Hyaluronic Acid: The Complete Skincare Guide
Hyaluronic acid is one of the few skincare ingredients with near-universal agreement among dermatologists. Here's how it works, why molecular weight matters, and the one mistake that makes it backfire.
Hyaluronic acid (HA) is a naturally occurring polysaccharide found throughout your body — it's particularly concentrated in skin, joints, and eyes. One gram of HA can hold up to 6 liters of water, making it the most effective hydrating agent known in skincare.
Your skin's natural HA content decreases by about 50% between ages 20 and 50, contributing to the loss of plumpness and elasticity associated with aging.
Why Molecular Weight Matters
Not all hyaluronic acid in skincare works the same way — and this is where most products differ significantly.
- High molecular weight HA (>1,000 kDa): Cannot penetrate the skin. Sits on the surface, forming a hydrating film that prevents water loss. Provides immediate plumping effect.
- Medium molecular weight HA (100–1,000 kDa): Penetrates to the upper dermis. More lasting hydration effect.
- Low molecular weight HA (<100 kDa): Penetrates deeper into the dermis. Stimulates collagen production at deeper levels. Some research suggests potential irritation at very low weights.
The best products use multiple molecular weights for hydration at all depths. The Ordinary Hyaluronic Acid 2% + B5 (at $9) is one of the few affordable products that does this correctly.
The One Mistake That Makes HA Backfire
Best Hyaluronic Acid Products
The Ordinary Hyaluronic Acid 2% + B5
Three molecular weights, vitamin B5, $9. The benchmark affordable HA serum that outperforms products 10x its price.
SkinMedica HA5 Rejuvenating Hydrator
5 forms of HA at different molecular weights plus a time-release delivery system. Medical-grade, used post-procedure. Significantly more expensive but considered best-in-class by aesthetic practitioners.
Neutrogena Hydro Boost Hyaluronic Acid Serum
Affordable drugstore option with pure HA in a lightweight gel. Non-comedogenic, fragrance-free. Good option if The Ordinary isn't available locally.