How Long to Leave Hair Dye in Your Hair

How Long to Leave Hair Dye in Your Hair

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Are you going to try hair dyeing at home for the first time?

Don’t worry. Dyeing your locks should be easy as long as you know the basics.

Before you get that perfect at-home box dye, make sure you’ve already thought about the color you want, the type of dye you’re using, and how long to leave hair dye in.

Woman in salon chair having her hair dyed

Don’t make the mistake of not being prepared. Remember that permanent dye contains chemicals that can ruin your locks if you don’t use it properly.

That’s why we’re here to help you understand how important it is to leave the dye in for the right amount of time so that it works well and you can avoid over or under-processing your hair color.

How Long Should Hair Dye Stay in Before Washing?

Many hair dye products come with instructions telling you how long to leave hair dye on your hair before you rinse it. Most say that dye needs a minimum of 30 to 45 minutes to process.

This is a good base, but the truth is there is no exact answer to how long to let the dye sit in the hair because the timing may have a different effect for everyone.

Remember, everybody’s hair is different. And how long to let dye sit in hair depends on various factors, including your hair type, condition, and the hair dye you’re using.

Factors That Affect How Long to Keep Hair Color In

Here are the things you should know about before coloring your hair. When you better understand these factors, you’ll know the best timing for your hair dye and get the best color results.

Type of Hair Dye

Hair dyes are classified according to how they work, and these types have different processing times.

Types of Hair Dye

  • Temporary
  • Semi-permanent
  • Demi-permanent
  • Permanent

This article won’t talk much about temporary hair dyes because these products are only meant to stay on your hair as long as you need them and are usually washed out when you shampoo..

Permanent Hair Dyes

This type of dye is classified as permanent because it’s resistant to shampoo washes and other styling or hair processes. The reason is that the permanent hair dye color is inside the hair cortex.

Most permanent dyes use ammonia because it serves as an alkaline medium that lifts the hair cuticles. Ammonia can only do its work when activated using an oxidizing agent, which we commonly know as a developer.

Ammonia-free hair dye still lifts the cuticles but through an alternative alkaline ingredient to have the same lifting effect.

The entire cuticle lifting process typically takes around 15 minutes, 20 if the hair is harder to penetrate (we’ll talk about that below.)

Once the cuticle has been lifted, the dye molecules can enter the hair shaft. The developer oxidizes the dye molecules inside the hair cortex, causing color formation.

For the color to fully develop, it takes approximately 15 to 20 more minutes.

That said, how long to leave permanent hair dye in is at least 30 minutes or longer, depending on your hair type.

Demi-Permanent Dyes

Demi-permanent hair color, like permanent color, is also based on oxidation dyes. Their difference is the alkaline medium used.

The former usually uses monoethanolamine with low lifting power. Because of this, demi-permanent hair dye should be left in for the same amount of time as permanent hair color.

Semi-Permanent Dyes

Semi-permanent hair dyes are also called direct dyes because they don’t require a developer. Instead, they have color molecules that directly attach to the hair cuticles.

Some dye molecules can penetrate the hair shaft a bit, making the semi-permanent dye a bit more resistant to fade than temporary dyes. 

But, overall, semi-permanent hair dye doesn’t deposit hair into the cuticle but instead coats them with color.

Because there’s no oxidation process involved in using semi-permanent dyes, the recommended amount of time is 20 to 30 minutes.

But some people who want brighter or darker hair color need to leave hair dye in for longer. And it’s okay to leave it in for longer because semi-permanent hair dye won’t dry out your hair.

Hair Porosity

Another factor to consider when deciding how long to leave hair dye in is your hair porosity. Different levels of porosity absorb dye at different speeds.

Let’s quickly talk about hair porosity levels to understand how they differ.

New York Society of Cosmetic Chemists (NYSCC) defines hair porosity as the strand’s ability to absorb and retain water and products based on the integrity of the hair cuticle.

The cuticle is the hair strand’s outermost layer, which is the hair’s coating or protection. And the cells in the cuticle are arranged like roof shingles.

Your hair porosity depends on the condition of the cuticles and how these roof shingles look on your hair strands.

Porosity LevelCuticle Condition
Low porosityThe cuticle cells lay flat and are tightly packed, so there are very few gaps in between for the dye molecules to enter.
Normal porosityThe cuticles are slightly raised and are not too close to each other, leaving enough space for the product to go through.
High porosityThe cuticles are lifted and wider apart so the dye molecules can easily penetrate the hair shaft.

Low-porosity hair is harder to dye because of its closed cuticles. The alkaline medium will need more time to lift the cuticles than healthy hair with normal porosity. 

It’s also harder for semi-permanent dyes to attach the molecules to the smooth strands.

The easiest hair to dye is highly porous hair because it absorbs dye molecules the fastest. However, this hair condition is also most likely to suffer from over-processing.

Knowing your hair porosity will help you understand how long you need to leave your hair dye in for the best color outcome.

You can try easy porosity tests at home like these to know your hair porosity level.

Hair Thickness

Hair can also be classified according to the strand’s thickness, which can impact the processing time of hair dyes.

Hair Types According to Diameter

  • Fine
  • Medium
  • Coarse

To see what your hair type is, look closely at a strang of your hair.

  • If you can barely see the strand, you have fine hair.
  • If the strand looks and feels thick, you have coarse hair.
  • If it’s somewhere in between, you have medium hair.

