Cold sores are common, uncomfortable and, let's be honest, pretty annoying. Knowing the cold sore stages helps you spot one early, treat it at the right time and avoid passing it on. That matters, because starting treatment at the first tingle gives you the best chance of a quicker recovery.
This guide covers what causes cold sores, what triggers them, how each stage looks and feels, and the treatments that can help, including antiviral tablets like Aciclovir and Valaciclovir.
Cold sores are very common and nothing to be embarrassed about. Most clear up on their own within about 10 days.
What causes cold sores?
Cold sores are caused by the herpes simplex virus type 1 (HSV-1). It's extremely common. Around two-thirds of people under 50 worldwide carry HSV-1, and many never get symptoms.1
The virus spreads through close contact, such as kissing, or by sharing things that touch the mouth, like cups, cutlery, lip balm and towels.2 It can sometimes spread even when there's no visible sore.1
Once you've caught it, HSV-1 stays in your body for life. It lies dormant in the nerve cells and can reactivate from time to time, usually in the same spot.2 The first outbreak tends to be the worst, and later ones are often milder.
Having the virus doesn't mean you'll get cold sores often. Some people have one outbreak and never another.
What triggers cold sores?
Something usually wakes the virus up, and the NHS lists a few common triggers.2 These include:
- Being run down or ill, for example with a cold or flu
- Stress
- Strong sunlight
- Periods
Some people also notice cold sores after a knock to the lips or when their lips get chapped in cold, windy weather. Spotting your own pattern can help you get ahead of the next one.
What are the stages of a cold sore?
Most cold sores follow the same five stages and clear up within about 10 days.2
Tingling
A day or two before anything appears, you may feel tingling, itching, burning or tightness around your lips. This is the best time to start treatment.
Blisters
Small, fluid-filled blisters pop up, usually on or around the edge of your lip. They often appear in a cluster.
Weeping
The blisters burst and leave shallow, painful sores. This is when a cold sore is at its most contagious.
Crusting
The sores dry out and form a yellowish or brown crust. It can feel itchy and may crack when you move your mouth.
Healing
The scab falls away, sometimes leaving the skin pink or slightly flaky for a few days. A cold sore stays contagious until it has completely healed.2
Do not pick or touch the scab. Fingers that touch a cold sore can carry the virus to other people or other parts of your body.
How are cold sores treated?
There's no cure for HSV-1, but treatment can help cold sores heal faster and feel less painful. Timing is everything: the earlier you start, the better.2
Antiviral creams
Antiviral creams containing aciclovir are available from pharmacies. They work best if you start using them as soon as you feel the first tingle, and you apply them several times a day for around 5 days.3
Cold sore patches can also protect the area while it heals and make it less noticeable.2
Aciclovir tablets
Aciclovir tablets are an antiviral treatment for herpes infections, including cold sores. They stop the virus multiplying, which helps the sores heal and can ease symptoms.3
You usually take them several times a day for a few days, so it helps to set reminders.
Valaciclovir tablets
Valaciclovir is what's called a pro-drug. Once you swallow it, your body converts it into aciclovir.4
The main difference is convenience. Your body absorbs more of the medicine from valaciclovir, so you need fewer doses. For cold sores, the usual course is just one day.4
Antiviral tablets are often used for severe cold sores or people who get them frequently. A prescriber can advise whether they're right for you.
If you get cold sores regularly, keep treatment at home. Starting it at the first tingle can make a real difference.
How to stop cold sores spreading
Cold sores are contagious from the first tingle until they've completely healed. There are simple ways to lower the risk of passing the virus on.2 Try to:
- Wash your hands before and after applying cream
- Avoid touching the cold sore
- Avoid kissing and oral sex until it has fully healed
- Keep your lip balm, lipstick, cups, cutlery and towels to yourself
- Keep your cold sore cream or tablets for your own use only
Take extra care to keep the virus away from your eyes. If a cold sore spreads to the eye, it can cause a more serious infection.
Do not kiss babies while you have a cold sore. The virus can make newborns seriously ill.
When should you see a GP?
Most cold sores don't need a doctor, but the NHS advises getting checked in some cases.2 See a GP if:
- Your cold sore hasn't started healing after 10 days
- It's very large or painful
- You or your child has swollen, painful gums and sores in the mouth
- You have a weakened immune system, for example because of chemotherapy or diabetes
- You're pregnant
A cold sore that's slow to heal or unusually large is worth getting checked, rather than waiting for it to clear on its own.
If a cold sore is near your eye, or your eye becomes red, painful or your vision changes, get medical advice the same day.
Frequently asked questions
How long do cold sores last?
Most cold sores clear up on their own within about 10 days. Starting antiviral treatment at the first tingle can help them heal faster. If a cold sore hasn’t started to heal after 10 days, or it’s very large or painful, speak to a GP or pharmacist.
How do you get rid of a cold sore in 24 hours?
Unfortunately, there’s no way to make a cold sore disappear overnight. The best thing you can do is start antiviral treatment as soon as you feel the first tingle, which can help it heal faster. Cold sore patches can also cover it and make it less noticeable while it heals.
Are cold sores contagious?
Yes. Cold sores are contagious from the first tingle until they’ve completely healed, and they’re most contagious when the blisters burst. The virus spreads through close contact like kissing, or by sharing items such as cups, cutlery and lip balm. Avoid kissing, especially babies, until the sore has fully gone.
Yes, cold sores are caused by the herpes simplex virus, usually type 1 (HSV-1). It’s extremely common, and around two-thirds of people under 50 worldwide carry it. Most people catch it in childhood, and many never get symptoms. Having cold sores is nothing to be embarrassed about.
Why do I keep getting cold sores?
Once you have the cold sore virus, it stays in your nerve cells and can reactivate. Common triggers include being ill, stress, strong sunlight and periods. If you get cold sores often, a prescriber may suggest antiviral tablets, and keeping treatment at home means you can start it at the first tingle.
References
- World Health Organization. Herpes simplex virus. WHO; 2024. who.int
- NHS. Cold sores. NHS website; 2023. nhs.uk
- NHS. Aciclovir. NHS website; 2023. nhs.uk
- GlaxoSmithKline UK. Valtrex 500 mg film-coated tablets: Summary of Product Characteristics. Electronic Medicines Compendium; 2026. medicines.org.uk/emc
This article is intended for informational purposes only and does not replace professional medical advice. Always read the patient information leaflet supplied with your medication and speak to a healthcare professional if you have specific concerns.