What Happens If You Leave Hair Dye In Longer Than Recommended?

Coloring hair at home is a good way to go if you’re on a budget. But bear in mind that the ingredients in hair dye can be potentially damaging to your hair if not used correctly. This article will explore what happens if you leave hair dye in longer than recommended.

Can I Leave Hair Dye In Longer Than Recommended

Leaving hair dye in hair for longer than recommended can will cause the dye to absorb the moisture in the hair follicles, leaving your hair feeling dry and brittle. 30 minutes is usually long enough for the chemicals in permanent hair dye to develop and permeate the hair.  

How Long Should You Leave Hair Dye In?

Most hair dyes should be left in the hair for at least 30 minutes, and no longer than 45 minutes.

The hair dye requires 30 minutes for the ingredients, ammonia, and peroxide to work into the hair cuticle to change the hair’s natural pigmentation.

The final 15 minutes allow the dye to fully develop and permeate the hair.

Hair dye should not be rinsed off earlier than 20-30 minutes.

To do so would be a waste of the product and you end up with a color different from what you’d expected. It could also result in uneven color coverage throughout your hair.

Conversely, if you exceed the recommended maximum time of 45 minutes, you risk damaging the hair, causing it to become dry and susceptible to breakage.

You can also end up with a color that is much darker than you had expected.

What Happens If You Leave Hair Dye In Longer Than Recommended?

Leaving Hair Dye In Longer Than Recommended

Hair dye contains chemicals that will dry out your hair if left on too long. This is because hair dye draws out the moisture from your hair follicles and as a result, can cause damage to your hair.

It is always best practice to follow the guidelines that the manufacturer has put on the box.

Also, leaving the dye in longer won’t necessarily result in the color being darker or lasting longer. What you will be at risk of is dry damaged hair.

You should also be careful with mixing hair dye with conditioner. Although conditioner will help soften your hair and make you think you can leave it in for longer, it can in fact cause an uneven color.

This goes for diluting hair dye in general.

Also Read: How To Bleach And Dye Hair In The Same Day

Does Leaving Hair Dye In Longer Make It Darker?

This really depends on whether you use permanent or semi-permanent hair dye.

A semi-permanent hair dye will cause your hair to become darker the longer you leave it in. this is because it does not contain developer or a lightening agent.

When you dye your hair with permanent dye, it is the oxidation process that changes hair color.

Leaving the dye on longer than recommended will not result in a deeper color but, at the risk of being repetitive, it will damage the hair.

Let’s look at some examples:

Leaving Black Hair Dye In Longer than recommended

Leaving black hair dye on longer won’t make any difference to the color result. It will just dry out your hair.

Leaving Red Hair dye in Longer than recommended

Red can be tricky. The color doesn’t always come out well which is why a trip to a professional colorist might be in order if you want to go red.

Depending on what your natural hair color is, if you leave the hair dye in longer, it might make it darker.

If that is the case, then it might be a good idea to apply it to your ends where it’s lightest first and then go for those areas which are naturally darker closer to your roots.

The opposite can happen though, where the lighter parts of your hair take well to the red and do so quickly.

Leaving Blond hair dye in Longer than recommended

Leaving a permanent blond hair dye in for longer than the recommended time is really a situation you want to avoid.

However, most box dyes are designed to deactivate after about 45 minutes. Even if you left the dye for more than an hour, you’d still have hair on your head.

But it can be quite detrimental to the hair. If the product contains bleach, it can cause significant damage to the ends of the hair.

Most stylists agree that bleaching your hair, especially if your aim is to go from dark to very light, is something that’s best left in the hands of professionals.

Coloring a Dark dye over bleached hair

Trying to fix the problem yourself, could make it even worse.

When you apply color to hair that you have lightened or bleached, that hair is more porous which means it will be harder to retain moisture.

The possible outcomes you may encounter here are that the hair will be darker on the tips and lighter at the roots.

The other possibility is that the hair can turn murky green-blue in color. The hair needs the underlying tones added back in before you can experiment with darker colors.

This is an exacting science and one that is perhaps best left up to an expert colorist.

Check out this article we wrote on how to use purple hair color on dark hair without bleach.

3 reasons to avoid leaving hair dye in for longer

hair dye can ruin fine hair

There are three types of hair thickness: fine, medium, and thick.

