Toner is a semi-permanent hair color that is used to deposit color, correct unwanted tones, and enhance the overall appearance of hair. Unlike permanent hair color, toner does not contain ammonia and is less damaging to the hair shaft, making it a popular choice for those looking to make a subtle change to their hair color or refresh their current shade. The duration of time toner should be left in the hair depends on several factors, including the desired level of color deposit, the porosity of the hair, and the specific toner being used.
Generally, toner should be left in the hair for a minimum of 10 minutes to allow the color pigments to penetrate the hair shaft. However, for more intense color results, toner can be left in for up to 30 minutes. It is important to follow the manufacturer's instructions carefully, as leaving toner in the hair for too long can lead to over-toning, which can result in brassy or unwanted tones.