KOSÉ COSME DECORTE AQ Boosting Treatment Hair Serum 200mL The answer: a "pre-treatment serum" for your hair. A hair serum born from the wisdom of dermatological research. Its effective water-based formula penetrates to the core of the hair, repairing damage. It locks in moisture within the hair, leading to smooth, manageable hair all the way to the ends, and a high-quality shine. The next morning, your hair is free of frizz, with a smooth, silky finish that feels great to the touch.