Hydration vs. Moisturization: The Biochemistry of Skin Balance
In cosmetic science, hydration and moisturization are distinct yet complementary processes. While often used interchangeably in marketing, they play very different biochemical roles in maintaining a healthy stratum corneum and functional skin barrier.
Hydration: Water Content Within the Skin
Hydration refers specifically to the water content stored in corneocytes. These are the cells of the outermost skin layer. Well-hydrated corneocytes are plump and flexible, creating a smooth skin surface. This water is important for:
Enzymatic activity: Hydration activates enzymes responsible for natural shedding of dead cells, also known as desquamation. When hydration levels are low, desquamation becomes irregular, resulting in dry skin. This typically shows up as flakiness or scaling.
Barrier repair: Enzymes that build cholesterol, free fatty acids, and ceramides are supported by water.
Stratum corneum health: Sufficient hydration improves skin elasticity and reduces the appearance of fine lines.
A few signs of dehydration include more pronounced fine lines, dullness, tightness, flakiness, and flat skin.
I thought it’d be helpful to list out a few key ingredients. In cosmetic science, we refer to hydrating ingredients as humectants. A few examples include:
Hyaluronic Acid
Glycerin
Sodium PCA
Panthenol
Humectants draw water from the dermis or environment into the stratum corneum, replenishing hydration. However, it is important to note that without moisturization, that water can quickly escape.
Moisturization: Protecting the Barrier
Moisturizing helps strengthen your skin’s natural barrier. This barrier is made of lipids that work like “mortar” holding your skin cells together. It keeps your skin hydrated by locking in moisture and protects it from environmental stressors.
A few signs of dryness include flakiness, rough texture, irritation, sensitivity, or visible cracks in the skin barrier.
A few moisturizing ingredients that we use include ceramides, fatty acids, butters, dimethicones, squalene, and mineral oils. In cosmetic science, we refer to these as emollients or occlusives.
Unlike humectants, these ingredients don’t add water to the skin. Instead, they lock in hydration and protect against evaporation.
Hydration + Moisturization: A Two-Step Approach
For optimal skin health, both hydration and moisturization must be addressed together:
1. Hydration Step: Use serums or toners containing humectants to replenish water in the stratum corneum.
2. Moisturization Step: Apply a cream or lotion rich in emollients and occlusives to trap that hydration and strengthen barrier lipids.
Analogy: Hydration fills your skin’s “water tank,” while moisturization acts as the lid, locking in that moisture so it doesn’t escape.
Final Takeaway
Hydration and moisturization are not redundant terms, nor are they the same. Although they work together, they address two different, vital needs of the skin. A well-curated routine provides hydration to replenish water and emollients/occlusives to seal it in. You need both, friend!
In beauty & chemistry,
Andria
