Going on a vacation? Colour your hair cherry cola red. Feeling the blues? Go for the rich brunette hue. But you can be an inch away from disaster if you don’t get the timing right. Box dye, or salon service, it’s all about knowing how long you should leave hair colour on.
To avoid ending up with brittle strands and an irritated scalp, here are the timings and tips we’ve provided with the help of experts at Pink Lime Salon.
How Long Should You Leave Hair Colour On?
For most of the hair dyes, the ideal time is between 20 to 45 minutes. Here is a cheat sheet based on the type of hair colour.
| Type of Hair Colour | Processing Time | Details |
| Permanent Hair Dye | 30–45 minutes | For colour that stays longer and gives grey coverage. Lifts and deposits colour. |
| Semi-Permanent Hair Dye | 20–30 minutes | Great for showing tones and adding subtle colour. No ammonia or developer |
| Demi-Permanent Hair Dye | 20–40 minutes | These are for blending greys and contain no ammonia. Lasts longer than semi-permanent dyes. |
| Temporary Hair Colour | 5–15 minutes | Sits on top of the hair shaft. You can wash it out in 1 or 2 shampoos. |
| Bleach (Lightener) | 15–45 minutes | Lifts natural pigment. The timing varied depending on your hair and developer strength. |
So, how long should you leave hair dye in? The chart above works, but a few factors affect the timing.
The 6 Factors That Control Your Colour Clock
The instructions on the dye box are important, but they don’t know your hair personally. Here’s what else affects your timing and colour.
- Hair Texture: Fine hair absorbs and processes colour much faster. Coarse hair takes longer to absorb. The latter has tightly packed cuticles, unlike thin hair.
- Hair Porosity: If your hair is porous, you have to be very careful when colouring your hair. The colour will sit on your hair much faster and look darker than expected.
- Starting Shade: Lifting colour from dark hair takes more time and effort than colouring lighter hair. Expect a longer processing time if you’re going several shades lighter.
- The Last Colour: If you have virgin hair, meaning you never dyed your hair, it is most likely to take less time. When you have old dye sitting on your hair, the pigment blocks the new colour at first. You’ll then need to use a colour remover or will need to leave the colour longer.
- Developer Strength: The volume of your developers dictates the speed. A 10-volume is for gentle, slow processing. A 30- or 40-volume is for good lift.
- Environmental Heat: Colouring hair in a warm room speeds up the process. Or, if you are using a plastic cap, it will trap body heat from your scalp, accelerating the colouring.
Let’s say you’re thinking about how long to leave semi permanent dye on hair? The box suggests 20-30 minutes. But if your hair is pre-lightened and porous, that colour might develop fully in just 15 minutes! This is why a strand test is always your best friend.
What Actually Happens if You Leave Dye on Too Long?
These are the things you might experience if you leave the hair colour on for a long time:
For Permanent & Demi-Permanent Dyes
If you’re touching up roots, you may be asking how long to leave permanent hair dye on roots. Leaving permanent dyes any more than 45 minutes will make your hair look like straws.
These dyes work with the help of a chemical reaction. That reaction opens the hair cuticle to deposit the colour. After the reaction stops, you don’t get any more colour, just more damage.
For Bleach / Lightener (The Most Dangerous Category)
How long to leave bleach on hair? Leaving bleach on for too long is the #1 cause of major hair disasters. Bleach doesn’t stop working. It continues to dissolve the protein (keratin) in your hair until it’s rinsed out.
It can melt your hair and make your strands feel gummy.
Bleach can also cause scalp burns if left for too long. That’s why it’s always best to colour your hair from a professional salon.
For Semi-Permanent Dyes (The Exception)
This is the one category where the rules are a bit different. Semi-permanent dyes are “direct deposit” colours. There is no ammonia or peroxide, and it simply stains the outside of the hair shaft. The only problem is that your hair dries out if you leave semi-permanent dyes for too long.
Final Thoughts
Getting the timing right can give you that “wow” effect. But, knowing how long to leave hair colour on helps you avoid spaghetti-like, dried and damaged hair.
But if you’re staring at the box and would rather be sipping a coffee while someone else works the magic, we totally get it. Trust the professionals. At Pink Lime Salon, our stylists will custom-mix your shade and time it to perfection!
