A cold sore can be contagious from the first tingling or other early warning signs until it has completely healed. The exact length of an outbreak varies, but NHS guidance advises treating it as contagious until the cold sore has fully healed.
The risk is generally greatest when there are active blisters, particularly when they have burst and are releasing fluid. However, herpes simplex virus can sometimes be spread when there are no visible symptoms, so there is no way to remove the risk completely.
That is the short answer. The fuller picture is more useful because it explains what to do during each stage and which everyday concerns about cups, towels and surfaces are worth worrying about.
Key things to know
- Cold sores can be contagious from the first tingling or other early signs until the sore has completely healed
- The risk of spreading the virus is particularly important while there are active blisters or open sores
- A cold sore is not automatically no longer contagious just because the blister has crusted over
- Herpes simplex virus can sometimes be shed when there are no visible symptoms
- Avoid kissing and oral sex while you have a cold sore or the early tingling or itching that suggests one is developing.
Are Cold Sores Contagious?
Yes. Cold sores are caused by herpes simplex virus, usually HSV 1, and the virus can spread through close contact with an infected area or saliva.
Cold sores are particularly easy to spread when there is an active sore. This is why NHS advice is to avoid kissing while you have a cold sore and to avoid oral sex until the sore has completely healed.
It is also possible to carry HSV 1 without knowing it. Many people acquire the virus during childhood and never develop noticeable cold sores. Having the virus does not mean that someone will have regular outbreaks.
So, if you have a cold sore, the useful question is not whether everyone around you is at risk. It is about taking sensible precautions while the virus is most likely to be present at the skin surface.
Cold Sore Contagious Stages
How long are cold sores contagious at each point in an outbreak? There is no exact number of days that applies to everyone. The stages below are a general guide rather than a timetable.
| Stage | Roughly when | Contagiousness | What matters most |
|---|---|---|---|
| Tingle, or prodrome | Before the blister appears | Can be contagious | Avoid kissing and oral sex if the tingling feels like the start of one of your usual cold sores |
| Blister | Early part of the outbreak | Contagious | Avoid touching the blister and close contact with the affected area |
| Weeping, or open sore | After blisters burst | Particularly important to avoid contact | Fluid from an active blister or sore can contain the virus |
| Crusting | Later in the outbreak | Still potentially contagious | A crust does not necessarily mean the outbreak has completely healed |
| Healing | Until the skin is fully healed | Risk reduces as it heals, but continue precautions | Wait until the cold sore has completely healed before kissing or having oral sex |
When Are Cold Sores Most Contagious?
Cold sores can spread particularly easily when there are active blisters or open sores. When a blister breaks, the fluid can contain herpes simplex virus.
This is why it is especially important not to kiss anyone, have oral sex or touch the sore and then touch another person during this part of an outbreak.
There is no need to panic if you accidentally touch the sore. Wash your hands with soap and water afterwards and try not to touch the sore again.
When Do Cold Sores Stop Being Contagious?
NHS guidance advises treating a cold sore as contagious from the first tingling or other early signs until it has completely healed.
This means there is not a reliable point in the outbreak when you can simply look at the sore and say that it is safe before it has fully healed.
If there is still a crust, broken skin or an obvious sore, continue to avoid kissing and oral sex. Once the cold sore has completely healed, normal close contact can usually resume.
Is a Cold Sore Still Contagious After the Scab Falls Off?
The important point is whether the cold sore has completely healed, rather than whether the scab has simply fallen away.
If the skin is still broken, sore or visibly healing, it is sensible to continue taking precautions. NHS guidance uses complete healing as the point at which a cold sore is no longer considered contagious from that outbreak.
You do not need to wait for a particular number of extra days once the cold sore has genuinely healed. The appearance of the skin is more useful than a fixed timetable.
Contagious Before You Can See Anything
There are two different situations to understand here.
The first is the early warning stage. A cold sore can be contagious from the point when you first feel tingling or other signs that an outbreak is starting, even before a blister appears.
The second is asymptomatic shedding. Herpes simplex virus can sometimes be present on the skin or in saliva even when there is no visible cold sore. This means that transmission is possible without an obvious outbreak.
The exact amount of asymptomatic shedding varies between people and depends on how it is measured. For this reason, it is better not to rely on one percentage or one number to describe everyone's risk.
The practical message is simpler: you cannot always tell when HSV 1 is being shed. During a visible outbreak, however, you can take clear steps to reduce the chance of passing it on.
