That expensive hyaluronic acid hair serum you've been considering might not be worth the splurge. In this episode, Dr. Elena Voss breaks down the molecular science behind two popular hair hydrators—hyaluronic acid and glycerin—to reveal which one actually delivers results and which one is mostly marketing hype. Whether you're battling frizz, dealing with dry strands, or just trying to stretch your beauty budget further, this deep dive into humectant chemistry will change how you shop for hair products.

• Both hyaluronic acid and glycerin work on the hair's surface at the cuticle level—neither truly penetrates to hydrate from within, despite marketing claims suggesting otherwise.

• Glycerin at 92 daltons is far smaller than hyaluronic acid (50–3,000 kilodaltons), allowing it to slip between lifted cuticle scales, but  ...