A fat embolism is a large fat droplet that enters the blood stream. A fat embolism occurs most commonly following a fracture of the pelvis, femur, or tibia. Multiple fractures are more likely to lead to fat embolism than single fractures.

Symptoms of fat embolism occur when the small fat droplets obstruct the small vessels in the lung or brain. The obstruction reduces the blood flow to parts of the lung or brain, causing those areas to malfunction.

Symptoms of fat embolism usually begin 12 to 72 hours following the injury.