Ingredient Deep Dive

Hyaluronic Acid Isn't Just "Hydration"

Molecular weights, humectant science, and why HA can actually make your skin drier in the wrong conditions.

January 27, 2026

9 min read

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The HA Paradox

Hyaluronic acid can hold up to 1,000x its weight in water—which sounds incredible. But here's what most people don't realize: HA is a humectant, not a moisturizer. This distinction is everything.

In dry environments, HA can actually pull water out of your skin instead of into it.

How Humectants Actually Work

In Humid Environments

HA pulls moisture from the humid air into your skin. This is the ideal scenario—you get plumping and hydration.

Result: HA works beautifully ✓

In Dry Environments

When the air is drier than your skin, HA has nothing to pull from the air—so it pulls water from the deeper layers of your skin instead.

Result: HA can dry you out ✗

Molecular Weight Matters

Not all HA molecules are the same size—and size determines what the HA actually does:

High Molecular Weight (>1,000 kDa)

Sits on skin surface • Forms hydrating film • Immediate plumping • Can't penetrate

BIG

Medium Molecular Weight (100-1,000 kDa)

Partial penetration • Balanced benefits • Good all-rounder

MED

Low Molecular Weight (<100 kDa)

Penetrates deeper • Longer-lasting hydration • Can be slightly pro-inflammatory

SM

Best Approach: Multi-Weight HA

Look for products with multiple molecular weights to get benefits at different depths. Many quality serums now include a mix of high, medium, and low weight HA.

The Essential Rule: Humectant + Occlusive

This is the most important thing to understand about HA:

Always seal HA with an occlusive layer!

Humectants (Pull Water)

• Hyaluronic acid
• Glycerin
• Propylene glycol
• Urea
• Aloe vera

Occlusives (Seal Water In)

• Petrolatum
• Mineral oil
• Silicones (dimethicone)
• Squalane
• Shea butter

The formula: Apply HA serum to damp skin → follow with moisturizer containing occlusives → this locks the hydration in.

How to Use HA Correctly

1

Apply to Damp Skin

Give HA water to grab onto. Apply right after cleansing while skin is still slightly wet.

2

Follow Immediately with Moisturizer

Don't let HA dry on its own. Lock it in with an occlusive moisturizer within 60 seconds.

3

Consider Your Environment

In very dry climates (desert, winter heating), you may need heavier occlusives or to skip HA entirely.

Key Takeaways

HA is a humectant, not a moisturizer—it attracts water but can't retain it alone
Multi-weight formulas provide benefits at multiple skin depths
Always seal with occlusive—or HA may dry you out
Apply to damp skin for best results
Environment matters—adapt your routine to humidity levels

Disclaimer: This article is for educational purposes only and is not intended as medical advice. The information presented is based on generally accepted skincare science, but individual results may vary. Always consult a board-certified dermatologist or healthcare provider before making changes to your skincare routine, especially if you have existing skin conditions.

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