Quick answer. Cold sores are small, painful blisters around the lips or mouth caused by the herpes simplex virus, usually type 1 (HSV-1). They are very common: most people are exposed to HSV-1 at some point. After the first infection the virus stays dormant and can reactivate, triggered by sunlight, stress, illness, fever or tiredness. There is no cure, but cold sores are manageable – antiviral creams or tablets (such as aciclovir) work best when started at the very first tingle, before the blister forms. They are contagious, so avoid kissing and sharing cups or lip products during an outbreak. Oral herpes (HSV-1) is not the same as genital herpes (usually HSV-2). See a doctor if outbreaks are frequent, severe, near the eyes, or you have weak immunity.
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Cold sores are small, fluid-filled blisters that appear around the lips and mouth. They are caused by the herpes simplex virus (HSV), usually type 1 (HSV-1), and they are extremely common – a large proportion of adults carry HSV-1, often picked up in childhood through ordinary contact such as a kiss from a relative.
Once you have the virus it stays in your body for life, lying dormant in the nerves and reactivating from time to time to cause an outbreak. There is no cure, but the good news is that cold sores are very manageable, and antiviral treatment works best if you start it early. This guide explains the typical stages, common triggers, how to treat and reduce outbreaks, how to avoid passing it on, and how oral herpes differs from genital herpes.
At a glance
| Topic | Details | What to do |
|---|---|---|
| First sign (prodrome) | Tingling, itching or burning at the spot, before any blister appears | Start antiviral cream or tablets now – this is when they work best |
| Blister stage | Small painful blisters form, then burst, weep and crust over | Keep clean; avoid touching, kissing or sharing items; do not pick scabs |
| Common triggers | Strong sunlight, stress, fatigue, fever or illness, menstruation | Use lip sunscreen; manage stress and sleep where possible |
| Treatment | Antiviral creams (e.g. aciclovir) for occasional sores; antiviral tablets for more severe or frequent outbreaks | See a GP for tablets or if outbreaks are frequent |
| See a doctor | Sores near the eye, very frequent or severe outbreaks, weak immunity, not healing in ~2 weeks | Get medical assessment – antiviral tablets or further advice may help |
What cold sores are and how they progress
Cold sores (also called herpes labialis or oral herpes) are caused by the herpes simplex virus, most often HSV-1. After the very first infection – which may cause no symptoms or a more widespread mouth infection in young children – the virus travels to a nerve and stays dormant. It can then reactivate later to cause a cold sore.
A typical outbreak goes through stages over about 7-10 days:
- Tingling/itching at the spot (the prodrome), often a day before anything is visible
- Blisters – small, painful, fluid-filled spots, usually on or around the lip
- Weeping as the blisters burst
- Crusting and healing, usually without a scar
Common triggers
Once you carry the virus, certain things can prompt an outbreak. Common triggers include:
- Strong sunlight / UV exposure – a frequent trigger in sunny Singapore
- Stress and tiredness
- Illness or fever (hence the old name ‘fever blisters’)
- Hormonal changes, such as around menstruation
- A temporarily weakened immune system
Knowing your triggers can help you reduce outbreaks – for example, using a lip balm with sunscreen and protecting your face from strong sun.
Treatment – antivirals work best early
There is no cure for HSV, but cold sores can be treated and outbreaks shortened, especially if you act quickly. Antiviral treatment works best when started at the very first tingle, before the blister fully forms:
- Antiviral creams (such as aciclovir) – available at pharmacies; most useful when applied at the first sign and used as directed.
- Antiviral tablets (such as aciclovir, valaciclovir or famciclovir) – prescribed by a doctor for more severe, frequent or troublesome outbreaks, and most effective when started early.
- Comfort measures – keep the area clean, use lip balm to ease cracking, and take paracetamol for pain if needed.
For people who get very frequent outbreaks, a doctor may discuss taking antiviral tablets regularly to suppress them. Avoid touching the sore, and never rub the fluid towards your eyes.
Cold sores are contagious – how to avoid passing them on
Cold sores are most contagious when blisters are present and weeping, but the virus can spread even between outbreaks. To protect others, especially during an outbreak:
- Avoid kissing, and do not kiss babies or young children when you have an active cold sore.
- Do not share cups, cutlery, towels, lip balm or lipstick.
- Wash your hands after touching the sore, and avoid touching your eyes or genitals.
- Avoid oral sex during an outbreak, as HSV-1 can be passed to a partner’s genitals.
Take extra care around newborns and anyone with a weakened immune system, in whom HSV can occasionally cause more serious infection.
Cold sores vs genital herpes, and when to see a doctor
Cold sores around the mouth are usually caused by HSV-1, while genital herpes is more commonly caused by HSV-2 – they are not the same condition, though both are herpes simplex viruses. HSV-1 can sometimes be passed to the genitals through oral sex, and the two are managed differently; for genital symptoms, see our separate guidance and a doctor. Having cold sores does not mean you have a sexually transmitted infection.
See a doctor (a GP, polyclinic or skin specialist) in Singapore if:
- Cold sores are frequent, severe or very painful
- A sore is near or affecting the eye, or your vision changes – this needs prompt attention
- The outbreak is not healing within about two weeks
- You have a weakened immune system or the infection is widespread
- You are unsure whether it is a cold sore or something else
Related guides
- Best Dermatology Clinics in Singapore — our editorial shortlist
- dermatology clinics directory
- Cellulitis
- Boils & abscesses
- Scabies
Sources
- HealthHub (Singapore) – Genital Herpes (HSV-1 vs HSV-2)
- World Health Organization – Herpes simplex virus
- Johns Hopkins Medicine – Oral Herpes
- National University Hospital (NUH) – Skin Infections
Related conditions & guides
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- Fungal Nail Infection (Onychomycosis) in Singapore
- Fungal Skin Infections in Singapore
- Viral Warts Treatment in Singapore
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