10 and 20 are used to deposit colour on the hair for example used with a brown or red dye. 30 and 40 are used for lifting hair colour to a lighter shade.
I wouldn’t recommend 40, i never go over 30. 40 is very harsh on the hair and can cause a lot of damage. This is because 40vol contains 12% peroxide, while 30vol has only 9% peroxide. Which makes it harsher.
10 and 20 are used to deposit colour on the hair for example used with a brown or red dye. 30 and 40 are used for lifting hair colour to a lighter shade.
I wouldn’t recommend 40, i never go over 30. 40 is very harsh on the hair and can cause a lot of damage. This is because 40vol contains 12% peroxide, while 30vol has only 9% peroxide. Which makes it harsher.
40 is most harsh on the hair…its used more for black hair .
It means how many shades it can lift, 20 lifts 2 shades, 40 volume is mainly used for going blonde, and 20 and 30 more for darker color dyes.