During a lightener retouch, what part of the hair is lightened first?

In the context of a lightener retouch, the new growth is the area that is lightened first. This is because new growth is the hair that has not been previously processed and is often darker than the rest of the hair that has already been lightened. When performing a lightener application, it's crucial to start with the new growth to ensure even color throughout the hair.

If the lighter product were applied directly to the ends or mid-lengths first, those areas could over-process while waiting for the new growth to lighten adequately. This can lead to uneven results and potential damage to the hair. Always prioritizing the new growth allows for a balanced and consistent outcome.