Altered pain states

At the site of an injury sensory responses can be exaggerated:

- Noxious stimulation becomes extra painful than usual (hyperalgesia)
- Mechanical or thermal stimuli which are generally innocuous become painful (allodynia)
- Pain can take place in the absence of any stimulus (spontaneous pain)

When transient these have a protective role in encouraging guarding of the site of injury, but when prolonged they are pathological. These states arise because neurons become more excitable—their thresholds are lowered—a process called sensitization. Inflammation is often a major factor (inflammatory pain). Damage to pain pathways per se is termed neuropathic pain.