Fine hair is more at risk of over-processing and is more susceptible to damage.

When dyeing fine hair, always be aware of how fast the color is developing as you may need to rinse it off earlier.

high porosity hair is more at risk

This is your hair’s ability to absorb moisture. If your hair has high porosity, it means it will be able to accept more of the hair dye.

This will affect how much damage is caused if the hair dye is left in longer than recommended.

Hair with a higher porosity absorbs dye well so it may not need as much time. You also need to keep a close eye on the color as it develops.

High porosity hair can be more at risk of damage.

Also Read: Does Hair Dye Expire? (Everything You Need To Know)

permanent hair dye is worse than semi-permanent dye

Semi-permanent dyes don’t have ingredients like peroxide and ammonia in them, so they won’t cause too much damage.

To re-iterate the information above, they only deposit color on the external layer of the hair strands so there is no actual bonding with the hair.

So while it is not advised to leave it on longer than the recommended time, if you do, there is no irreversible damage.

Permanent hair dye is a different ball game. These dyes have strong and potentially hazardous chemicals.

They absorb up the cuticle of your hair shaft to let the pigments get to work.

Leaving permanent hair dye in longer than recommended will possibly sacrifice the luster and strength of your precious locks.

How Does Hair Dye Work?

Non-permanent hair dye works by coating each strand of hair with color.

The color is deposited on the outer layer of the hair strands so there is no change to the internal molecular structure.

Alternatively, when using permanent hair dye, each cuticle of the hair is penetrated, the dye then enters the hair cortex and bonds with the hair.

Long-lasting non-permanent hair color can be shampooed out eventually however permanent color, as the name would suggest, permanently colors the hair.

On average, most hair dyes should be left in the hair for a minimum of 30 minutes, and no longer than 45 minutes. However, it is important to follow the instructions on the packaging as well as dispose of hair dye the right way.

The hair dye needs 30 minutes for the ammonia and peroxide to get into the hair cuticle to change the natural pigment of the hair.

The final 15 minutes are for the dye to fully develop and permeate the hair.

Harmful Ingredients In Hair Dye

Permanent hair dyes can contain some very hazardous ingredients. In fact, some even believe that hair dye has the ability to kill lice.

There are many ingredients used in the manufacturing of hair coloring products and they actually differ between countries.

Each country varies as to which ingredients are deemed safe enough for use.

To avoid toxic chemicals in hair dyes it is important for the consumer to know a little bit about which chemicals are the harmful ones.

According to Holland and Barratt, the main chemicals to be aware of are p-Phenylenediamine, ammonia, hydrogen peroxide, and lead acetate.

Semi-permanent dyes do not contain these potentially harmful elements. They don’t open the shaft of the hair so the change is only on the surface and not on a molecular level.

However, remember that you are still applying a certain amount of chemicals to your hair which can have a drying effect.

Note: It is important to do a patch test first before you apply any coloring product on the hair to check for allergic reactions.

Factors Which Affect Time Taken For The Dye To Work

How Much Gray Is In Your Hair

When covering gray hair, the dye should be left on for 45 minutes. You will also need to use permanent dye because semi-permanent ones won’t have much effect.

The Thickness Of Your Hair

Fine hair can be quite prone to damage.

As previously mentioned, when dyeing fine hair, always keep an eye out on the rate at which the color is developing as you may need to rinse it off earlier.

Medium hair usually gets good results from leaving hair dye on for 45 minutes.

Thick hair can be the hardest type to treat. Strands are thicker, and there’s often a lot of it. Thick hair usually needs a little more time when being dyed, and also needs more product.

Your Hair’s Porosity

Hair that is highly porous will be able to accept more of the hair dye.

You’ll need to keep a close eye on the development of color on highly porous hair as it can be left more open to damage.

Low-porosity hair can be more resistant to hair dyes, and you’ll need to give it a full 45 minutes when dyeing.

Also Read: The 10 Best Orange Hair Dyes

How Long For Covering Gray Roots?

Depending on the brand of dye you are using, apply to the roots for 30 minutes or longer.

If this is the first time to color your hair, then finish applying all of the product throughout the hair after the roots are done.

If your goal is only to refresh your remaining hair, wait 10 minutes before you need to wash out to apply the remaining color.

Can I Leave Semi-Permanent Dye In My Hair All Night?

