Chronic pain, also called persistent or long-term pain, is pain that persists or recurs for more than three months. This definition is temporal rather than a statement that the pain must have a particular intensity, location or cause. Chronic pain may follow an injury or disease that remains active, may continue after an original injury has healed, or may occur without a single identifiable structural explanation.
NICE distinguishes chronic primary pain, where no underlying condition adequately accounts for the pain or its impact, from chronic secondary pain, where an underlying condition does adequately account for it; the two can coexist. Chronic pain is therefore a broad clinical category rather than one disease.
Chronic pain differs from acute pain not merely because it lasts longer but because its biological and functional meaning can change over time. Acute pain commonly serves an immediate protective role connected to tissue damage, whereas persistent pain can itself become a major health problem affecting sleep, mobility, employment, relationships, mood and participation in ordinary activities. Repeated or prolonged nociceptive input can contribute to changes in peripheral and central nervous-system processing, including sensitisation, although mechanisms differ between conditions. Pain may therefore persist even when the original tissue injury has substantially healed. This does not mean that chronic pain is imaginary or purely psychological. It means that pain is generated by a complex nervous-system experience influenced by biological, psychological and social factors.
Chronic secondary pain includes pain attributable to an ongoing or recurrent condition such as osteoarthritis, rheumatoid arthritis, endometriosis, inflammatory bowel disease, persistent neuropathy or another identifiable disease. Chronic primary pain is different: the pain itself and its impact are the central clinical problem, and no underlying condition sufficiently explains them, or the pain or its impact is judged disproportionate to observable injury or disease.
NICE notes that chronic primary pain can coexist with chronic secondary pain and that an initial classification can change if the clinical presentation changes. This prevents the false assumption that finding no single structural explanation means that the pain is unreal. It also means clinicians should continue to reassess when new symptoms or clinical changes emerge.
Chronic pain can arise through several interacting mechanisms. Persistent nociceptive input can occur when damaged or inflamed tissues continue to activate pain pathways. Neuropathic pain results from disease or injury affecting the somatosensory nervous system and may produce burning, electric-shock-like, shooting, tingling or abnormal sensitivity. Nociplastic mechanisms describe altered pain processing in which pain can occur without clear evidence of ongoing tissue damage or a lesion explaining the symptoms. These mechanisms can overlap in the same person. For example, someone with arthritis may have nociceptive joint pain while also developing neuropathic symptoms from nerve involvement and central sensitisation. Accurate assessment therefore involves understanding the pain mechanism rather than assuming that every chronic pain syndrome has a single cause.
Chronic pain can affect virtually every dimension of health. Persistent pain may restrict walking, exercise, work, education, household tasks, sexual activity and social participation. Sleep can become fragmented, while poor sleep can increase pain sensitivity and fatigue, creating a reinforcing cycle. Persistent pain can also be associated with anxiety, low mood, frustration and reduced confidence, but these associations do not mean that psychological factors are the sole cause.
NICE recommends assessment of how pain affects daily life, sleep, physical and psychological wellbeing, stressful events, existing coping strategies and relevant social circumstances. A person-centred assessment therefore considers both what the pain does to someone's life and what aspects of life may in turn influence the experience of pain.
Chronic pain is assessed primarily through clinical history and examination rather than through a single definitive laboratory test or scan. Important information includes onset, duration, distribution, quality, severity, triggers, relieving factors, functional effects, neurological symptoms, systemic symptoms, previous illnesses, medicines and previous investigations. Tests are selected according to the suspected cause rather than performed simply because pain is chronic.
Imaging can identify structural abnormalities, but abnormalities on scans do not necessarily explain the severity of symptoms, while normal investigations do not invalidate pain. NICE emphasises identifying potentially treatable underlying disease while simultaneously assessing the person's experience and functional impact. Reassessment is appropriate when symptoms change or flare because the initial diagnosis may need to be reconsidered.
Management depends on whether pain is primary, secondary, neuropathic, inflammatory, musculoskeletal, visceral or another defined type. Treating an underlying disease may reduce secondary pain, while chronic primary pain is generally managed through strategies aimed at improving function, quality of life and symptom control rather than promising elimination of pain.
NICE recommends supervised exercise programmes for chronic primary pain and considers cognitive behavioural therapy or acceptance and commitment therapy, acupuncture in specified circumstances, and selected antidepressants after discussion of benefits and harms. NICE specifically advises against initiating several medicines, including opioids, paracetamol, NSAIDs and gabapentinoids, solely to manage chronic primary pain. These recommendations do not mean those medicines are inappropriate for every form of chronic pain; treatment must follow the specific diagnosis and relevant guideline.
A major misconception is that chronic pain necessarily indicates continuing physical damage or, alternatively, that unexplained chronic pain is merely psychological. Neither assumption is accurate. Chronic pain can involve ongoing disease, persistent nerve injury, altered nervous-system processing, or combinations of mechanisms, and the absence of a single explanatory lesion does not make the experience less real.
Chronic pain is now explicitly recognised in international disease classification, and NICE uses the distinction between chronic primary and chronic secondary pain to reflect different clinical situations. The practical goal is often not simply to achieve a zero pain score but to improve function, sleep, participation, wellbeing and control while addressing treatable causes and avoiding unnecessary investigations or harmful long-term medication.
