Understanding Skin Hydration

Hydration is the water content of the stratum corneum. Healthy skin holds roughly 20–30% water in this layer; below about 10%, it becomes visibly flaky and less flexible. Maintaining that water depends on two things: attracting it, and keeping it from leaving.

Dry versus dehydrated

Dry skin is a type — it produces less sebum. Dehydrated skin is a state — it lacks water, and can occur in any skin type, including oily. Oily-yet-tight skin is a common sign of dehydration. The distinction matters because dry skin needs lipids, while dehydrated skin needs water and something to hold it.

The three mechanisms

• Humectants attract water: hyaluronic acid, glycerin, urea, snail mucin
• Emollients smooth and soften by filling gaps between cells: fatty acids, ceramides, plant oils
• Occlusives form a film that slows evaporation: petrolatum, squalane, shea butter, dimethicone

The Asian skincare approach

Layering several thin, water-rich products — essence, toner, serum — followed by a moisturizer follows this logic closely: humectants first, then lipids and occlusives to seal. It is why the 'seven skin method' and similar practices emphasize applying hydrators to damp skin.

From the library · Book 1

The Art of Radiance: The Secrets to Asian Style Skincare

Chapter 7 — Hydration & Barrier Repair

A Comprehensive Guide to Asian Style Skincare and New Trends