Algae is an informal term for a large, diverse group of organisms that includes more than 20,000 different known species. Algae are very simple organisms that have chlorophyll as their primary photosynthetic pigment. In skin care products, algae extract has several functions, including as a thickening agent, water-binding agent, and antioxidant. Some species of algae even provide powerful anti-aging effects when applied to the skin.