Toning your hair twice can be beneficial in some cases, but it can also have negative effects. Repeatedly toning your hair can help to remove any remaining brassiness or yellow tones, and it can also help to maintain the vibrancy of your hair color. However, toning your hair twice can also cause your hair to become dry and damaged, especially if you use a toner containing harsh chemicals. Additionally, toning your hair frequently can lead to an uneven or unnatural-looking color. It is always best to consult with a hair professional before toning your hair twice to determine if it is safe and appropriate for your hair.