Headache, toothache, face pain, wrist pain, back pain, joint pain …… Some people think that pain is not a disease, but the pain really kills. Especially those related to nerve damage pain, the attack like fire, needles, knife, not only skin pain, or nerve pain, the wind can not blow, hands can not grasp, sometimes really let people “worse than death”, life is disrupted, and even depression and insomnia. Medically, this pain is called neuropathic pain, or “neuralgia” for short. There are many causes of neuralgia, and one very typical one is the pain in the back, limbs, head and face caused by shingles infection. So how does a small virus cause such severe pain? Let’s go back to the root cause. Many people had chickenpox when they were young, and the virus that causes chickenpox is called – varicella-zoster virus. The first infection, the skin will be chicken pox, mostly distributed in the head and neck, back, especially the waist, forming the commonly known “pan head sores”, “snake wrapped around the waist”. The first thing that happens is that the rash becomes a pimple, and then it quickly turns into a rice to pea-sized blister with a clear red halo around it, and the center of the blister is umbilical fossa-shaped. 2 to 3 days later, the blister dries up and crusts over, and it recovers after the scab is removed. (See the picture below.) The virus is not idle for a moment during this process. In addition to the chickenpox-zoster virus, which likes to erode the epidermal cells of the skin to cause chickenpox, it also particularly likes to erode the nerves. It will sneak into the sensory nerve endings of the skin and move along the nerve fibers, towards the posterior root ganglion of the spinal cord, where it eventually settles (see below). Although chickenpox clears up on its own within 2-4 weeks, this virus lurks at the nerve roots of the body, mostly in the dorsal root ganglion, trigeminal ganglion, and other areas. When the body’s immunity decreases, such as poor resistance of the elderly, tumor patients after radiotherapy, or fatigue and other factors, the virus will take advantage of the opportunity to resurface, multiply in the nerve roots, sweeping the nerve cells as raw material for replication, resulting in nerve inflammation, damage or even necrosis, resulting in neuralgia; at the same time, the virus multiplies, and then moves along the nerve fibers to the skin again, thus reappearing. This leads to the reappearance of chickenpox. This patient often feels pain on the body first and is not particularly concerned, and then starts to develop herpes about 1 week later. Most people get the varicella-zoster virus when they are young, but it does not mean that everyone will develop neuralgia later. Only when the resistance decreases and the virus takes advantage of the opportunity to multiply in large numbers will it cause neuralgia and chickenpox again. If the immune system has been relatively good, even though herpes zoster is latent in the nerve roots for life, the nerves will be slightly inflamed, but it does not trigger neuralgia. Therefore, the older the patient (especially older people over 50 years old) and the lower the immunity, the more intense and longer the pain caused by shingles. Of course, this nerve damage does not mean that the nerve is cut off directly with a knife, but that the virus slowly “eats” the nerve fibers, just like a silkworm eats mulberry leaves one by one. If the virus is prevented from eating the nerve fibers, the nerve will be protected from damage; if the nerve is always in pain and unwilling to go to the hospital for treatment, the nerve may be irreversibly damaged, making treatment more difficult and the disease more likely to recur. Another condition is that if you are acutely infected with the varicella-zoster virus in adulthood, you may also experience persistent boiling water or charcoal burning-like pain in the original rash area of your body. The skin feels mildly numb and cannot be touched in any way, and even a breeze can trigger a catastrophic and severe pain, like a burst of lightning-like or tearing pain, which comes on intermittently, without knowing when an attack will occur, often lasting more than 1 month. This condition will come out as a herpes first, before the neuralgia.