How Long to Leave Hair Dye In: Semi-Permanent and Permanent

African American female wearing a white t-shirt with light brown dyed hair on naturally black hair.

Timing is everything when it comes to dyeing your hair. The duration you leave the hair color on will determine how vibrant and long-lasting your dye results will be.

This article will explain how long to leave hair dye in your hair, including permanent and semi-permanent hair color, what happens when you don’t get the timing right, and more. Let’s get into it.

Key Takeaways

  • Recommended Time for Hair Dye: For gray hair, leave the permanent dye on for about 45 minutes; for root touch-ups, 45 minutes is typical. Semi-permanent dye generally requires 30 minutes. Adhering to these times ensures the desired color results.
  • Hair Type Considerations: Thick hair and high porosity strands might need longer processing times for the dye to penetrate effectively, while fine or thin hair may require less time to avoid damage. Understanding your hair’s porosity and thickness is crucial for effective dyeing.
  • Importance of Strand Test: Conducting a strand test before a complete application is a good idea, especially for first-timers or when changing to a darker or lighter color. It helps predict the color outcome and assesses how your hair reacts to the dye.
  • Impact of Natural Oils and Hair Condition: Natural oils and the condition of your hair can affect dye uptake. Using clarifying shampoo before dyeing your hair can remove build-up, but avoid washing with hot water right before dyeing to preserve natural oils that protect the scalp.
  • Aftercare and Maintenance: Post-dyeing, use color-safe shampoos and avoid hot water to maintain the new hair color. For those with curly or specifically textured hair, using products designed for your hair type can prolong color and maintain hair health.

How Long to Leave Permanent Hair Dye in Your Hair

Permanent dyes contain chemicals that activate at specific time intervals when applied to the hair. So, you must allow the dye to sit for the specified time to enable the product to do its work.

In this section, we will explain how long permanent hair dye should be left in and why these time recommendations matter.

For Gray Hair

Gray hair is the most resistant to new pigment because of its dry, coarse texture. It lacks sufficient sebum, the natural oil produced by the scalp, and that lengthens the color-depositing process.

So, if you have gray or white hair, be prepared to carve out about 45 minutes to color it with permanent dye. During the first 15 minutes of dyeing gray hair, the dye’s main chemicals, peroxide, and ammonia, penetrate the cuticle layer to lift the hair’s pigment.

In the last 30 minutes, the dye molecules develop and impart new color to the hair strands. This same chemical process can be used for covering gray roots.

Young black female in casual clothes with a dark brown natural hair color on 4A fine hair strands.

For Root Touch Ups

Hair dye processing times for root touch-ups vary depending on your hair type and color. But generally, hair dye should be left in for 45 minutes when focusing on the roots. In this section, we’ll explain a few situations where hair color processing times vary when coloring roots.

Touching Up Gray Roots

If you’re touching up gray or white roots, you should let the color sit on your hair for 45 minutes. Gray hairs have no pigment, so they require the longest color processing times.

For those with stubborn, color-resistant grays, a process called pre-pigmentation can be done within the same 45-minute period. This process involves opening the cuticle layer using ammonia, the dye’s alkaline agent, before applying the developer to the hair.

This process helps the dye penetrate deeper into the hair shaft for vibrant, long-lasting color. Read on to learn how to pre-pigment your gray roots.

What You’ll Need


  1. Dispense half of the hair dye into the bowl, mixing it until it is creamy.
  2. Apply the dye onto your roots using the applicator brush.
  3. Let the dye sit on your hair for 5-10 minutes.
  4. Mix the rest of the dye with the developer (according to the instructions on the dye) until it is smooth.
  5. Apply the mixture to your roots using the applicator brush.
  6. Cover your head with the plastic cap and let the dye sit on your hair for 35 to 40 minutes.
  7. Rinse the dye out with cool water until it runs clear.
  8. Shampoo, condition, and style as usual.

Touching Up Roots with Highlights

You should allow 45 minutes to touch up your roots when you have highlights. Roots require longer processing times than mid-lengths and ends.

This is because your root’s cuticle layers are typically smoother and more closed. Moreover, the dye’s chemicals need more time to deeply penetrate the cuticle layer to inject the new color.

