how long should you leave hair dye in
I would imagine most semi-and demi-permanent dyes are about the same. If you are using a vegetable dye (such as manic panic, special effects, or henna) you may leave on as long as you want, from 30 minutes to overnight.
Most permanent dyes process in about 25-30 minutes.   I would imagine most semi-and demi-permanent dy â¦ es are about the same.   If you are using a vegetable dye (such as manic panic, special effects, or henna) you may leave on as long as you want, from 30 minutes to overnight.