What is Chronic Pain?

Chronic pain is defined as pain lasting three months or longer, often becoming a long-term condition. Rather than a singular, uniform condition, the term chronic pain represents a spectrum of disorders defined by prolonged pain caused by diverse underlying mechanisms. These mechanisms include nociceptive pain due to tissue damage and nociceptor activation, neuropathic pain due to disease or damage of the nervous system, and/or nociplastic pain, which arises due to altered nociception often characterised by hypersensitivity and increased pain perception (Bonezzi et al., 2020). Furthermore, chronic pain may be multifactorial, involving biological, physiological, psychological, or psycho-social factors. In some instances, it may occur without an identifiable or specific cause, a condition referred to as idiopathic pain (Rahman et al., 2023). Unlike physiological pain, which is elicited by a noxious stimulus, chronic pain lacks the beneficial role of protecting the body against injury or illness, making it pathophysiological (Dydyk and Conermann, 2024).

The Physiology of Pain

The nervous system consists of the central nervous system (CNS), which includes the brain and spinal cord, and the Peripheral Nervous System (PNS), which contains the nerves outside of the CNS. The PNS branches into the somatic nervous system for regulating voluntary actions, and the autonomic system for regulating involuntary movements.

Neurons are the main component of the nervous system, transmitting action potentials through neurotransmission. Afferent neurons carry sensory stimuli towards the CNS, with the thalamus relaying these signals to brain regions including the somatosensory cortex, amygdala, hippocampus, and prefrontal cortex for processing various sensory signals, including pain (Roldan-Valadez et al., 2023). Efferent neurons carry output from the CNS through the PNS towards muscles and organs, enabling a physical response, including reflex actions.

Nociception, derived from the Latin “nocere”, meaning “to harm”, is how the sensory nervous system detects noxious (harmful) stimuli to protect our organs and tissues. Nociceptors, specialised neurons, identify harmful stimuli including mechanical pressure, temperature changes, and chemicals. These signals sent to the brain result in pain perception (Cohen, Vase, and Hooten, 2021).

What is the Pathophysiology of Chronic Pain?

Although this overview of the nervous system is brief, it demonstrates the complexity of pain-related pathological processes that can occur within the human body. In some clinical circumstances, individuals may experience nociception activation without feeling pain, meaning the body detects potential harm, but the individual does not perceive it as painful. Counteractively, an individual may feel significant pain despite the absence of a measurable noxious stimulus, disease, injury, or other underlying cause (Zhou et al., 2020).

However, chronic pain is often associated with reduced neuroplasticity, the brain’s ability to functionally and structurally adapt (Puderbaugh and Emmady, 2021). Chronic pain can develop following significant trauma or nerve damage, such as post-surgery. It may also result secondary to other diseases, conditions, medications, or lifestyle factors such as obesity, unhealthy dieting, stress, smoking, poor sleep, and physical inactivity (Dydyk and Conermann, 2024;Nijs and Reis, 2022).

What are the Classifications of Chronic Pain?

Chronic primary pain is persistent pain without a clear underlying cause or pain that is disproportionate to any current injury or illness. Examples include chronic widespread pain, fibromyalgia, complex regional pain syndrome (CRPS), chronic primary headache or orofacial pain, chronic primary visceral pain, chronic primary musculoskeletal pain, chronic cancer-related pain, and chronic post-surgical or post-traumatic pain (Fenske, 2021).

Chronic Secondary Pain is persistent pain associated with or caused by an identifiable underlying condition. Examples include chronic central or peripheral neuropathic pain, chronic secondary visceral pain, chronic secondary headache or orofacial pain, and chronic secondary musculoskeletal pain (Korwisi et al., 2020).

Chronic pain has different classifications based on the cause, and an individual's medical history is mandatory to know to give a diagnosis of the form of chronic pain they may have. More information is available at National Institute of Health and Care Excellence: Classification | Background information | Chronic pain | CKS | NICE

Can chronic pain affect my mental health and lead to disability?

Under the Equality Act 2010, chronic pain is recognised as a disability, as it can affect daily functioning and an individual’s quality of life (UK Government, 2010). Pain caused by pathology can significantly influence mental health, contributing to heightened stress levels that can lead to anxiety, depression, irritability, insomnia, inattention and obsessive thoughts. Furthermore, mental health issues can exacerbate pain symptoms, creating a damaging cycle (Rogers and Farris, 2022). Research indicates that chronic pain and mental health share the same neuronal mechanisms, making individuals with chronic pain more vulnerable to mental health disorders, and vice versa. This can often lead to harmful coping strategies, such as smoking or alcohol use for pain management (Battaglia et al., 2023).

