Hyaluronic acid is the most used ingredient in skincare. It's also the most misapplied. Most people apply HA to dry skin in a dry environment, then seal with nothing. The result: hydration that lasts 20 minutes and the feeling that the product doesn't work. The problem isn't the ingredient — it's the application.

Molecular Weight: The Variable Nobody Explains

HA isn't one ingredient — it's a family of molecules with molecular weights ranging from 50 kDa to over 1500 kDa. Each size acts at a different depth:

• High molecular weight (>1000 kDa) — forms a hydrating film on the surface. Immediate and visible plumping effect. Doesn't penetrate.
• Medium molecular weight (100–500 kDa) — penetrates the stratum corneum. More lasting, less superficial hydration.
• Low molecular weight (<50 kDa) — penetrates to the superficial dermis. Deeper hydration, anti-ageing effect.

The best serums combine all three. Those with only one offer one dimension of hydration.

The Protocol That Doubles HA Efficacy

1. Wash your face with lukewarm water
2. Don't dry completely — leave skin slightly damp
3. Apply HA serum within the first 60 seconds
4. Seal immediately with an occlusive moisturiser

HA in Dry Environments: The Paradoxical Effect

In environments with relative humidity below 40%, high molecular weight HA can draw water from deep dermal layers towards the surface — where it evaporates. In this case, applying HA without an occlusive in a very dry environment can paradoxically dehydrate the skin.