Overnight Youth Serum by Kérastase is a night treatment infused with Pro-Xylane™ and Ochrophyta Algae, designed to reverse the visible signs of ageing during nighttime. Targeting dryness, dullness, frizz, lack of volume and thickness, this leave-in serum delivers intensive overnight care. Just one pump to deliver powerful actives deep into the hair. Powered by Pro-Xylane™, a molecule known for its anti-ageing action, and Ochrophyta Algae, the fastest growing algae in the world, a bio-sourced deep sea treasure that captures the regenerative power of the ocean. Its transformative quick-break texture melds instantly into the hair's lengths, leaving a flawless finish and enveloping the hair with the signature Chronologiste fragrance that turns routine care into a luxurious ritual. Apply to dry or damp hair before bedtime. Spread one pump into hands and distribute evenly through lengths and ends. No need to rinse. Wake up to fuller, healthier looking, smoother hair*. *Consumer test after application of Bain + Mask + Night Serum, 90 Consumers