The longer you leave semi-permanent hair color in, the darker your hair will get.

However, there is a saturation point when the hair won’t take any more color so leaving the dye in all night is a pointless exercise.

Leaving in semi-permanent hair color too long can result in your becoming over-processed causing split ends, and dry, brittle hair.

What happens if I leave in Permanent Dye All Night?

Leaving permanent hair dye in your hair all night, again, will make little difference to the color outcome. But it will harm your hair and leave it straw-like.

Think about what you are trying to achieve by leaving the dye in for longer. If it is a darker color, then just go ahead and commit to purchasing a product that will achieve darker results.

Also Read: How To Get Hair Dye Out Of Carpet (4 Easy Ways)

Things To Avoid When Coloring Your Hair


woman having her hair colored

1. Not Doing A Patch Test

It’s important to do a patch test prior to coloring your hair each time – even if you have colored your hair before.

2. Expecting The Color To Turn Out Exactly As The Picture On The Box

You should be aware that the swatches of hair you see attached to the shelves at the drugstore are actually white hair that has been dyed. So it is unlikely that your hair will turn out that exact color. Everybody’s hair is different.

3.  Applying The Product Incorrectly

Celebrity hair stylist Chelsea Pickthorn advises caution when applying the dye, especially to hair around the face.

It is the easiest part to see and because it is in contact with products from our face it processes the dye differently and absorbs more color so it can come out darker than the rest of the hair.

4. Bleaching Hair

Professional stylists strongly advise against bleaching hair at home. There are so many ways it can go wrong.

Emily Baum, a New York City-based colorist warns bleaching is ‘the most intense chemical process you can do’. The best thing to do is go to a professional colorist.

5. Trying To Darken Hair Which Has Been Lightened

This can be a risky thing to do as hair that has been lightened is more porous which means it won’t necessarily react to dyes the way uncolored hair would.

It can either overcolor, or turn blue, green, or a murky swamp-like color.

Repairing Damaged Hair After Leaving Hair Dye In Too Long

If you find yourself in a situation where you have left the hair dye on too long, don’t panic. All is not lost- your hair will not fall out! However, you will have to show it some love to nurse it back to health.

Avoid Heat Styling

This means no hairdryer, flat iron or curling iron for at least a month. These tools damage your hair anyway so will add to the damage if used on fragile hair.

Pamper Your Hair

A great solution for nourishing your hair is using coconut oil. Apply it twice a week and leave on all night. Just pop a shower cap on and a towel on your pillow to protect your bedding.

Extra virgin olive oil will also work if you don’t have coconut oil. Warm your chosen oil up (but not too hot!) and then slather it on. In fact, olive oil is also a natural way to remove permanent hair dye if needed.

And don’t worry- leaving nourishing oils on your hair for such a long time won’t cause problems.

Look After Your Hair From The Inside Out

Trying a few of these tips will help you on your journey to repairing hair damage and keeping hair healthy and strong.

Include plenty of protein into your diet (nuts, seeds, quinoa); use a hair product that contains keratin; try to keep stress levels low (perhaps easier said than done!).

Be Gentle

When washing your hair, be gentle. Use a moisturizing shampoo free of sulfates. Your conditioner should also be sulfate-free and good for restoring moisture to damaged damaged hair.

Cut Off The Damage

Worst case scenario, if the hair is very damaged from overprocessing, you may have to have to trim the ends.

Depending on how damaged it is, you may need to have more than an inch taken off, otherwise, it may continue to split up the shaft of the hair.

So, to round it all up, leaving hair dye in longer than the recommended time (especially permanent hair dye) should be avoided at all costs. But if the worst happens, it is possible to turn it around and restore your luscious tresses with a little tender loving care.

Frequently asked questions (FAQ)

What Happens If You Leave Hair Dye In For An Hour

You won’t cause irreversible damage if you leave hair dye in for an hour however you should always follow the instructions on the box. Make sure you rinse out all of the dye.

What Happens If You Leave Hair Dye In For 2 Hours

If you leave hair dye in for 2 hours, you may put your hair at risk of damage. Permanent hair dye will not continue to get darker, it will only dry out your hair.

Does Hair Dye Stop Processing After A Certain Time

Hair dye usually stops processing after 45 minutes so there would be no reason why you should leave the dye in for longer than the recommended amount of time.

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