Shingles

Shingles (herpes zoster) is a viral infection that causes a painful, blistering rash, caused by the same virus responsible for chickenpox — the varicella-zoster virus (VZV). Anyone who has previously had chickenpox, even decades earlier, carries this virus in a dormant state within their nervous system for the rest of their life, and shingles occurs when that dormant virus reactivates.

Shingles is not usually life-threatening, but it can be intensely painful, and in some people, the pain can persist for months or even years after the rash itself has healed — a complication called postherpetic neuralgia, described in more detail below. The good news is that shingles is both preventable, through vaccination, and treatable, particularly when antiviral medication is started early. Understanding how the virus behaves in the body helps explain why timing matters so much in shingles care.

How Shingles Actually Develops: From Chickenpox to Reactivation

After a chickenpox infection resolves, the varicella-zoster virus does not leave the body. Instead, it travels along nerve fibres and becomes dormant within clusters of nerve cell bodies near the spinal cord and brain, called dorsal root ganglia and cranial nerve ganglia, where it is normally kept in check by the immune system for years or decades without causing any symptoms.

Shingles develops when this immune control weakens — often due to ageing, illness, stress, or medication that suppresses the immune system — allowing the dormant virus to reactivate. Once reactivated, the virus travels back down the specific nerve fibre it was dormant in, toward the area of skin that nerve supplies (called a dermatome), causing local nerve inflammation and the characteristic band-like rash. This is why shingles almost always appears as a rash confined to one side of the body, following the path of a single nerve, rather than appearing symmetrically or in a scattered pattern like chickenpox.

Because the virus is travelling along and irritating a nerve, pain, burning or tingling in the affected area often begins one to five days before the rash itself appears — an important detail, since this pre-rash pain is easy to mistake for another cause until the rash makes the diagnosis clear.

Symptoms of Shingles

Shingles typically progresses through a recognisable sequence, usually affecting a single, confined area on one side of the body corresponding to the nerve involved.

• Burning, tingling, itching or stabbing pain, often the very first symptom, typically appearing several days before any visible rash
• Skin sensitivity or heightened sensitivity to touch (allodynia) in the affected area, sometimes severe enough that light contact with clothing is painful
• A red rash that develops a few days after the pain begins, usually in a band or stripe confined to one side of the body — most classically wrapping around one side of the torso, though it can appear on the face, neck, or limbs depending on which nerve is involved
• Fluid-filled blisters that develop within the rash, which typically crust over within seven to ten days and fully clear within two to four weeks
• Itching, alongside the burning pain
• Fever, headache and fatigue, particularly in the days around rash onset, reflecting the body's broader immune response to viral reactivation

It is possible to experience the characteristic nerve pain of shingles without ever developing a visible rash — a presentation sometimes called "zoster sine herpete" — which can make diagnosis more challenging and is one of several reasons unexplained, one-sided burning pain is worth having assessed.

Why Location Matters: Special Presentations Requiring Urgent Care

Because shingles follows the path of a specific nerve, where it appears on the body has real clinical significance — certain locations carry a meaningfully higher risk of serious complications and warrant urgent, rather than routine, medical attention.

Shingles Near the Eye (Herpes Zoster Ophthalmicus)
When shingles affects the nerve supplying the forehead, eyelid and tip of the nose, the virus can also affect the eye itself, risking corneal damage, inflammation inside the eye, and permanent vision loss if not treated urgently. A rash appearing on the tip, side or root of the nose (Hutchinson's sign) is a particularly strong warning sign of eye involvement. Anyone with a shingles rash near the eye should be assessed urgently, ideally by an eye specialist, even before blisters fully develop.

Shingles Affecting the Ear (Ramsay Hunt Syndrome)
When shingles reactivates in the nerve supplying the ear and face, it can cause ear pain, a rash in or around the ear canal, facial weakness or paralysis on the affected side, and hearing or balance problems. Prompt antiviral treatment gives the best chance of recovering facial nerve function, so this presentation also warrants urgent assessment rather than routine scheduling.

In people with significantly weakened immune systems, the virus can occasionally spread beyond the original nerve to cause a widespread rash resembling chickenpox across the body, sometimes with involvement of internal organs — a condition called disseminated zoster, which requires hospital-based treatment.

What Causes Shingles

Shingles has a single underlying cause — reactivation of the varicella-zoster virus in someone who has previously had chickenpox — but several factors influence why and when that reactivation happens.

• Age-related decline in immune function: The most significant factor. As the immune system's ability to keep the dormant virus suppressed gradually declines with age (a process called immunosenescence), the likelihood of reactivation rises substantially, particularly from the 50s onward.
• Weakened immunity from illness or its treatment: Conditions such as HIV/AIDS, certain cancers (particularly blood cancers), and treatments such as chemotherapy or radiotherapy weaken the immune system's ability to keep the virus dormant.
• Immunosuppressive medication: Medications used to prevent organ transplant rejection, and long-term or high-dose corticosteroid use, suppress immune function and increase the likelihood of viral reactivation.
• Physical or emotional stress and illness: Periods of significant physical or emotional stress, and other illnesses, have been associated with shingles episodes in some individuals, thought to be related to temporary dips in immune function, although the relationship is not fully understood.

Because reactivation depends on prior chickenpox infection, anyone who has had chickenpox carries a lifelong risk of developing shingles — and in regions where chickenpox vaccination is not universal, this includes the large majority of adults.