Dyeing fine hair is faster, so 30 minutes is ample time. However, coarse hair may need up to 45 minutes because dye takes longer to permeate thick strands. 

How Long to Leave Hair Dye in Your Hair

In light of all the factors we’ve discussed, you probably understand by now that there’s no one answer to how long to leave hair dye in your hair before you rinse it.

The best way to find the perfect time is to do a strand test first. The results of this test will determine how long you should let the dye sit on your hair.

Strand Test

  • To do a strand test, grab a thin section of hair from the back of your head (not easily noticeable), and follow the instructions on the dye to color it.
  • After half an hour, check on that section and see if you’re happy with the color.
  • If not, leave it in for longer, checking in every 5 minutes until you’ve reached the maximum time of 45 minutes.
  • For the best, most accurate results, recheck the strand 24 hours later. The color will have settled, and you’ll have the best gauge for how it will look.

Note the time it took for the dye to achieve the color you want, and use that processing time when you color the rest of your hair.

Alongside the strand test, we also have hair dye timing tips for other hair conditions.

Dyeing Virgin Hair

Woman looking in the mirror dying her hair at home

If your hair hasn’t gone through any chemical process before, it’s considered virgin hair. While DIY hair coloring may seem intimidating initially, it’s possible to do it without ruining your locks.

Generally speaking, virgin hair is easier to dye because it has healthier hair fibers that react quickly to hair products.

Because of that, 30 minutes is enough for the strands to be fully colored. Don’t leave it in much longer, as you don’t want to over-process your hair.

Changing the Color of Pre-Colored Locks

If you are tired of your previous color, you might want to dye your hair again. That’s okay, as long as at least two weeks have passed since your last color (the longer, the better).

If the new shade you’re going for is similar to what you already have, you won’t have to wait extra time for the color to process.

For example, if your hair is previously dyed brown, changing it to light brown or hazelnut brown won’t take as long as making it red.

A drastic color change may take 45 minutes or more because the previous dye pigments may interfere with the new color molecules.

Covering Grays

If you aim to cover white or gray hair, the recommended application is to dye the gray part before the rest of your locks because they need a maximum exposure time of 45 minutes.

They need longer dye time because gray hair is more resistant to color, as it is coarser or thicker in structure. Because of that, the dye molecules will have more difficulty permeating it.

Coloring Your Roots

The next type of dye job is root re-touching. If you don’t have gray hair, the application of hair dye on your roots may differ. The answer to how long to leave hair dye on roots will also be different.

Apply the dye on your roots first if you’re using a shade darker than your present color.

However, we recommend coloring your roots last if it’s a lighter shade. The reason is that your roots are healthier than the lower part of your locks. That and the heat from your scalp will help make the dyeing process faster.

It means that your roots may not need 30 minutes to color (if they aren’t gray).

What Happens If You Leave Hair Dye in Too Long?

Now that you know how long you should leave your dye in, depending on your hair type and the dye job you need. The next question is, inevitably, what happens when you leave the dye on too long?

Does hair dye get lighter the longer you leave it on? Or does it get darker?

If you’re using a permanent dye, the dye will stop developing after a maximum time of 50 minutes, so leaving it longer won’t impact the color.

What it can do is make your hair dry.

The ammonia and peroxide content of hair dye and other potentially harmful ingredients can damage your hair if left on too long.

To be precise, the cuticles will stay lifted when you leave the dye in longer than recommended. As a result, moisture and protein from the hair shaft will be lost, making the hair dry and brittle.

That said, don’t leave the product in for longer than 45 minutes.

As for semi-permanent dyes, the color will get darker the longer you leave it, but never lighter because direct dyes can’t lift pigments.

What Happens If You Don’t Leave the Hair Dye Long Enough?

Not giving the hair dye ample time to process would be a waste of the product and can result in an uneven or underdeveloped color that won’t last.

And you wouldn’t want to waste your product and your time on a color you don’t absolutely love.

So, as a rule of thumb, remember that permanent and demi-permanent dyes need the first 15 to 20 minutes to lift your cuticles, so there will be no color change if the product is left in the hair for less time than that.

Frequently Asked Questions

How Long Does It Take to Dye Your Hair?

The overall hair dye process can take anywhere from 1 to 2 hours. This includes:

  • Preparation
  • Application
  • Processing
  • Rinsing
  • Drying and styling

The time may also depend on the length and density of your hair. The thicker your hair is, the longer it will take to dye.

Should I Shampoo After Hair Dye?

No, you shouldn’t shampoo your hair right after you dye it. It’s best to wait at least 48 hours to wash your hair to allow the dye molecules to settle in your hair strands fully.

Will Leaving Hair Dye for a Shorter Time Make It Lighter?

Leaving the dye in for a shorter time will not make the color lighter. If you want a lighter color, we suggest diluting the dye (works best with semi-permanent) with a conditioner or opting for a lighter dye.

How Long Should You Leave Hair Dye In?

When you color your hair, how long to leave hair dye in before rinsing depends on different factors.

close up of hair dye being applied to roots by hair dresser

You have to consider whether you’re using a permanent or semi-permanent dye. Your hair type is also a factor because some hair structures are more resistant to hair dyes.

To summarize, you should leave hair dye in your hair for a minimum of 30 minutes and a maximum of 45. Avoid leaving the hair dye in too long because this may cause your hair to become dry and brittle.

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