Herpes zoster, colloquially known as shingles, is the reactivation (from the general area of the spinal cord) of varicella zoster virus (VZV, primary infection of which leads to chickenpox), one of the Herpesviridae group, leading to a crop of painful blisters over the area of a dermatome.
The earliest symptoms of shingles include headache, sensitivity to light, flu-like symptoms without fever, as well as itching, tingling, and extreme pain where the rash is developing. Often, pain is the first symptom. This pain can be characterized as stinging, tingling, numbing, or throbbing, and can be pronounced with quick stabs of intensity. Then 1-3 crops of red lesions develop, which gradually turn into small blisters filled with serous fluid. A general feeling of unwellness often occurs. In some cases, the rash does not form blisters, but has an appearance much like urticaria ("hives").
Shingles cannot be passed from one person to another. However, the virus that causes shingles, VZV, can be spread from a person with active shingles to a person who has never had chickenpox through direct contact with the rash. The person exposed would then develop chickenpox, not shingles. The virus is not spread through sneezing, coughing or casual contact. A person with shingles can spread the disease when the rash is in the blister-phase. Once the rash has developed crusts, the person is no longer contagious. A person is not infectious before blisters appear or with post-herpetic neuralgia (pain after the rash is gone).
Chickenpox virus can remain dormant for decades, and does so inside the ganglion near the spinal cord. As the virus is reactivated it spreads down peripheral nerve fibers and produces intense pain. The blisters therefore only affect one area of the body and do not cross the midline. They are most common on the torso, but can also appear on the face (where they are potentially hazardous to vision) or other parts of the body.
Outbreaks occur for many different reasons, most of which are a result of events which depress the immune system, such as aging, severe emotional stress, severe illness or long-term use of corticosteroids. There have been recorded cases of outbreaks occurring due to unmanaged stress or other stresses to the skin such as pinching in more sensitive areas of the skin (nipples, ears, and underarms), scratching, or biting.
The causative agent for herpes zoster is varicella zoster virus (VZV). Most people are infected with this virus as a child, as it causes chickenpox. The body eliminates the virus from the system, but it remains dormant in the ganglia adjacent to the spinal cord (called the dorsal root ganglion) or the ganglion semilunare (ganglion Gasseri) in the cranial base.
Generally, the immune system suppresses reactivation of the virus. In the elderly, whose immune response generally tends to deteriorate, as well as in those patients whose immune system is being suppressed, this process fails. (Some researchers speculate that sunburn and other, unrelated stresses that can affect the immune system may also lead to viral reactivation.) The virus starts replicating in the nerve cells, and newly formed viruses are carried down the axons to the area of skin served by that ganglion (a dermatome). Here, the virus causes local inflammation in the skin, with the formation of blisters.
The pain characteristic of herpes zoster is thought to be due to irritation of the sensory nerve fibers in which the virus reproduces.[
Stages-
1)Back or underarm pain and small rash spots appear
2)Rash (itchy for some) spreads around the body
3)More pain develops
4)Bubbles filled with fluid pop up
5)After 4-5 days pain is gone and bubbles turn dark purple and peel off
Jialat liao... Scary!!! 
