I. How Does the Virus "Attack" the Nerves?

1. From latency to reactivation: the virus's "route of march"
To understand postherpetic neuralgia (PHN), we must first understand the "attack path" of the varicella‑zoster virus.

After a person contracts chickenpox, the virus travels along sensory nerves into the spinal ganglia or cranial sensory ganglia, where it establishes long‑term latency. When immune function declines, the latent virus reactivates, replicates extensively, and spreads along sensory nerve fibres to the corresponding dermatomes.

In this process, the virus not only causes skin blisters but, more critically, inflicts substantial damage on sensory ganglia and nerve fibres. Affected neurons undergo inflammation, haemorrhage, and even necrosis. The consequence of this damage is neuronal dysfunction and ectopic discharge, ultimately leading to pain.

In every adult, the varicella‑zoster virus lies dormant in two main sites: the trigeminal ganglion and the dorsal root ganglia alongside the spinal cord. This is why shingles most commonly appears on the head and face (trigeminal territory) and on the chest and back (spinal nerve territory).

2. The "domino effect" of nerve damage
The varicella‑zoster virus is neurotropic—it has a particular affinity for attacking nerve tissue. After reactivation, the virus replicates vigorously within the ganglia and adjacent cells. The resulting inflammation causes local nerve damage, including demyelination, axonal degeneration, and necrosis of sensory nerve fibres and surrounding cells.

Think of a nerve as an electrical wire—the myelin sheath is the insulating layer, and the axon is the conductive metal core. The viral attack causes the "insulation" to peel off, leaving the nerve "exposed." These exposed nerves become hypersensitive, and even mild stimuli can trigger abnormally intense discharges.

II. Peripheral Sensitisation and Central Sensitisation: The Dual Mechanisms That "Amplify" Pain

The exact mechanisms underlying PHN are not yet fully understood, but research indicates that they are closely related to neural plasticity. In simple terms, the nervous system undergoes "adaptive changes" after injury—but these changes are detrimental, as they continuously amplify pain signals. Current research focuses on two core mechanisms: peripheral sensitisation and central sensitisation.

1. Peripheral sensitisation: nerve endings become "over‑reactive"
Peripheral sensitisation refers to neurochemical, physiological, and anatomical changes in primary sensory neurons following nerve injury. These changes sensitise peripheral nociceptors and amplify the incoming neural signals.

Put simply: normal nerve endings send pain signals to the brain only when stimulated strongly enough. But damaged nerve endings become abnormally sensitive—light touch, temperature changes, or even no stimulus at all can trigger intense pain signals.

Specific manifestations of peripheral sensitisation include:

• Ion channel abnormalities: upregulation of sodium and calcium channels increases neuronal excitability.

• Neuroinflammation: viral infection triggers local inflammation and release of pro‑inflammatory cytokines, exacerbating nerve damage.

• Nerve fibre degeneration: damage to Aβ fibres (which convey touch) and C fibres (which convey pain) leads to abnormal sensory input.

Studies have also shown that PHN patients exhibit marked loss of myelinated fibres in the sensory ganglia, ganglion defibrosis, and atrophy of the spinal dorsal horn. Such structural changes confirm that nerve damage is real and not "psychological."

2. Central sensitisation: the brain's "volume" is turned up
Central sensitisation is more complex and harder to manage than peripheral sensitisation. It refers to abnormally increased excitability or enhanced synaptic transmission of pain‑related neurons at the spinal cord level and above, thereby amplifying pain signal transmission.

Pathophysiological changes in central sensitisation include: upregulation of voltage‑gated calcium and sodium channels, reduced function of inhibitory neurons, and necrosis of supporting cells.

An analogy: peripheral sensitisation is like a microphone becoming too sensitive, while central sensitisation is like turning up the amplifier's volume. When both occur, even a faint original stimulus becomes a deafening signal reaching the brain.

Central sensitisation is the main mechanism underlying the persistent pain of PHN. This means that even if peripheral nerve damage partially repairs, the central nervous system may have "learned" the pain, and pain signals continue to be emitted.

