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What Happens If You Leave Hair Dye in Too Long?

“What happens if you leave a hair dye in too long?” is a question we get often. In this guide, we’ll show you various aspects of hair dye, including the hair dye best practices and the best duration to leave in your hair dye.

What Happens If You Leave Hair Dye in Too Long?

Image titled What Happens If You Leave Hair Dye on Too Long featuring a woman in a salon chair smiling getting highlights

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If you leave hair dye for too long, the chances are that the dye might damage your hair. However, this depends on various factors including, the hair thickness and the dye type.

You should understand all these factors and other aspects of hair dyeing before you indulge in DIY hair dyeing practice. In this guide, you will learn:

  • How hair dye works
  • Harmful ingredients in hair dye
  • How long you should leave hair dye on
  • Things to avoid when coloring your hair
  • Frequently Asked Questions on hair dyes
  • What happens when you leave hair dye for too long
  • What you should do if you leave your hair dye for too long

Read on to see what happens if you leave hair dye in too long and other questions surrounding hair dyeing.

Understanding How Hair Dye Works

How hair dye works depends on whether you use a non-permanent or a permanent hair dye. 

Non-Permanent Hair Dye

Non-permanent (also called semi-permanent) hair dye coats the hair strands to give them a new color without penetrating the cuticle to change the hair’s molecular composition.

Their failure to penetrate the cuticle is contributed by the lack of chemicals like ammonia and peroxide, which are responsible for penetrating the cuticle and changing the natural pigmentation of the hair strand. 

Permanent Hair Dye

Permanent hair dyes work by penetrating the hair cuticle and bonding with the hair by changing the molecular composition in the hair cortex. While you can remove non-permanent hair colors, permanent dyes do not fade off.

However, that does not mean that you can’t change them. Essentially, you can change the first permanent coating up to three times using darker or lighter hues.

Harmful Ingredients in Hair Dye

Woman mixing hair color in a bowl for a piece on what happens if you leave hair dye in too long

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Not all dyes are safe for your hair. Some dye products from fake manufacturers may contain harmful chemicals that harm your hair more than good.

Familiarizing yourself with these toxic ingredients can help you pick products whose elements would add value to your hair. Examples of these harmful ingredients include:


Ammonia is commonly used in permanent dyes to allow the dye to penetrate through the hair cuticle into the cortex. Though ideal for the penetration of the hair cuticle, its excessive use can cause hair dryness or damage it. Additionally, too much exposure to ammonia can irritate the throat and cause respiratory issues.

Para-Phenylenediamine (PPD)

Para-Phenylenediamine (PPD) can be found in permanent and semi-permanent dyes. While the product is effective, it can cause severe side effects, especially to people with scalp allergies.

It triggers allergic reactions and increases skin sensitivity. Long-term exposure to this chemical can cause cardiac health issues and respiratory problems.

Titanium Dioxide 

Titanium dioxide is a common ingredient in some hair dyes, but excessive exposure causes carcinogenic effects. It’s advisable to avoid this chemical product to keep safe from the potential carcinogenic effects.


Resorcinol triggers allergic reactions, so it’s unsuitable for people with high skin sensitivity. Besides, the chemical is highly combustible and can cause abdominal issues when you accidentally inhale it.  

How Long You Should Leave Hair Dye In

Woman dyeing her hair at home while looking in a mirror

Simona Pilolla 2/Shutterstock

Many hair dyes come with usage instructions and mention how long you should leave hair dye on. However, most dyes work in 30 to 45 minutes, so you should only leave them on your hair for 30 to 45 minutes.

It’s worth noting that this timing may not work for everyone. For instance, some people may require a longer period if the hair is thick. Here are the main factors determining how long you can leave hair dye on.

Hair Color

Every dye comes with some images showing the expected dyeing results. If your hair color is similar to the desired results, then the process may take a shorter period. For instance, if your hair is brown and you are using a light brown dye, your process will be faster than if your current hair is black.

Hair Thickness

Hair strands come in three main thickness categories: thin, medium, and thick. Thin hair strands are the lightest and take the least time to change color. If your hair has light strands, the dyeing process should take the least amount of time, i.e., 30 minutes, to avoid damaging it.

