A liposome is a spherical vesicle composed of a bilayer membrane. Liposomes can be composed of naturally-derived phospholipids with mixed lipid chains or of pure surfactant components. Liposomes usually (but not always) contain a core of aqueous solution. Lipid spheres that contain no aqueous material are called micelles. A liposome can encapsulate different substances inside the “droplet” and, in this manner, act like a delivery system. Liposomes are useful for stabilizing ingredients that are sensitive to degradation when exposed to air.