3. Inflammation and deafferentation: two additional "accomplices"
Besides peripheral and central sensitisation, two other mechanisms play important roles in PHN:

• Inflammatory response: reactivation of the varicella‑zoster virus increases peripheral nerve excitability and sensitivity through secondary inflammation.

• Deafferentation: extensive degeneration and necrosis of primary afferent fibres lead to deafferentation of central neurons, which in turn causes secondary increases in central neuronal excitability.

These four mechanisms—peripheral sensitisation, central sensitisation, inflammation, and deafferentation—often coexist and reinforce each other, together forming the complex pathological foundation of PHN.

III. From Acute Pain to Chronic Pain: An "Irreversible" Turning Point

1. Why does pain "never stop" in some people?
Not all shingles patients progress to PHN. The key distinction lies in whether timely intervention occurs during the peripheral sensitisation phase.

If effective intervention is not provided in a timely manner during peripheral sensitisation, permanent pathological changes may ensue, greatly increasing the risk of PHN. Neuroinflammation, epigenetic regulation, and psychosocial factors jointly drive the transition from acute to chronic pain.

This is why the 72‑hour "golden window" in the acute phase of shingles is so crucial. Early intervention when the virus has just reactivated and nerve damage is still in its early stages may prevent or alleviate subsequent chronic pain.

2. Differences in pain mechanisms among patient subtypes
Notably, pain mechanisms may differ among patients:

• "Irritable nociceptor" type: characterised by preserved sensation but prominent allodynia.

• "Deafferentation" type: characterised by marked sensory loss.

These differences directly affect treatment choices. A therapy that works for one type may be less effective for another. This is why PHN treatment requires individualised approaches.

IV. From Pathology to Clinical Presentation: How Mechanisms Shape Symptoms

Understanding the pathology explains the typical symptoms of PHN:

• Spontaneous pain: increased spontaneous neuronal firing, causing pain even without any stimulus.

• Hyperalgesia: an exaggerated or prolonged response to noxious stimuli.

• Allodynia: pain triggered by normally non‑noxious stimuli (e.g., light touch, a breeze).

Among these, allodynia is one of the most tormenting features—combing hair, washing the face, wearing a mask, friction from a pillow, or even a gentle breeze can evoke stabbing or burning agony.

These symptoms are not "fanciful" or "psychological"—they are tangible dysfunctions of the nervous system. Understanding this is essential for patients and their families to correctly recognise the condition and actively seek appropriate treatment.

Qingdao Tiantian Traditional Chinese Medicine Clinic’s Five‑linked Anti‑drug Pain Therapy is a comprehensive external treatment approach using traditional Chinese medicine, specifically designed for shingles and postherpetic neuralgia. It offers a professional TCM‑based external option for patients suffering from head‑and‑face shingles and related neuralgia. If you or your loved ones are troubled by such pain, we recommend consulting a licensed medical institution for evaluation and treatment under the guidance of qualified practitioners.

The therapeutic rationale is "toxin‑removal and pain‑relief"—that is, through specialised techniques, it aims to clear the "viral toxins" retained in the deep layers of the skin that persistently stimulate nerves, thereby facilitating nerve repair and alleviating pain. The entire procedure is performed by qualified medical staff in a professional healthcare setting.

Indications
This therapy is mainly applicable to the following conditions:

• Herpes zoster (shingles)

• Postherpetic neuralgia

• Postherpetic neuralgia without rash (zoster sine herpete)

• Trigeminal neuralgia

For shingles‑associated PHN occurring on the head and face, the therapy also provides corresponding treatment protocols. Based on extensive clinical experience, for most patients without serious underlying diseases and who strictly adhere to the contraindication instructions along with their families, significant improvement or gradual pain resolution is generally observed within 3 to 8 sessions. Treatment outcomes vary from person to person and are influenced by individual differences, disease duration, underlying health conditions, and other factors.


Disclaimer:
This content is a summary of clinical experience and observations from TianDao Traditional Chinese Medicine over many years. It is intended for patient education, public awareness, and scientific exchange. It does not constitute a guarantee of cure, safety, or efficacy for any condition, nor is it a promotional promise.