New sealed in box Kerastase Serum Therapiste Dual Treatment Hair Serum. Leave-In repairing hair serum for weak, over-processed and damaged hair. For extremely damaged lengths and ends. Apply 1-2 pumps of Serum Therapiste from mid-lengths to ends on towel-dried hair. Leave in and proceed to blowdry as usual. Can also be used as a finishing touch on dry hair to control flyaways and seal split ends. 30 ml / 1.01 fl. oz.