The Complete Handbook of Lotion & Moisturizer

Chapter 1: Understanding Lotion & Moisturizer

Lotion and moisturizer are terms most people use interchangeably, and both serve the same essential function: they deliver water to the skin and help prevent that water from evaporating. But beyond this basic purpose, they are not simple products. They are engineered emulsions—complex systems where oil and water, which naturally repel each other, are forced into a stable mixture with the help of emulsifiers and preservatives. How well they work depends on their specific formulation, how they're applied, the condition of the skin barrier they're applied to, and the environment in which they're used. Understanding what they actually do, at a mechanical level, is the foundation for everything else in this handbook.

What Lotion and Moisturizer Actually Are

A moisturizer is any product that increases or maintains skin hydration. It does this through two mechanisms: humectancy and occlusion. A humectant is an ingredient—typically glycerin, propylene glycol, or hyaluronic acid—that draws water from deeper skin layers and the environment toward the skin surface. An occlusive is an ingredient or product layer that physically seals the skin to prevent water loss through evaporation. These two mechanisms work differently, and no moisturizer relies on only one.

A typical lotion might be 50% to 80% water, with the remainder consisting of oils, emulsifiers, thickeners, preservatives, and active ingredients. A cream contains less water (typically 20% to 50%) and more oil, making it thicker and more occlusive. A body oil is almost entirely occlusive and contains no significant water.