Cold Sores (Herpes Labialis): Causes, Triggers and Care

Cold sores are small, painful, fluid filled blisters on or around the lips caused by the herpes simplex virus, usually type 1 (HSV-1). They typically begin with tingling or burning, form blisters within about two days, then crust and heal within 10 days to two weeks, but the virus stays in the body and can flare again with triggers like fever, strong sun, stress or periods.

In India, cold sores are often called fever blisters or simply dismissed as heat. They are very common and usually harmless in healthy adults, but they spread easily and can be serious for newborns and people with eczema or weak immunity. This guide explains what to expect and how to protect the people around you.

What causes cold sores?

Cold sores are caused by the herpes simplex virus. The World Health Organization estimates that about 3.8 billion people under the age of 50, or 64% of the world’s population, have HSV-1 infection, and most of these infections are picked up in childhood.

The American Academy of Dermatology notes that cold sores are so contagious that many people catch the virus by the age of 5, often from a kiss or shared utensils. After the first infection, the virus stays dormant (asleep) in nerve cells for life. Many people never get symptoms, while others get repeated cold sores in the same spot.

Having cold sores is common and is not a sign of poor hygiene.

What are the stages of a cold sore?

The NHS describes a typical pattern:

Stage	What happens
Tingling	Tingling, itching or burning on the lip a day or so before anything is visible
Blisters	Small, fluid filled blisters appear, usually within 48 hours
Bursting	Blisters burst and leave shallow, sore patches
Crusting	The sores dry and form scabs
Healing	The scabs fall off and the skin heals, usually within 10 days

The first ever infection, especially in children, can be more intense, with sores inside the mouth, swollen gums, fever and difficulty eating or drinking.

What triggers a cold sore?

The NHS lists common triggers:

• Illness, such as a cold, flu or fever
• Sunshine, including strong summer sun and sun reflected off snow or water
• Periods

Many people also notice cold sores after tiredness, stress, dental treatment or injury to the lips. Keeping track of your own triggers can help you plan.

How can I stop cold sores from spreading?

The NHS says you are contagious from the moment you first feel tingling until the sore has completely healed. The AAD adds that you can still spread the virus even while using treatment. To protect others and the rest of your body:

• Do not kiss anyone, and never kiss babies or young children
• Avoid oral sex until the sore has fully healed
• Do not share lip balm, lipstick, cups, spoons, straws, towels or razors
• Do not touch the sore except to apply treatment, and wash your hands afterwards
• Avoid touching your eyes after touching the sore
• Keep away from newborns, people with eczema and anyone with weak immunity, as the AAD advises

In Indian families, where babies are often passed around and kissed by many relatives, it is worth gently telling family members to wait until a cold sore heals.

What can I do at home for a cold sore?

Based on NHS advice:

1. Start treatment early. Antiviral creams from a pharmacy work best when started at the tingling stage. Dab the cream on, do not rub
2. Take paracetamol or ibuprofen for pain or swelling if needed, following the pack instructions
3. Drink plenty of fluids
4. Avoid acidic or salty foods if they sting
5. Use a lip balm with SPF 15 or more outdoors to reduce sun triggered flares
6. Leave the scab alone. Picking can delay healing and spread the virus

Avoid steroid creams on a cold sore, as well as toothpaste, alcohol, lemon or other home remedies that can irritate broken skin.

How does a dermatologist treat cold sores?

The American Academy of Dermatology (AAD) says many cold sores go away without treatment in 7 to 14 days, but some people need medical care. Dermatologists recommend seeing a doctor if you have a cold sore near an eye, several cold sores or a lot of pain, or if your immune system is weakened by illness or medicines such as chemotherapy.

A dermatologist can often diagnose a cold sore just by looking at it, and may take a swab to confirm the virus. Treatment may include:

• Antiviral medicine, as a cream or tablets, chosen to suit your situation. The AAD notes that starting treatment before the sore appears, or as soon as you notice it, can reduce discomfort and speed healing
• Daily antiviral medicine for some people who get frequent cold sores, to reduce the number of outbreaks
• A broad spectrum lip balm with SPF 30 or higher, used year round if sun triggers your cold sores

Two practical tips from the AAD:

• Dab cream on with a clean cotton bud rather than your finger, so the virus does not get onto the tube
• Throw away lip balm and lipstick you used during a cold sore once it has cleared, as these can carry the virus and cause another sore

Is it a cold sore or something else?

Other conditions around the mouth can be confused with cold sores:

• Mouth ulcers, which form inside the mouth and are not caused by herpes
• Angular cheilitis, painful cracks at the corners of the mouth
• Impetigo, a bacterial infection with honey coloured crusts, common in children
• Allergic or irritant reactions to lipsticks, toothpaste or lip balm

If you are unsure, a dermatologist can usually tell the difference by examining the area.

When is a cold sore an emergency?

Most cold sores are not serious, but some situations need urgent care:

• A baby with blisters or sores, especially a newborn, or a baby who is feeding poorly, very sleepy or has a fever
• Eczema herpeticum. DermNet describes this as one of the few dermatological emergencies. It happens when herpes spreads over eczema affected skin, causing many painful, punched out sores and often fever. It is more common in infants and children with eczema. Read more in our eczema guide
• Sores near the eye, eye pain, redness or blurred vision, because HSV-1 can rarely infect the eye, as the WHO notes
• Severe headache, confusion, drowsiness or a seizure, which can rarely signal a brain infection
• Widespread sores in someone with weak immunity, such as those on chemotherapy or with poorly controlled diabetes

For a seriously unwell baby or adult, call 112 or 108 for an ambulance in India or go to the nearest emergency department. Our guide on when to see a dermatologist urgently lists other warning signs.

Are cold sores the same as shingles or chickenpox?

No, but they belong to the same family of viruses. Chickenpox and shingles are caused by the varicella zoster virus, while cold sores are caused by herpes simplex. Shingles usually forms a band of blisters on one side of the body. Our guide on chickenpox and shingles explains the difference.

You may also find this guide useful: Dry, Chapped Lips (Cheilitis): Causes and Lip Care That Works.

You may also find this guide useful: Mouth Ulcers: Causes and When to Worry.

When to see a dermatologist

See a doctor or dermatologist if:

• A cold sore has not started healing after 10 days
• The sore is unusually large, painful or spreading
• You also have swollen, painful gums and sores inside the mouth
• You get cold sores very often and they affect your work or confidence
• You have eczema, are pregnant, or have weak immunity
• You are not sure whether the sore is herpes or something else

If you get frequent cold sores and want a plan to manage them, Dr. Maria offers online consultations where you can discuss your triggers and treatment options. A baby or anyone with eye symptoms needs to be seen in person urgently.