Hair dyeing is a common practice used to change the color of one's hair. The duration for which hair dye should be left in varies depending on several factors, including the type of dye, the desired color change, and the condition of the hair.
Permanent hair dyes typically require a longer processing time, ranging from 20 to 45 minutes. These dyes penetrate the hair shaft and alter its natural pigment, resulting in a more permanent color change. Semi-permanent dyes, on the other hand, have a shorter processing time of around 15 to 25 minutes. They deposit color on the hair's surface without altering its natural pigment, leading to a less permanent color change.