Medium hair has a medium thickness, and it’s the most common. It can take 30 to 40 minutes to change color when dyeing.

The last hair strands category is thick, which takes the most time during the dyeing process. You might also need more dye products for excellent results if you have thick hair.

Hair Porosity

Hair porosity refers to the ability of hair to absorb moisture for a specified period. Hair porosity can range from high to low. You can quickly know the porosity of your hair by dipping a few strands of your hair in a cup of water.

If the hair sinks in less than five minutes, then your hair is highly porous. If your hair still floats after five minutes, the porosity is low, which means that the hair will be a bit resistant to dyeing.

So, highly porous hair requires the least time to dye, but you may need an average of 45 minutes if your hair does not readily absorb moisture.

What Happens If You Leave Hair Dye in Too Long?

Distressed woman panicking because she left hair dye in too long and her hair got dry

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Multiple possibilities can unfold when you leave hair dye for too long. 

Semi-Permanent Dye

Semi-permanent dye does not contain strong chemicals, so there’s nothing much to worry about when you get busy and forget to rinse in time. However, leaving the dye on for an extended period can bring a darker shade than your expectations.

Permanent Dye

Permanent dye contains strong chemicals, so you can easily land in trouble for forgetting to rinse in time. When the dye remains on hair for long, the dye absorbs moisture in the hair follicles, leaving your hair dry. Excessive hair dryness can make the hair break, especially if the strands are thin.

What Should You Do If You Leave Your Hair Dye in Too Long?

There are valuable solutions to consider when you accidentally dye your hair too long. Here are some of them:

  • Avoid heat styling solutions such as flat iron to avoid causing further damage to the hair strands
  • Apply hair conditioner to keep your hair moisturized
  • Decrease the hair washing frequency to prevent hair loss
  • Seek professional help if you find it hard to restore your hair

Things to Consider

Woman showing us how long to leave hair dye in

Simona Pilolla 2/Shutterstock

You can dye your hair if you don’t get time to visit a salon. The process is easy, but there are mistakes that you should avoid to improve safety and get the best results. Here are some of them:

Choosing the Dye

The success of your hair dyeing procedure starts with the hair color you choose. Do you want a permanent or semi-permanent hair dye? And how many boxes will you need to get your desired results?

Better yet, which dye shade do you need? It’s essential to understand the different dye options to choose the best one for your hair color and texture.

  • Washing Your HairWashing your hair immediately before dyeing may affect your scalp, especially if you have sensitive skin. Unwashed hair creates a barrier to your scalp, which means you don’t quickly develop irritation during the process.
  • The Patch Test – A patch test is essential if it’s your first time applying a particular dye. You should first test the dye with only a patch of your hair. If all goes well without any irritation, you can go ahead and dye the rest of the hair.
  • Applying the Dye – The dyeing process requires a systematic approach to ensure the results are even. If possible, you should divide the hair into four main parts to dye one section after the other.
  • Timing – It’s essential to follow the manufacturer’s instructions regarding the processing time. As a rule of thumb, you should wait for 30 to 45 minutes before you rinse.

Frequently Asked Questions

Here are four commonly asked questions to put your mind at ease if this is your first time considering hair dyeing:

Should I visit a professional or color the hair myself?

You can consult a licensed professional on the best hair dye for your color. The hair expert can guide you if you need a DIY application or help with the dye application.

Can dye damage my hair?

No, the dye does not damage your hair follicles. However, you can improve dyeing safety by avoiding dyes with harmful chemicals and working with a professional.

Can hair dye cover my gray hair?

Yes, dyeing is an excellent solution to gray hair. A permanent dye solution is best if you have more than 60% gray hair.

After how long should I wash my hair after dyeing?

Wait for a minimum of 24 hours before you apply shampoo to top your freshly dyed hair. Also, limit hair washing to a maximum of three times per week if the dye color is intense.

So, What Happens If You Leave Hair Dye in Too Long?

Leaving hair dye for too long may damage your hair. You should only leave most dyes in for 30 to 45 minutes. In case you leave it for too long, don’t fret! Follow the tips above to avoid further damage.

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