature of the reaction.


LEAVE THE BLEACH TO PROCESS FOR 20 TO 30 MINUTES. Never leave it on longer than thirty minutes because the chemical reaction stops. Therefore, your hair will no longer bleach. Instead, the chemicals will still dry out your hair.


  • Step 4: Rinse and dry

Rinse your hair with plenty of cold water. Let the water run over your hair for at least three minutes. You can use your regular shampoo to remove any remaining bleach mixture.

I recommend that you apply the conditioner and leave it on for about five minutes to allow your hair to absorb all the nutrients.

So far, you have applied the first bleach.




You should wait at least one week to moisturize your hair and prepare it for the next application.

You can use coconut oil as a moisturizing mask. Leave it on overnight and rinse it out in the morning.

After one week, repeat the application following all the steps above.



As a professional hairdresser, my advice is that you bleach your hair with 30 vol instead of applying two sessions in a row with 20 vol.  

While the 20-volume developer has a lightening effect, it may not be enough to lift the hair cuticles and remove the pigments in the hair core.

Also, the damage caused by a 20-volume developer is cumulative. So, two bleaching sessions in a row with 20 vol is equivalent to a single session with 40 vol.

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