Understanding Pain: Mechanisms and Types

Introduction

Pain is one of the most common reasons for seeking care in both conventional medicine and complementary therapies. Yet it remains poorly understood by the general public and sometimes even by healthcare professionals. The International Association for the Study of Pain (IASP) defined it in 2020 as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage." This definition highlights a fundamental point: pain is not purely physical. It always includes emotional, cognitive and social dimensions.

Approximately 20% of the European population suffers from chronic pain, according to Breivik et al. (2006). Understanding pain mechanisms is the first step toward appropriate care.

Nociception: The Alarm Signal

Nociception refers to the neurophysiological process by which the body detects potentially harmful stimuli. This process unfolds in four stages:

• Transduction: nociceptors (free nerve endings located in skin, muscles, viscera and joints) convert mechanical, thermal or chemical stimuli into electrical signals. Myelinated A-delta fibers transmit sharp, localized pain. Unmyelinated C fibers carry dull, diffuse pain.
• Transmission: the electrical signal travels through peripheral nerves to the dorsal horn of the spinal cord for its first synaptic relay. From there, ascending pathways (spinothalamic tract) carry information to the thalamus and then the cerebral cortex.
• Perception: at the cortical level, the signal becomes conscious and acquires its sensory dimension (location, intensity) and emotional dimension (unpleasantness, fear). The somatosensory cortex, anterior cingulate cortex and insula are the primary regions involved.
• Modulation: the nervous system has inhibitory mechanisms descending from the brainstem (periaqueductal gray matter, raphe nuclei) that release endorphins, serotonin and noradrenaline to attenuate pain signals. This is the system engaged by acupuncture, hypnosis and physical exercise.

Types of Pain

Acute Pain

Acute pain is a physiological alarm signal. It occurs in response to an identifiable injury (fracture, burn, infection) and resolves with healing. Its duration is generally less than three months. It plays a protective role by prompting the individual to remove the affected area from danger and rest to allow tissue repair.

Chronic Pain

When pain persists beyond three months — or beyond the normal healing time — it is classified as chronic. It loses its protective function and becomes a condition in its own right. The WHO's International Classification of Diseases (ICD-11) now dedicates a specific chapter to it. Chronic pain is often accompanied by fatigue, sleep disturbances, anxiety and depression, forming a vicious cycle.

Nociceptive Pain

This results from nociceptor activation by actual tissue injury or inflammation. Examples: osteoarthritis, tendinitis, colic, post-surgical pain. It generally responds well to anti-inflammatory drugs and manual approaches (osteopathy, massage).

Neuropathic Pain

This is caused by injury or dysfunction of the nervous system itself. Patients describe burning sensations, electric shocks, tingling or numbness. Examples: trigeminal neuralgia, diabetic neuropathy, post-herpetic neuralgia, carpal tunnel syndrome. It responds poorly to standard analgesics but may benefit from acupuncture, neurostimulation or hypnosis.

Nociplastic Pain

A recent concept introduced by IASP, nociplastic pain occurs without identifiable tissue or nerve damage. It results from altered pain processing by the central nervous system — known as central sensitization. Fibromyalgia, irritable bowel syndrome and certain tension headaches are examples. Mind-body approaches (hypnosis, sophrology, meditation) show particular effectiveness for this type.

Gate Control Theory

Proposed by Melzack and Wall in 1965, this theory revolutionized pain understanding. It posits that a "gate" mechanism in the dorsal horn of the spinal cord modulates the passage of pain messages to the brain. Large-diameter sensory fibers (touch, pressure) can "close the gate" and block pain transmission. This principle explains the relief obtained by rubbing a painful area, and is also the theoretical foundation for transcutaneous electrical nerve stimulation (TENS), acupuncture and certain manual techniques.

The Biopsychosocial Model

Since the work of George Engel (1977), the scientific community recognizes that pain cannot be reduced to its biological dimension alone. The biopsychosocial model integrates three dimensions:

• Biological: tissue injury, inflammation, nerve dysfunction, genetic predispositions.
• Psychological: anxiety, depression, catastrophizing, helplessness, past painful experiences, beliefs about pain.
• Social: isolation, financial hardship, job dissatisfaction, medico-legal issues, family support.

This model justifies the multidisciplinary and integrative approach to pain, combining medical treatments, body-based approaches and psycho-emotional support.

Neuroplasticity and Pain Memory

The nervous system is not fixed. Under the effect of repeated or prolonged painful stimulation, dorsal horn neurons become hyperexcitable — this is central sensitization. Pain thresholds decrease (hyperalgesia), and normally painless stimuli become painful (allodynia). The brain itself reorganizes: functional imaging shows changes in activity and structure of pain-processing regions.

The good news is that this plasticity works in both directions. Approaches such as mindfulness meditation, hypnosis, cognitive behavioral therapy and graded physical exercise can "reprogram" these circuits and reduce central sensitization. This provides strong support for integrative approaches.

Pain Assessment

Since pain is subjective, its assessment relies on validated tools:

• Visual Analog Scale (VAS): a 10 cm line on which the patient indicates pain intensity.
• Numerical Rating Scale (NRS): the patient assigns a score from 0 to 10.
• DN4 Questionnaire: screening tool for neuropathic pain (4 questions, 10 items).
• Brief Pain Inventory (BPI): evaluates pain intensity and its impact on daily activities.
• McGill Pain Questionnaire (MPQ): explores the sensory and affective dimensions of pain.

Integrative Pain Approaches

Pain treatment is not limited to medication. Current guidelines recommend multimodal care combining:

• Manual approaches: osteopathy, chiropractic, therapeutic massage.
• Acupuncture: stimulation of descending inhibitory pathways and endorphin release.
• Mind-body approaches: hypnosis, sophrology, meditation, yoga, tai chi.
• Herbal medicine: devil's claw, turmeric, willow bark, capsaicin.
• Adapted physical activity: recognized as the most effective non-pharmacological treatment for chronic pain.
• Therapeutic education: understanding pain to manage it better (pain neuroscience education).

Disclaimer

This article is provided for informational and educational purposes only. It does not replace professional medical advice. Any persistent or unusual pain should be evaluated by a qualified healthcare professional. The complementary approaches mentioned are not substitutes for conventional medical treatments.