Soap Cap Time

Shampoo and peroxide mixture
Q: How long should you leave a soap cap in your hair? I am going to use 40-volume because I don’t want to do this several times. I want to try and do it in one shot.
The problem is the last 1 ½ to 2 inches of my hair is darker than the rest. A lady at the beauty store told me to leave it on for 5 minutes but I want to make sure she told me correctly.

A: Well, I can certainly understand your desire to avoid having to repeat a process over and over just to get the results you want, but you really want to be careful not to damage your hair in the process.
The exact amount of time you need to leave the soap cap on the hair is dependent on how your hair responds to the soap cap. Some people’s hair is resistant and takes longer to process, since the solution takes longer to penetrate the hair shaft.
For those who don’t know, a soap cap is a mixture of shampoo and peroxide developer (usually 20-volume) in equal parts and is used to gently lighten the hair’s color and refresh highlighted hair. When applied to the new growth of hair that has been highlighted, allowed to process for a short period then worked through the hair, the process is called “Breaking the Base”.
If you want to avoid doing the whole head over and over until you get the right result, try doing a strand test. Cut two locks of hair from an inconspicuous place on the head and secure the cut ends with tape. Apply the soap cap mixture to one lock and leave the other alone for comparison. Process the “test strand” in 5 minute increments and dry the strand between applications.
Repeat the application and processing until you get the results you desire, adding up the amount of time it takes to get the results. This will give you an idea of how long you can safely process the soap cap on your hair and how quickly the hair will respond. It will also show you the texture of your hair afterward, so that you can make adjustments as needed.
Photo: Doro Guzenda/Shutterstock
See also:
Highlights Q&A
Hair color fixes
The formula for breaking the base
Can you really lighten your hair color with dish soap?