What happens if you leave hair dye in too long

Indeed, hair dyeing is the go-to when it comes to a subtle hair transformation. It’s easy and convenient.

But sometimes, dyeing your hair at home can get a little intimidating. 

Even selecting the perfect shade is a challenge. And most, if not all, also overlook a crucial detail — how long should you leave hair dye sitting? 

Is it okay to leave it overnight? What about leaving it for a shorter time? 

Clueless? That’s okay! 

Most people can’t answer these questions either. But don’t worry, this article is here to answer all that. 

So read along to know how long you can leave hair dye sitting and what happens if you leave it in for too long. 

Ready? If yes, let’s begin! 


How long can you leave hair dye sitting?

How long can you leave hair dye sitting

Permanent hair dyes 

Permanent dyes have potent chemicals, so leaving them too long may damage and dry out the hair, especially if you have thin strands. So, how long should you leave them? 

Generally, you should only leave them on your hair for 30 to 45 minutes. But this time frame also depends on several factors, such as your hair color, hair condition, hair thickness, and hair porosity. 

1. Hair color

The process is quicker if your desired hair color is similar to your original hair color. For example, you originally have brown hair and plan to apply a light brown dye. In this case, you’ll need the least amount of time. 

But if your hair is originally black, you’ll have to wait a little longer. 

2. Hair condition 

Unprocessed hair easily absorbs new pigment than chemically treated hair. Hence, you may leave the dye for only 30 minutes.

But for chemically treated hair, the processing time is longer since the hair now has artificial pigments. Leave the dye for 35-45 minutes for optimal results.

3. Hair thickness

The dyeing process only takes 30 minutes if you have thin strands. For medium strands, the process may take 30 to 40 minutes, whereas, for thick hair strands, it may take up to 45 minutes.

4. Hair porosity 

Porosity is the hair’s capacity to absorb moisture. Now, how do you know your hair’s porosity? 

Easy! 

Dipping a few hair strands in a cup of water can instantly reveal your hair's porosity.

Hair is highly porous if it sinks in less time than five minutes. If your hair is still floating after five minutes, it has a low porosity, which makes it more dye-resistant. 

Extreme porous hair needs less time compared to low porous hair. 

Semi-permanent hair dyes

Now, let’s go to semi-permanent dyes. 

Semi-permanent dyes do not have ammonia and peroxide, unlike permanent dyes. The new color merely sits on top of the cuticle and does not penetrate thoroughly, reducing the processing time. 

So how long should you leave semi-permanent dyes on the hair? 

Well, it varies depending on the brand. 

Some recommend 15 minutes, while others recommend up to 45 minutes. Hence, always check the directions indicated before you begin dyeing your hair. 

For your reference, here are some brands with their corresponding processing time: 

  1. Arctic Fox - 30 minutes
  2. L’Oréal Colorista - 15 to 30 minutes
  3. Manic Panic - 5 to 10 minutes
  4. Wella Color Touch: 10 to 20 minutes
  5. Splat Hair Dye: 45 to 60  minutes

CHECK OUT: Manic Panic vs Arctic Fox


What happens if you don't leave hair dye in long enough?

What happens if you don't leave hair dye in long enough

We already know what happens if we leave hair dyes longer than advised. But what about leaving it for a shorter time? If you leave hair dye on for less time, will it be lighter? Let’s find out!

Leaving permanent dyes for less than 30-45 minutes results in an uneven coloring job. The ammonia won't fully penetrate the hair fiber, thereby producing a faint color that quickly fades

Another possible result is your hair color may stay the same. 

And not just that, your hair may break too! 

Similarly, leaving semi-permanent dye for a shorter time may likewise result in color fading or a lighter color. It is also possible that the dye won’t penetrate the hair, so the color remains the same after application.

So always follow the recommended exposure time. Otherwise, you’re in for a big mistake. 


How long to leave hair dye in before rinsing

For semi-permanent dyes, simply follow the instructions indicated in the manufacturing box.

