Hyperalgesia describes an increased sensitivity to pain. It can be caused either by damage to peripheral nerves, or to the parts of the synapse of nerve cells that react to pain. It is a normal response to an infection. It can effect anything from a localized area to the entire body. Localized hyperalgesia is usually a response to injury and occurs either within or immediately around the damaged tissues.
Hyperalgesia can also occur as the result of the use of narcotics for chronic pain.