Confused about skin-care terminology? Here's what several common terms mean:

Collagen. A protein that contributes to the elasticity of skin tissue.

Emollient. A lotion or cream that helps make skin smoother and softer.

Exfoliant. Any product that helps to remove dead cells from the skin's surface.

Humectant. A product that promotes the retention of moisture in the skin.

Hydration. The process of bringing more water into skin tissues.

SPF. Stands for sun protection factor, a numeric scale used to establish the effectiveness of a product at blocking the harmful rays of sunlight from reaching the skin. The higher the number, the greater the protection.

AHA. Stands for alpha-hydroxy acid. A natural acid, often derived from fruit, that helps slough off dead skin and speed up cell renewal. AHAs have emerged as one of the most important ingredients in skin care.