Why Use 7 Day Keratin Smooth Conditioner? This conditioner, as part of the 7 Day Smooth System, works with the heat of your straightener to transform unruly hair into salon-smooth hair that even lasts up to 4 washes.* You can easily create your style every day with less frizz and more manageability. Gentle enough for every day use and on colour treated hair. *with Shampoo, Conditioner and Treatment usage