Pain comes in many forms. The sudden, sharp, and usually temporary pain produced as a result of getting a finger caught in a door is quite different than the dull throbbing pain of a backache that doesn't go away. Though they are both painful sensations, a pinched finger and a backache feel very different.
The way the body responds to pain depends on the nature of that pain. For example, a sudden injury will release a flood of pain-suppressing chemicals such as adrenaline. This response is not specific to pain: the same types of chemicals and hormones that are released as a result of a sudden injury are also released when you are frightened. It is part of the body's "fight or flight" system. Watching a suspenseful scene in a movie has the same effect. And just like the fear felt in a movie, the pain of a minor injury, such as a small cut, doesn't usually last long and the release of adrenaline and other chemicals subsides.
It's impossible to be in terror for long, and your body adjusts. For the same reason, though a back injury may have initially been associated with the release of these hormones, a constant backache will not trigger the same chemical response from the body. The body adapts to these hormones since we cannot sustain a constant fight or flight response.
There are several ways to describe and define different types of pain. Pain can be categorized in terms of its mechanism and/or its duration.
Pain categorized by mechanism
Pain can be categorized into two main types; nociceptive pain and neuropathic pain.
Nociceptive pain is the ordinary sensation that arises from injury or damage to some part of the body other than the nerve tissue itself. Specialized nerve endings at the injury or damaged site of the body are activated and send messages to the brain.
Neuropathic pain (nerve pain) arises from the nervous system itself, either as a result of injury or disease to the nerve tissue. It tends to be more difficult to treat than nociceptive pain. Because the nerves are not functioning properly, they may transmit the sensation of pain to the brain even after the original injury has healed. Neuropathic pain is frequently described as a burning or shooting sensation and can lead to a heightened sensitivity to stimuli, even to the point of a gentle touch being interpreted as painful. This pain response to a non-painful stimulus is called allodynia, and an exaggerated pain response to a painful stimulus is called hyperalgesia.
Damage to the nerves themselves can lead people to have pain in a part of their body that may not even exist anymore. For example, phantom limb pain can be associated with burning and shooting pain in the leg/foot that has been amputated.
Pain categorized by duration
Commonly, pain is categorized in terms of duration - essentially, how long the pain lasts and how quickly it disappears. Using this classification: acute pain is short-term, chronic pain is long-term, and recurrent pain refers to intermittent painful episodes. For example, a child who has repeated headaches is suffering recurrent pain.
These pain types are not mutually exclusive: people can have acute pain as well as chronic pain at the same time. Acute pain, especially if not properly managed, can become chronic pain.