If you are planning to lighten your hair for up to 3 or 4 shades, you’ll need both bleach and a developer, although a developer alone may be able to do the job, especially if you’re not planning on a drastic change (think 1 shade lighter). You also won’t need a bleach if you’re just applying hair dye without lightening your hair.
So, how long to leave bleach in hair 30 vol? The answer is, it’s up to you and how light you want your hair to be, as long as you don’t leave it on for more than 30 minutes! And, remember to keep the developer and bleach ratio at 2 to 1. After bleaching, moisturize, moisturize, moisturize!