败血症（英语：Sepsis）指的是由于感染所引起的全身性发炎的严重疾病。常见的临床症状包括发烧、呼吸频率和心跳加速，以及意识不清。有时患者也会发生特定的临床症状，如因肺炎引起的咳嗽，或因为肾脏感染所导致的排尿灼热感。若败血症发生于年长者、年纪幼小或免疫能力贫弱之患者，则可能会没有特定的感染症状，亦可能表现出体温过低或维持正常（一般发炎时，组织的温度会升高）的特殊症状。严重的败血症会导致供应组织的血流不足甚至器官衰竭。血流不足的原因可能是由于败血症引起的低血压、高血乳酸或是低排尿量所导致。败血症引起的低血压有可能会导致感染性休克，此一休克症状并无法借由静脉输液的方式有所改善。

Sepsis is a life-threatening condition that arises when the body's response to infection injures its own tissues and organs. Common signs and symptoms include fever, increased heart rate, increased breathing rate, and confusion. There may also be symptoms related to a specific infection, such as a cough with pneumonia, or painful urination with a kidney infection. In the very young, old, and people with a weakened immune system, there may be no symptoms of a specific infection and the body temperature may be low or normal rather than high. Severe sepsis is sepsis causing poor organ function or insufficient blood flow. Insufficient blood flow may be evident by low blood pressure, high blood lactate, or low urine output. Septic shock is low blood pressure due to sepsis that does not improve after reasonable amounts of intravenous fluids are given.