An embolism occurs when an object or embolus migrates from one part of the body through the blood vessels and causes blockage in a blood vessel in another part of the body. An embolus that migrates through the vascular system to the brain will likely cause an ischemic stroke. Foreign substances that can cause an embolism include a blood clot, an air bubble, amniotic fluid, a globule of fat, a clump of bacteria, chemicals (such as talc), and drugs (mainly illicit ones). Blood clots are the most common cause of embolism. Embolism can be contrasted with a thrombus which is the formation of a clot within a blood vessel, rather than being carried from somewhere else. Prevention and treatment for embolism vary depending on specific pathology (e.g., fat, air, bacteria, and blood clot) and source (e.g., bone fracture, cardiac, surgical procedure, and atherosclerotic plaque).