But for permanent ones, remember these two factors: your chosen color and the reason for the coloring job.

If you opt for a light color, wait 45 minutes before rinsing. Lighter dyes have weaker pigments, so it requires a longer waiting period. 

But if you’re dyeing your hair with a darker shade, leave it only for 30 minutes. Dark-colored dyes have stronger pigments that easily deposit in the hair. 

Now, let’s go to the second one — the reason why you’re dyeing your tresses.

If you’re touching up the roots, leave it for 30 minutes. However, if it’s your first time coloring your tresses or you’re touching up your color, wait for 45 minutes before rinsing it off. 

Also, remember the 4 other factors mentioned earlier — hair thickness, hair porosity, hair condition, and hair color. 


Does leaving the dye in longer make it darker?

The answer depends on whether you use a permanent or semi-permanent hair dye. 

Leaving a semi-permanent hair dye longer than the recommended time makes the hair darker since it doesn’t have a developer or lightening agent.

But it’s a different story with permanent dyes. 

The oxidation process in permanent dyes alters the hair color. Leaving it longer than advised will not darken the color and only harm the hair. 


What happens if you leave hair dye in for an hour?

What happens if you leave hair dye in for an hour

Let’s not beat around the bush — leaving hair dyes for an hour won’t do any good. And yes, this applies to both permanent and semi-permanent colors.

Color longevity 

Saturating your tresses with color pigments reduces color longevity. Leaving semi-permanent dyes in the hair for an hour results in an overabundance of color. The excess color comes off upon washing, giving you that faded hue.

Leaving permanent dyes on for an hour won’t extend color longevity too.

Permanent dyes penetrate the innermost layer of the hair through the cuticles. However, the hair can only retain a certain amount of pigment.

Once it reaches its maximum threshold, the coloring process is done. 

Scalp irritation

Another possible outcome is scalp irritation. Permanent dyes have ammonia and developer, which may damage the scalp. Some semi-permanent dyes also contain paraphenylenediamine (PPD), which could likewise harm the scalp. 

Hair damage 

Permanent hair dyes have chemicals that penetrate the hair within 45 minutes. But if you exceed this time frame, your hair will now absorb chemical residue that inhibits moisture and nutrients. So as a result, the hair weakens and dries out. 

It becomes frizzy, and split ends may appear. 

For semi-permanent dyes, hair damage is the least of your concern. This type of dye only covers the hair surface, making it less harmful even when left in for more than 30 minutes.

Uneven color 

You may experience an uneven color when you leave permanent dyes in for an hour. 

If your hair is highly porous, the color may appear darker at the ends and lighter at the roots.

CHECK OUT: How to fix over toned hair


What happens if you leave hair dye in for 2 hours?

We’ve already learned that leaving hair dye in for an hour is a huge blunder, especially if you use permanent ones. What more if you leave it in for 2 hours? 

So there goes the answer to that question.   


What happens if you leave hair dye in overnight?

You should never leave hair dyes on your hair overnight, regardless if it’s permanent or semi-permanent! 

Hair dyes only work within a time limit of  30 to 45 minutes. Hence, leaving it overnight is useless and will only result in a major disaster — hair becomes brittle and damaged. 

The color won’t darken either for permanent dyes. Rather, it dries out and sticks to the hair, making rinsing a challenge. 

So my advice — always stick with the recommended time frame! 


The final verdict: Can hair color be left on too long?

Yes, but it’s never a good idea, especially for permanent dyes. 

Aside from drying out the hair, prolonged hair dyeing may cause allergic scalp reactions. 

Chances of hair breakage increase too! The hair may become brittle once exposed to harsh chemicals for a longer period of time.

However, you may go beyond the recommended time frame for semi-permanent ones if you’re aiming for a darker hue. 

Nevertheless, be careful and look out for any adverse reaction.  

At the end of the day, it’s better to be safe than sorry. 

Last Updated: November 22, 2022

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