Is Shingles Contagious?

Shingles itself cannot be passed from one person to another in the way a typical infection spreads. However, the fluid within shingles blisters does contain live varicella-zoster virus, and direct contact with this fluid can transmit the virus to someone who has never had chickenpox or the chickenpox vaccine — in that person, it would cause chickenpox, not shingles.

• Anyone who has not had chickenpox or the chickenpox vaccine, including most infants
• Pregnant women who are not immune to chickenpox, given the risk chickenpox infection poses to the pregnancy
• People with weakened immune systems, for whom even a mild infection can become more serious

The risk of transmission is present only through direct contact with fluid from open blisters, and only until the blisters have fully crusted over — shingles is not spread through coughing, sneezing or casual contact the way chickenpox itself can be. Keeping the rash covered and avoiding contact with the groups above until blisters have crusted meaningfully reduces this risk.

Risk Factors for Shingles

• Age: Risk rises significantly with age, and shingles is substantially more common in adults over 50, reflecting the natural, gradual decline in the immune system's ability to keep the virus suppressed.
• Being immunocompromised: Conditions that weaken the immune system, such as HIV/AIDS or certain cancers, meaningfully increase the risk of shingles at any age.
• Cancer treatments: Chemotherapy or radiotherapy can lower the body's resistance to viral reactivation during and after treatment.
• Certain medications: Drugs that prevent rejection of transplanted organs, or long-term use of steroids, increase the risk of shingles by suppressing normal immune surveillance.
• Previous episode of shingles: A first episode of shingles does not confer lasting immunity — a second or even third episode is possible, particularly in those who remain immunocompromised or are of advancing age.
• Family history: A family history of shingles has been associated with a modestly higher personal risk in some studies, suggesting a possible genetic contribution to how well the virus is kept suppressed.

Complications of Shingles

Most people recover from shingles without lasting effects, but a number of complications can occur, particularly if treatment is delayed or the immune system is significantly weakened.

• Postherpetic neuralgia (PHN): The most common complication, occurring when nerve fibres damaged by the virus continue to send incorrect pain signals to the brain even after the rash has healed. Pain can range from mild to severe and, in some cases, persists for months or years, significantly affecting sleep, mood and quality of life. Risk increases with age and with more severe initial pain or rash.
• Vision loss: Shingles affecting the eye can cause painful eye infection, corneal scarring, and in serious cases, permanent vision loss if not treated urgently, as described above.
• Neurological problems: Shingles can, in rare cases, lead to encephalitis (inflammation of the brain), facial paralysis, or problems with hearing or balance, particularly with involvement of the facial or auditory nerves as seen in Ramsay Hunt syndrome.
• Skin infections: Blisters that are scratched, or not kept clean, can become infected with bacteria, occasionally requiring antibiotic treatment and, in rare cases, causing scarring.
• Disseminated (widespread) zoster: In people with significantly weakened immune systems, the virus can spread beyond the original nerve and, rarely, involve internal organs such as the lungs or liver, requiring hospital-based intravenous treatment.

How Shingles Is Diagnosed

Shingles is usually diagnosed clinically, based on the characteristic appearance and one-sided, band-like distribution of the rash, though additional testing may be used in less typical or more complex cases.

• Clinical Examination: In most cases, the distinctive appearance and dermatomal (single nerve band) distribution of the rash is sufficient for a doctor to diagnose shingles without further testing.
• Viral PCR Testing: A swab of fluid from a blister can be tested to confirm the presence of varicella-zoster virus, useful when the diagnosis is uncertain, in atypical presentations, or in immunocompromised patients where confirming the exact cause matters for treatment planning.
• Eye Examination: Recommended whenever shingles affects the area around the eye, to check for corneal involvement or internal eye inflammation that may not be visible without specialised examination equipment.
• Blood Tests: Not usually needed to diagnose typical shingles, but may be used to investigate an underlying cause of immune suppression in patients who develop shingles at a younger age than expected or experience recurrent episodes.

Preventing Shingles: Vaccination

The most effective way to reduce the risk of developing shingles, and its complications, is vaccination — a significant advance in shingles prevention over the past decade.

• Shingrix (recombinant zoster vaccine): A non-live, recombinant vaccine given as two doses, two to six months apart, that has shown effectiveness above 90% in preventing shingles in clinical studies, with protection that appears to remain strong for at least several years after vaccination. It is the vaccine generally recommended in Singapore and many other countries today, having largely superseded the older live-attenuated Zostavax vaccine, which had lower and less durable efficacy, particularly in older adults.
• Who should be vaccinated: Shingrix is generally recommended for all adults aged 50 and above, regardless of whether they recall having had chickenpox or a previous episode of shingles, as well as for adults aged 18 and above with weakened immune systems, who face a higher risk of shingles and its complications.
• Vaccination in immunocompromised individuals: Because Shingrix is a non-live vaccine, it is generally considered suitable for people who are immunocompromised, unlike the older live-virus vaccine, though the specific timing and suitability should always be discussed with a doctor given individual circumstances.
• Preventing chickenpox itself: For those who have never had chickenpox, the varicella (chickenpox) vaccine prevents the initial infection and, by extension, the possibility of shingles later in life, since shingles cannot occur without prior varicella-zoster infection.

Vaccination remains worthwhile even after a previous episode of shingles, as it reduces the risk of future episodes and is generally recommended once the acute illness has resolved.