Narrator: This is Science Today. Researchers have discovered an important link between post-operative pain and infection. Dr. Daniel Sessler, a professor of anesthesia at the University of California, San Francisco, discovered that completely controlling pain with medication not only improves patient comfort, but also significantly reduces the risk of infection.

Sessler: Tissue oxygen is known to be the most important factor influencing infection. The reason is that the primary defense against the bacteria that cause surgical infections are killed by neutrophils, which are a type of white blood cells and they depend on oxygen.

Narrator: But pain stimulates the body's protective fight or flight response. This chemical reaction limits the flow of oxygen-rich blood to tissues such as the skin; so more oxygen can go to the brain and other organs necessary in emergencies.

Sessler: However, in post-operative surgical patients, those same responses are not helpful and it's best to use effective pain treatment to block the fight or flight response.

Narrator: For Science Today, I'm Larissa Branin.