Algesia is a scientific term that refers to the ability to sense pain. Commonly, in medicine, the word is used to refer to levels of pain that are above those expected from a specific condition. Causes include damage to nerves and sensation receptors, some psychiatric conditions and narcotic drug use. Drugs that can help reduce algesia are known as analgesics.
Pain is an evolved response to damage to the body. When a finger touches a hot surface, for example, the heat damage to the skin is sensed by pain receptors on the skin. Pain stimulus passes up the nerves to the brain, which yanks the finger away. Even after the person has removed the finger, the damaged skin still produces pain signals, because the skin's ability to protect the finger against health issues like microbial infection is compromised. The pain, therefore, prevents the person from making the slight injury worse by using the finger.
Normally, each injury produces a specific level of pain, which puts a certain level of restrictions on the person's movements and actions. A person with a broken finger can make his or her own way to hospital, for example, whereas one with a broken leg typically has to stay still and wait for help. The lower level of pain with the broken finger allows free movement, as the risk of further damage is low by moving. Trying to walk on a broken leg, however, can cause serious damage and thus the body produces lots of pain to prevent this.
When a person experiences more pain than is usual with a certain medical condition, this situation is often called algesia. It may also be known as hyperalgesia. A hypersensitivity to pain may be due to damage in the bodily systems that recognize pain, or it may be due to psychological factors, in which the person affected has no physical reason for the increased pain, but rather the psychological recognition of pain is altered.
As it is sensory receptors and nerves that recognize and transfer pain information to the brain, it is these components of the body that are commonly involved in algesia conditions. People that have abused drugs of the opioid family, which includes heroin and morphine, can also suffer from algesia, as these drugs act directly on the pain sensation system of the body. A stroke can also produce abnormally high pain sensations, if the part of the brain that handles these pain signals is affected.
Analgesics are drugs that are primarily designed to reduce pain. Two major groups of these painkillers are non-steroidal anti-inflammatory drugs (NSAIDs) and narcotic drugs. Typically, NSAIDs like aspirin and ibuprofen fall into the over-the-counter drug category, whereas the narcotics, with their stronger effect, are more controlled. Examples of narcotics include codeine and morphine.