Vitamin C serums are a cornerstone of effective skincare, offering powerful antioxidant protection, brighter skin tone and long-term collagen support. In this guide, we explore how Vitamin C works, why formulation matters, and why iS Clinical Pro-Heal Serum Advance+ — recognised by Cosmopolitan as one of the best Vitamin C serums of 2026 — remains a trusted, clinic-approved choice for healthy, resilient skin.