Chronic pain can be a difficult diagnosis due to its diverse symptoms and causes. Patient history, pain intensity, location, and the daily impact of the pain are crucial for identifying the cause and choosing effective pain management. Failure to diagnose chronic pain may lead to further significant health conditions, so it is crucial to ask your doctor for help and advice to diagnose, manage, and treat chronic pain conditions. (Rahman et al., 2023). For more information, read here: How to get NHS help for your pain - NHS .

Advancements in Pain Management

Non-pharmacological approaches and interventions are often the first-line treatment for chronic, neuropathic and idiopathic pain. These include psychological interventions, including cognitive behavioural therapy, emotion-focused therapy, and support. Physical practices include exercise, yoga, physiotherapy, massage, acupuncture, and self-management practices (Wang et al., 2025).

Recent years in clinical practice have seen advancements in the techniques and medications used for neuromodulation (alteration of pain signalling throughout the body), which range in invasiveness (Krishna and Fasano, 2024). These therapies focus on the deep brain, motor cortex, and peripheral nerve activity by electrical, pharmaceutical, magnetic, or deep current stimulation directly to the nerves. (Knotkova et al., 2021).  Sensory re-education and desensitisation can reduce hypersensitivity, aiming to reduce pain (Siwy, Orroth and Novak, 2024). A key example of desensitisation is Transcutaneous Electrical Nerve Stimulation (TENS), which delivers low-voltage electrical impulses through the sensitive area of skin for pain relief by blocking pain signals from reaching the brain, further preventing the stimulation of endorphin release. These are only suitable for use if recommended by your doctor, and more information on TENS devices is available at: TENS (transcutaneous electrical nerve stimulation) - NHS .

However, excessive nerve stimulation can cause neurodegeneration and nerve damage , and increased sensitivity. Physically damaged neurons cannot regenerate, which may then require pharmacological, physiological, or surgical interventions for effective pain management, including cases in which the pain is caused by an underlying cause such as a disease or physical damage (Yang and Chang, 2019).

Pharmacological strategies and pain management medications vary in effectiveness among individuals. Analgesics, also known as pain-relieving drugs, include acetaminophen (paracetamol), NSAIDs such as ibuprofen and naproxen, antidepressants, antiepileptics, local anaesthetics, and opioids (Guven Kose et al., 2023). While these medications are safe and often effective when used appropriately, they may cause adverse effects, including the risk of addiction and misuse (Alorfi, 2023). A physician will quantify the appropriate dosage and form of medication based on the patient's medical history and symptoms (Queremel Milani and Davis, 2023). Recent studies have shown that the placebo effect, which involves treatments without active ingredients, can influence physiological processes similarly to pain-relief medications. However, this raises several ethical concerns (Kaptchuk et al, 2020). Other medications, including synthetic drug ligands that activate or inhibit neuron receptors and alter the chemical concentrations found on neuron cell membranes. (Pan et al., 2021).

Interventional procedures vary in complexity and include techniques such as corticosteroid injections that reduce inflammation and pain in arthritic conditions (Urits et al., 2020), while prolotherapy promotes healing of loosened ligaments and tendons to aid musculoskeletal pain (Bae et al., 2021). Nerve blocking is a technique applied to specific body parts, such as the limbs, that interrupts the transmission of pain signals along nerves and stops them reaching the brain, with effects lasting from hours to months (Wiederhold et al., 2020). Alternatively, the radiofrequency ablation technique uses radio waves that destroy nerve tissue through heat, damaging the targeted area of nerves (Strand et al., 2024). Recent advancements in gene therapy to aid in treating conditions that lack effective medications have focused on targeting membrane proteins that regulate electrical excitability in primary sensory neurons in the PNS, altering pain perception (Ovsepian and Waxman, 2023).

When it comes to managing long-term conditions like chronic pain, personalised treatment plans and regular monitoring are crucial. Pain tolerance, sensitivity, and perception vary among individuals due to factors including genetics, comorbidities, lifestyle factors, and personal preferences, all contributing to how an individual responds to a treatment (Świtała et al., 2021). A personalised approach is often multidisciplinary, combining different forms of treatment, such as medication combined with physiotherapy. Regular checkups aid in tracking the progress of the treatment plan, alongside the detection of any changes needed in their plan. (Cohen, Vase and Hooten, 2021).

Although these methods aim to reduce pain, improve functioning and positively impact an individual’s quality of life, research has highlighted that they often only provide short-term chronic pain management. This demonstrates the need for further research in more permanent pain relief (Knotkova et al., 2021). Advancements in pain management are leading to improved personalised and monitored treatment strategies that improve the responsiveness for the individual. Current research aims to develop longer-lasting and more definitive treatments for chronic pain conditions.

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