Hair aging happens at the follicle level — and it shows in five ways: dryness, dullness, lack of volume, lack of thickness, and frizz. The Kérastase Chronologiste Bundle addresses all five in one limited-edition three-step ritual. The Bain Régénérant shampoo cleanses and preps the hair shaft for treatment; the Masque Régénérant delivers intensive regeneration in five minutes; and the new Overnight Youth Serum — applied before bed and left in — works through the hair's natural overnight repair cycle to restore vitality, shine, and resilience while you sleep. Three steps, one complete anti-aging ritual, for hair that looks and feels measurably younger with consistent use.