How often does red hair color need to be touched up?

Consistent touch-ups every four to five weeks are important with reds. If you wait too long between touch-ups—i.e. when new growth is over half an inch—your body heat may process the color closest to the scalp faster, resulting in what professionals call "hot roots,” when the color at the scalp is brighter than at the mid-length or ends. To give red hair color a boost between salon visits, try a color enhancing shampoo.