Charming African woman with 4A thick hair dyed by a hair colorist wearing a white t-shirt and jeans.

When touching up your roots, there’s a certain technique you should use to preserve your highlights. Below are easy instructions on how to complete this technique for refreshed roots and flawless highlights.

  1. Mix the dye and developer according to the instructions on the packaging. 
  2. Apply the dye to your roots carefully, ensuring that it doesn’t touch the mid-lengths and ends of your hair.
  3. Let the dye sit for 40 minutes.
  4. Without rinsing out the dye at your roots, dampen the mid-lengths and ends of your hair with water.
  5. Comb the dye downward until it reaches the entire length of your hair.
  6. Let the dye sit for five more minutes.
  7. Wash the dye out of your hair and style as usual.

For Dark Virgin Hair

Dark toned virgin or unprocessed hair requires the shortest processing times because it retains new pigment easier than chemically treated hair. In most cases, the dye should only be left on for 30 minutes. 

For Pre-Colored Hair

Previously colored hair takes longer to process than virgin hair because it already contains synthetic pigment from the existing hair color. For the best results, the dye should be left in for 35-45 minutes.

Beautiful African American woman 4A hair thickness and darker hair wearing color-treated hair.

How Long to Leave Semi-Permanent Hair Dye in Your Hair

Semi-permanent hair dye procedures are generally shorter than permanent hair dye sessions because these treatments work differently.

Unlike permanent hair dyes, semi-permanent dyes do not deeply penetrate the hair cuticle. The color often sits on top of the cuticle layer, making processing times a lot shorter.

In this section, we will discuss how long you should leave in semi-permanent dye in various situations. Semi-permanent hair dye should be left on gray hair for about 30 minutes.

If you have stubborn grays, sit under a hooded dryer for the full 30 minutes. Similarly, root touch-ups and all-over dye jobs require the hair dye to be left in for no more than 30 minutes.

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

Since hair dye procedures are designed to be completed within a specific time period, speeding up the dyeing process will likely give you disappointing results. In this section, we will discuss the consequences of not leaving hair dye in for the specified time.

Could End Up with Unwanted Tones

If you under-process your hair when lightening it, you could end up with brassy, golden, or red tones. On the other hand, if you under-process your hair when darkening it, your results may be dull and lackluster.

Furthermore, rushing through gray hair coloring sessions could make your strands appear transparent vs. vibrant. 

Cute black girl with medium hair thickness and shoulder hair length wearing a curly twist-out hairdo.

Hair Color Will Not Absorb Properly

If permanent hair dye is not left in long enough, the hair shaft will not retain the color. During the last stage of the dyeing process, the chemicals seal the cuticle to lock the color in.

If you rush through this stage, you may experience color bleeding and fading.

What Happens If You Leave Hair Dye on For Too Long?

Over-processing is far more harmful than under-processing it because of the potentially hazardous chemicals that some dyes contain. Read on as we explain what happens when you leave hair dye on for too long.

Could Damage Your Hair

Permanent dyes contain harsh chemicals that are potent enough to break through your strand’s protective layers.

When the inner hair shaft is exposed to chemicals for long durations, the hair becomes vulnerable to structural damage. The result is excessive hair dryness, split ends, and breakage. 

Could End Up with Darker Tones

Over-processing hair can also leave you with unwanted darker tones. This dilemma usually occurs with permanent hair dyes, as they contain ingredients that inject the hair with pigment until they are deactivated, resulting in dark hues.

A young African American woman with high porosity hair caused by overusing box dyes.

Hair Dye Processing Times Vary Based on the Brand

Depending on the brand and type of hair dye you use, the processing time will vary. To ensure you get the best results from your hair dye, always follow the instructions included with the dye. Note that most hair dyes come with detailed instructions, if not, check YouTube to see if you can find a detailed tutorial from a previous user.

Related Articles

Hair dyeing is a calculated procedure that should be done with care. So, before you color your hair, educate yourself on the proper processing times to avoid a botched dye session. We hope this article was helpful to you, and we wish you the best of luck with your hair!

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