Cold sores — treatment and triggers
Reviewed by the My London Pharmacy clinical team, Michelle Chuku, Pharmacist Independent Prescriber
·29 July 2026
·7 min read
Quick answer
Cold sores are small blisters around the lips caused by the herpes simplex virus, which stays in the body and can reactivate. They usually clear within seven to ten days. Antiviral creams and tablets work best when started at the first tingling sign, and a clinician can advise if outbreaks are frequent or severe.
What causes cold sores
Cold sores are caused by the herpes simplex virus, most often type 1. It is very common, and many people carry the virus without ever realising, having picked it up in childhood. After the first contact, the virus stays dormant in the nerves and can reactivate from time to time, producing an outbreak around the lips or mouth.
The virus spreads through close contact, such as kissing or sharing items like cutlery, lip balm or towels. It is most easily passed on when a blister is present, but the aim of managing cold sores is comfort and reducing spread rather than removing the virus, which remains in the body for life. Understanding this helps set realistic expectations: treatment shortens and eases outbreaks rather than curing the underlying infection.
Carrying the virus is extremely common and says nothing about a person's hygiene or general health. Many people never have a single visible cold sore, while others have them from time to time throughout life. The first ever episode is sometimes the most uncomfortable, occasionally with a sore mouth and feeling generally unwell, whereas later reactivations tend to be smaller and more predictable, often appearing in the same spot each time.
How a cold sore develops
Cold sores tend to follow a predictable pattern over a week to ten days:
- A tingling, itching or burning feeling before anything is visible
- Small fluid-filled blisters appearing, usually at the edge of the lips
- The blisters bursting and forming a raw, weeping area
- A scab developing, which gradually dries and heals without scarring
The early tingling stage is important, because starting treatment at this point tends to give the best results. Once blisters have fully formed, treatment can still ease symptoms but is less likely to shorten the outbreak dramatically. Learning to recognise your own early warning signs is one of the most useful things you can do.
Common triggers to be aware of
Outbreaks are often set off by a recognisable trigger. Common ones include:
- Being run down, tired or unwell, such as during a cold or other infection
- Stress or emotional strain
- Strong sunlight or ultraviolet exposure
- Cold or windy weather
- Hormonal changes, for example around a period
Noticing your own patterns can help you anticipate and reduce outbreaks. Using a lip balm with sun protection, keeping well rested, and taking extra care when you are tired or stressed may reduce how often cold sores appear. Some people find that once they identify a main trigger, simple preventive habits make a noticeable difference over time.
Keeping a brief note of when outbreaks happen, and what was going on beforehand, can reveal patterns that are easy to miss day to day. For some people the link is clear, such as bright sun on a skiing or beach holiday; for others it is a combination of being tired, stressed and run down at the same time. Where sunlight is a trigger, applying a lip balm with a sun protection factor before going outside is a practical step that many people find helpful.
How cold sores are treated
Many cold sores heal on their own, but antiviral treatment can ease symptoms and may shorten an outbreak, especially when started early. Antiviral creams containing Aciclovir are applied to the affected area several times a day and work best at the first tingle, before the blister appears.
For outbreaks that are more troublesome, a clinician may consider antiviral tablets such as Aciclovir in oral form or Valaciclovir, which act on the virus from within the body and can be helpful for larger or more painful outbreaks. Cold sore patches can protect the area, reduce the risk of spreading the virus and help the skin heal. Simple pain relief, keeping the area clean and avoiding picking at the scab all support comfort and recovery.
It is worth being realistic about what treatment can achieve. Antiviral creams and tablets can ease symptoms and may shorten an outbreak, especially when started at the very first tingle, but they do not remove the virus from the body, so further outbreaks can still happen. Creams are available from pharmacies for straightforward cold sores, while tablets are prescribed after assessment for outbreaks that are more troublesome. A pharmacist can help you choose a suitable option and check it is right for you before you start.
When outbreaks are frequent or severe
Most people have occasional cold sores that settle without much trouble. If you have frequent outbreaks, ones that are unusually painful or widespread, or that are slow to heal, it is worth speaking to a clinician for a proper review.
In some cases a longer or preventive course of antiviral treatment may be discussed, particularly for people whose outbreaks are triggered predictably, such as by strong sunlight. This is decided individually, taking into account how often outbreaks occur, how much they affect you and your general health.
If cold sores are having a real impact on your confidence or daily life, that in itself is a good reason to seek advice, even if each individual outbreak is not severe. A clinician can review how often they occur and what tends to set them off, and discuss whether a preventive approach around known triggers, such as periods of strong sun exposure, might reduce how frequently they appear.
Easing discomfort during an outbreak
Alongside any antiviral treatment, a few simple measures can make an outbreak more comfortable while it heals. Keeping the area clean and leaving the scab to come away on its own reduces the risk of irritation and helps the skin recover without scarring. If the cold sore is sore, ordinary pain relief such as paracetamol, used as directed and if suitable for you, can help, and a cold sore patch can protect the area and make eating and talking a little easier.
Lips can become dry and cracked during an outbreak, so a plain lip balm can keep them comfortable, and it is sensible to avoid acidic or salty foods if they sting. There is no need to change your diet dramatically or follow the restrictive routines sometimes suggested online, as the evidence for these is weak. Gentle, sensible care while the outbreak runs its course, together with early antiviral treatment when you feel the first tingle, is the most dependable approach for most people.
Reducing the risk of spreading
Because cold sores are contagious, a few simple steps help protect others while one is present. Avoid kissing and close skin contact, and do not share items that touch the mouth, such as cutlery, cups, towels or lip products.
Wash your hands after touching a cold sore, and take particular care around newborn babies and anyone with a weakened immune system, as the virus can cause more serious problems in these groups. Avoiding touching your own eyes after touching a cold sore is also sensible, as the virus can affect the eye.
During an outbreak it also helps to avoid touching or picking at the blister more than necessary, both to reduce the risk of spreading the virus to other areas and to let the skin heal cleanly. Washing your hands before applying any cream, and again afterwards, is a simple habit that protects both you and the people around you.
When to seek medical advice
Seek advice if a cold sore has not healed within ten days, keeps returning, or is very large or painful. It is especially important to get help if a cold sore spreads to the eye, as this can affect vision and needs prompt treatment.
People with a weakened immune system, and newborn babies, are more vulnerable to complications from the herpes virus, so any suspected cold sore in these situations should be assessed without delay. A pharmacist can offer advice on treatment for straightforward cold sores and help you decide whether you need to see a clinician.
Frequently asked questions
Can cold sores be cured?
The herpes simplex virus stays in the body for life, so cold sores cannot be removed entirely. Treatment focuses on easing symptoms, speeding healing and reducing how often outbreaks occur.
When should I start cold sore treatment?
Antiviral creams and tablets work best when started at the first tingling or itching sensation, before blisters appear. Beginning early gives the best chance of a shorter, milder outbreak.
Are cold sores contagious?
Yes. The virus spreads through close contact and is most easily passed on when a blister is present. Avoid kissing and sharing items like cutlery or lip balm during an outbreak.
Should I see someone about frequent cold sores?
If outbreaks are frequent, severe or slow to heal, a clinician can review your history and discuss whether a longer or preventive course of antiviral treatment may help.
When is a cold sore serious?
Get prompt help if a cold sore spreads to the eye, does not heal within ten days, or occurs in someone with a weakened immune system or a newborn baby.