Chronic pain is pain that lasts longer than three months and is often called persistent or long-term pain. It is usually described as 'pain that continues beyond the expected healing time after an injury or illness', as most tissues tend to heal within about three months in typical cases.
Chronic pain is thought to happen when the nerves and pain pathways become over-sensitive and keep sending danger signals to the brain, predicting pain even when there is no new injury or when the original injury has already healed. The brain then keeps responding to these signals and producing pain, a bit like a broken record that keeps repeating the same track.
Another way to understand this is to imagine pain as a fire alarm in the body. With chronic pain, the alarm keeps going off even though the fire (the original tissue damage) has already been put out.
Over time, the brain can get stuck in this pattern and needs fewer and fewer signals to create the feeling of pain. People can become over-sensitive to pain, and the pain can become so constant and overwhelming that it starts to feel like the new “normal”, even though the pain signalling system is now misfiring and trying to protect against a threat that is no longer there.