Major classes of shock include:

• cardiogenic shock (associated with heart problems)
• hypovolemic shock (caused by inadequate blood volume)
• anaphylactic shock (caused by allergic reaction)
• septic shock (associated with infections)
• neurogenic shock (caused by damage to the nervous system)

Shock is caused by any condition that dangerously reduces blood flow, including:

• Heart problems (such as heart attack or heart failure)
• Low blood volume (as with heavy bleeding or dehydration)
• Changes in blood vessels (as with infection or severe allergic reactions)

Shock is often associated with heavy external bleeding from trauma or serious injury. Internal bleeding, however, cannot be seen but can still cause shock. This could occur from a damaged blood vessel that ruptures. Spinal injuries can also cause shock.

Toxic shock syndrome is an example of a type of shock from an infection.