If you want to dye your hair, going to a salon will give you the most consistent results. If you’re looking to save some money, though, it’s possible to dye your hair yourself as long as you follow a few rules. One of the most important things to know is how long you should leave your hair dye in.
We’re going to cover how long you should leave it in, different types of dye and the best way to apply it. We’ll also discuss the problems you may run into if you leave it in too long or not long enough.
Getting this right will help you get the hair color you expect and make sure that your hair stays healthy and vibrant.
How long should you leave hair dye in after applying?
As a general rule of thumb, you should leave hair dye in for a maximum of 30 to 45 minutes. There are some exceptions to this depending on the type of dye, as well as the condition of your hair.
Semi-Permanent Dye
Semi-permanent dye is a dye that does not contain bleaching agents, so it won’t penetrate the hair cuticle as permanent dye will. It washes out in 4 – 6 weeks, so is ideal to use if you want to try a color out temporarily. It is also more gentle on your hair. The downside to this type of dye is that it won’t change the color of your hair if your hair is very dark.
You can leave semi-permanent dye on longer than the recommended timeframe to deposit more color. Some people even let it sit overnight. To do this, rub vaseline around the hairline and ears to prevent dye from staining your face. Cover hair with a plastic bag or a cap.
Another way to get semi-permanent dye to release more color without having to leave it on for a long time is to help it process with heat. Heat helps to open the cuticle of hair to let the color molecules penetrate. Put a plastic cap on and warm with a blow-drier for 15 to 20 min.
You can also try applying your semi-permanent color to dry hair. When hair is wet, water clogs the cuticle. Applying hair dye on dry hair will allow more color molecules to attach themselves.
Permanent Dye
Permanent dye contains ammonia and hydrogen peroxide to penetrate the hair cuticle. It will need to be touched up around four weeks as your hair grows out.
Since it changes the structure of your hair, you must leave permanent hair dye in for the right amount of time, which is generally around 30 to 45 minutes.
Hair that is similar in color to the shade you are trying to achieve will not need as much processing time. This is the case if you’re going from a light brown color to a deeper brown, for example.
Fine or thin hair is more delicate and also takes less time to dye. Those with thick or coarse hair will need to leave hair dye on longer or have their hair dying split into multiple sessions.
Another factor to consider when dying your hair and the amount of time to leave hair dye in is the porosity of the strands. Porosity is the ability of your hair to retain and absorb moisture. An easy test to determine whether your hair has high or low porosity is to fill a cup with water and place a few strands of hair in. Highly porous hair will soak up water and sink quickly. Less porous hair will slowly sink to the bottom. Hair with very little porosity will float on top of the water.
Similar to how hair reacts to water, highly porous hair will soak up dye quickly and require less time processing. This type of hair is usually seen in those that have frizzy or damaged hair.
Does it vary by color/brand of dye?
Different brands of semi-permanent hair dye can vary in the amount of time you need to leave them in. Professional variants are stronger, although you would need a cosmetology license to purchase them from beauty supply stores.
Due to the chemical nature of permanent hair dye, it takes 30 to 45 minutes to develop the color and then penetrate your hair. No matter the brand or color, you should not leave permanent hair dye in for longer than 45 min.
While bleach is technically not a dye, it is altering the color of your hair by removing pigment. If you are lightening your hair with bleach, you should be very cautious with the amount of time you leave it in. Hair that has been chemically treated, such as relaxed or straightened hair, should not be bleached at all. Fine hair will only need 10 to 15 minutes, while dark and/or coarse hair will need 30 minutes.
Will you get darker hair if you leave it in longer?
You can get darker hair if you leave hair dye in longer with semi-permanent dyes. For permanent dye, it is not recommended to leave it in longer than the stated time, due to various problems which we will cover below. It would be better to choose a darker shade of hair dye.
What happens if you leave it in too long?
Leaving semi-permanent hair dye in longer than recommended usually isn’t a problem. The main concern is that you will end up with a color that is darker than you expected.
If you leave permanent hair dye in too long, however, multiple problems can occur. Since permanent hair dye changes the structure of your hair with ammonia and hydrogen peroxide, leaving it in too long can make the hair dry, dull, and brittle. The dye also can absorb all the moisture in your hair. Once your hair is too dry, it can break off. Leaving dye in too long causes permanent damage to the hair. Once this happens, there is no way to restore your hair to its former healthy state – the only solution is to cut it off entirely!
Another problem is the risk of an allergic reaction. This can range from a mild rash to extensive swelling, inflammation, nausea, and vomiting. To avoid this, you can perform a patch test before dying your hair. However, leaving hair dye in too long increases the risk of an allergic reaction.
Instead of leaving hair dye in longer than the recommended amount of time, we suggest choosing a darker color or maintaining your color with color depositing conditioners. These help your hair stay healthy while keeping the color vibrant.
What happens if you don’t leave hair dye on long enough?
If you don’t leave hair dye in long enough, there are some additional problems. It is important to get the timing just right!
Washing semi-permanent hair dye out too soon means it won’t get a chance to deposit as much color. The color you do get will fade quickly.
Permanent hair dye contains color and developer to activate the color molecules. It requires the recommended amount of time to develop the dye molecules. If you don’t leave it on long enough, you won’t get the shade the box displays.
What should I do if I’ve left hair dye on too long?
If you left semi-permanent hair dye in too long, wash it out and evaluate the color. If it is too dark, you can wait for it to fade from your hair with time or speed the process up by washing with a clarifying shampoo.
If you’ve left permanent hair dye in too long, apply a deep conditioner to help add moisture to the hair. Avoid further damage to your hair. This means not using heat-styling tools like curling irons and flat irons. Use a microfiber towel to gently blot excess water after washing and then let your hair air dry. Try to reduce the frequency of how often you wash it as well since excessive shampooing can dry hair.
If you’ve tried all this and your hair is still feeling damaged and dry, it might be time to seek the help of a professional. A salon will have access to products and treatments that you do not and can help restore your hair.
Of course – the absolute last resort is cutting your hair off! We hope you won’t have to resort to this more extreme solution. Read and follow the instructions that come with your hair dye. When in doubt, do not leave hair dye in for longer than 45 min!
