Research Glossary

The outermost protective layer of the skin (stratum corneum) that regulates moisture and protects against irritants.

The rate at which water passes through the skin to the surface and evaporates. A key marker of barrier function.

An ingredient that draws moisture from the environment or deeper skin layers to the surface. Examples: hyaluronic acid, glycerin.

An ingredient that softens and smooths the skin by filling gaps in the barrier. Examples: squalane, fatty alcohols.

An ingredient that forms a physical barrier on skin to prevent moisture loss. Examples: petrolatum, dimethicone.

An agent that softens and helps shed dead skin cells (keratinocytes). Examples: AHAs, BHAs.

A study design where participants are randomly assigned to treatment or control groups. A strong evidence type for skincare research.

A trial design where each side of the face receives a different treatment, using the subject as their own control.

The base formulation used in a study without the active ingredient. Used as a placebo comparator.

A study design where some participants receive an inactive control (placebo) to allow comparison with the active treatment.