Sepsis can be caused by an infection in any part of the body which may enter the bloodstream causing rapid spread of bacteria and a systemic response. Even an infected tooth can cause sepsis, but it is much more common for sepsis to occur when a person is fighting an internal infection such as a urinary tract infection or pneumonia.

Sepsis also commonly occurs in when a patient is already in a hospital, either with a major infection or recovering from a major surgery as they are exposed to more illness and the patients are in a condition where their ability to fight infection is decreased (immunosuppressed).

Sepsis itself may be mild and curable, but when the body does not respond to treatment or when left untreated entirely, sepsis can quickly become severe which can lead to multiorgan failure and fatally low blood pressure, a condition known as septic shock.