Exosomes are microscopic, round, or oval sac-like structures that contain proteins, lipids, RNA, and DNA. They’re produced inside the cell by almost all cell types, and are released into the extracellular space, the space outside the cell. They’re about one 100th the size of a human cell and are also known as Extracellular Vesicles (EVs). A vesicle is a small sac-like structure.