What Does Bleach Do?
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What does bleach do? Doesn't it make your hair blonde? I have a friend who used bleach and it looked really bad. I really don't want my hair to be fried. Can you explain to me the difference?
In your case, if the hair color product you used before gave you the results you like, I see no reason to change things on a second go around. When color is mixed with developer into a lightening formula, that formula has a life-span which minimizes its efficacy and therefore the amount of damage it can do.
Bleach on the other hand, keeps working as long as it is moist, and can easily over-process, resulting in damaged hair if you aren't sure of how quickly your hair processes.
I generally advise leaving the bleach applications to professionals.
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See also:
Bleach hair
How to color hair
Bleaching retouch and hair breakage
What is hair bleach made of? Is bleach harmful to your health?