How Cold Sores Actually Spread
Close contact is the main concern. This includes:
- Kissing, which can spread HSV 1 through contact with the mouth or affected skin
- Oral sex, which can pass HSV 1 to the genitals and cause genital herpes
- Touching an active cold sore and then touching another person's mouth, eyes or broken skin
- Sharing items that have recently been in contact with saliva or the sore, such as lip products or cutlery, although direct contact is the more important route to focus on
NHS guidance specifically advises avoiding kissing and oral sex until the cold sore has completely healed.
Spreading It to Yourself
It is possible to transfer herpes simplex virus from an active cold sore to another part of your body by touching the sore and then touching another area.
This is one reason hand washing is important. NHS advice is to wash your hands with soap and water whenever you touch a cold sore.
One possible infection is herpetic whitlow, which affects a finger. It can happen after contact with a cold sore or another herpes blister.
The eye is more serious. Herpes simplex can affect the eye and may cause problems with vision. If you think a cold sore has spread to your eye, or you develop eye pain, redness or vision changes during an outbreak, seek same day medical advice.
If you wear contact lenses, take extra care not to touch your eyes after touching a cold sore.
Surfaces, Towels and Shared Items: Why Sources Disagree
This is one of those areas where online advice can become unnecessarily confusing.
HSV can survive outside the body for some time under certain conditions, but that does not mean that everyday objects such as door handles or toilet seats are a realistic way to catch a cold sore.
The more useful advice is to focus on direct contact with the sore, saliva and items that have just been in contact with the mouth.
During an outbreak, it is sensible not to share lip products, drinks or cutlery. Good hand washing is also important after touching the sore. NHS guidance focuses on these practical steps rather than asking people to disinfect every surface around them.
You do not need to avoid normal activities such as hugging someone simply because you have a cold sore. The main concern is direct contact with the sore or the mouth during an active outbreak.
Newborns and People at Higher Risk
Extra care is important around newborn babies because herpes simplex infection can be very serious in young babies. A person with a cold sore should not kiss a newborn baby. Everyone should wash their hands before handling a newborn, particularly after touching a cold sore.
If you have a cold sore, avoid direct contact between the sore and the baby. If you are breastfeeding and have a herpes blister on your breast, NHS guidance advises not feeding from the affected breast until the blister has healed.
If a newborn becomes unwell after possible exposure to herpes, seek urgent medical advice. Warning signs can include poor feeding, irritability, a high temperature, unusual sleepiness, or a rash or sores on the skin, eyes or inside the mouth.
People with weakened immune systems may also develop more serious or prolonged herpes infections. If you have a weakened immune system and develop a cold sore, speak to a healthcare professional for advice.
Reducing the Risk During an Outbreak
- Avoid kissing from the first tingling or other early signs until the cold sore has completely healed
- Avoid oral sex until the cold sore has completely healed
- Do not share lip products, drinks or cutlery during an active outbreak
- Wash your hands with soap and water after touching the sore
- Try not to pick, squeeze or touch the blister unnecessarily
- Avoid touching your eyes after touching the sore
- Take extra care around newborn babies and do not kiss them if you have a cold sore
- If you regularly get cold sores, speak to a pharmacist or prescriber if you need advice about treatment
These steps are about reducing the chance of spreading the virus. They cannot remove the risk completely because HSV can sometimes be shed when there are no visible symptoms.
Does Antiviral Treatment Shorten the Contagious Period?
Antiviral medicines such as aciclovir can be used for some cold sores. NHS guidance says aciclovir cream should be started as soon as possible after symptoms such as itching or tingling begin.
However, treatment should not be used as a reason to assume that you are no longer contagious. NHS guidance still advises avoiding kissing and oral sex until the cold sore has completely healed.
If your cold sores are very large, painful or keep coming back, a GP may consider antiviral tablets.
If you are getting frequent or severe outbreaks, or if the cold sore is affecting your eye, speak to a GP or prescriber rather than relying on repeated self treatment.
An online consultation with a UK registered prescriber may be one option for assessment where treatment is appropriate.
Medical Disclaimer
This page provides general information about cold sores and how they can spread. It is not personal medical advice and cannot confirm whether a particular sore is caused by herpes simplex virus.
Speak to a GP or pharmacist if you are worried about a cold sore, think it may be something else, or if it is very large or painful. NHS guidance also recommends medical advice if a cold sore has not started to heal within 10 days or if you have a weakened immune system.
Seek same day medical advice if you think a cold sore may be affecting your eye or vision.
If a newborn may have been exposed to herpes and becomes unwell, seek urgent medical help.
Suspected side effects from any medicine can be reported through the MHRA Yellow Card scheme.
