how long should i leave purple shampoo in

The general recommendation is to leave purple shampoo in for about 1 to 5 minutes, depending on the brand and how much toning you want. For minimal neutralizing of brassiness, closer to 1-3 minutes is fine, while for stronger yellow neutralizing, 3-5 minutes or even up to 15 minutes can be used depending on hair type and tone goals. Leaving purple shampoo on for longer, such as up to an hour, can intensify the toning effect but may risk purple tint buildup or drying out the hair, so it is not usually advised daily and should be done with caution. For best results, follow the instructions on the specific product used and adjust based on your hair's response and desired tone.