What happens if you leave hair dye in for an hour? Any of the following…

leave hair dye for more than an hour

If you leave hair dye in for an hour, some of these things can happen, in the best-case scenario, or all of them, at worst:

  • You may saturate your hair with color molecules, and the dye will last less.
  • Your hair may become brittle and damaged.
  • You may experience an allergic reaction on your scalp.
  • The color may become uneven.


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Does hair dye get darker the longer you leave it in?


As you can see, none of these things is good.

Sure,  if you leave hair dye in for an hour, and your color lasts less, it’ll be less dramatic than if you leave it in for an hour and end up with broken hair or a damaged scalp. 


However, appealing to your conscience and common sense, I ask you:

Why would you want to leave the dye in for an hour? What are you looking for?

  • You won’t be listed in the Guinness book of records as someone who can withstand the most hair dye. That record, thank God, doesn’t exist for now.
  • Your color won’t be more intense. If you choose to dye your hair light brown, it’ll be that color even if you leave the hair dye in for an hour.


Above all, why would you want to leave the dye in for an hour, if the manufacturers recommend  maximum exposure time is 45 minutes? 

some hairdressers hate box dyes

The truth is that hair dye manufacturers invest a lot of time and money to bring their products to market. Why do they invest time and money?


Because they invest hours of testing in their labs to find out how their product works on the hair, how long it takes to achieve the desired results, and what consequences may arise if the dye isn’t used as instructed.

That’s the key.


When you buy a hair color kit, you find the instructions inside, along with the dye bottle, developer, gloves, and post-color treatment.


The instructions explain how to apply the dye and the exposure times.

 Most manufacturers are very clear: the dye should be in for a maximum of 45 minutes. 

Why do you want to challenge that?


It’s great to be courageous in other situations in life. But in the case of dye exposure, your hair is out for damage.

Do you want to know why?

Let’s analyze one by one all the things that can happen if you leave the dye in your hair for an hour.

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If you leave the dye in for an hour, the color will last less time

what happens when the dye is left for less than an hour

Yes, it’s that simple. And it’s true whether you use a semi-permanent or a permanent hair dye. 

Let’s see why.


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The semi-permanent hair dye is deposited on the outside of the hair. Therefore, the only thing you’ll get if you leave the semi-permanent dye in for an hour is an excessive color on the hair.

 When you wash your hair for the first time, you’ll lose all the excess and the result will be a faded color. 


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Although permanent hair dye works differently, if you leave it in for an hour, you won’t extend the duration of the color either.

When your hair absorbs the pigments, they’re deposited in the innermost layer through the cuticles.  And your hair can only absorb so much pigment.


It doesn’t have a place to store pigments to extend the duration of the dye. Once your hair has finished absorbing the maximum amount of pigments, the coloring process is complete.


Therefore,  the color won’t last any longer if you leave the hair dye in longer than 45 minutes. 

Also, your hair won’t be the same either. That brings us to the second thing that can happen if you leave the dye in for an hour.

Your hair will be brittle and damaged if you leave the dye in for an hour

leaving the dye longer can damage the hair

The permanent dye needs a certain time to work. Like any product that performs a chemical reaction, it follows certain timings.

It takes 20 minutes for the permanent dye to open the cuticles and another 25 minutes for the color to settle.

 The chemical reaction stops after 45 minutes and starts leaving chemical residue on the hair. So, your hair starts absorbing that waste. 

Can you imagine what will happen to your hair if you leave the dye in for an hour?


The waste, which is the residue of ammonia and peroxide, will work against moisture and nourishment. It means your hair will become drier and weaker.

When hair is dehydrated, frizz appears. And when hair is weakened, it breaks when you comb or detangle it.


 Also, if your hair was damaged before applying the dye, it’ll worsen. Your hair could break at the roots, for example. 

I think I was pretty clear. The rest is up to you.

Leaving the dye in for one hour may cause an allergic reaction on the scalp

dermatitis on the scalp due to leaving the dye longer

Your scalp’s skin is as sensitive as any other area of skin on your body.

We already said that permanent hair dyes contain chemicals like ammonia and developer.

And some semi-permanent hair dyes may be made with paraphenylenediamine, also known as PPD.


 All the chemicals used in hair dyes may cause an allergic reaction on the scalp

Therefore, to minimize the risk, manufacturers recommend a maximum application time.

And that time should never be over 45 minutes.

The color could be uneven if you leave the dye in for an hour

Please, pay special attention here if you’ve bleached your hair previously.

In that case,  your hair will be porous. Then, the color could turn darker at the ends and lighter at the roots if you left the dye in longer than suggested. 


As regards semi-permanent dyes, you could leave the dye in longer than recommended by the manufacturer. The results will depend on the color you choose.

For example:

  •  If you apply fuchsia and you want a pastel color,  you should leave it for 20 minutes.
  •  However, if you apply fuchsia and you want a very intense color, , you could leave it for one hour.


But these results will depend on the color you choose. Some colors can be left in for longer to obtain more intense tones. Other colors won’t turn more intense if you leave them in longer.


After everything I’ve told you, I think the conclusion is more than obvious: you should never leave the dye in longer than what the manufacturer suggests.

If you use a permanent dye, that recommended time will always be 45 minutes, which may seem almost the same as an hour, but it’s not. If you leave the dye in for an hour, that fifteen-minute difference could seriously damage your hair.

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