How long does permanent hair color last until it needs to be reapplied?

Permanent hair color is designed to provide a long-lasting change to the hair's color, which means it doesn't wash out or fade like temporary or semi-permanent dyes. Instead, the color remains in the hair until the hair grows out. As hair grows, the roots will show the natural hair color, which will necessitate reapplication to maintain a consistent look. This ensures that as the hair grows, the colored hair is eventually replaced by new, untreated hair.

While fading can occur depending on factors like the hair's exposure to sunlight, washing, and the type of products used on it, the fundamental characteristic of permanent hair color is that it isn't meant to wash out on its own, making the growth of new hair the primary reason for reapplication. Other options suggesting a time limit or based on other treatments do not accurately reflect the nature of how permanent color functions.