“A double process is a bleach-on-root application, also known as a global application. This process should be done every three to four weeks or when you have ½ an inch of regrowth,” Paglionico says. “This needs to be done more often, because the bleach is applied directly to the scalp, which warms up the bleach and helps it to develop faster.”
“If you wait too long, the temperature drops and the hair may not get as light as the last application. This can create a warm band,” she adds.
However, this process is very demanding and puts your hair at risk for more breakage, Paglionico notes. Translation: Double-process jobs aren’t the best idea for anyone with brittle strands already.