You're likely already aware of the main facts about cold sores - how to treat an outbreak, how long it lasts, and how to stop it spreading. But there's some lesser known facts about the condition that aren't common knowledge.
Here's six things about cold sores that you might not have heard before.
1. Most people catch the virus in childhood
Most people who go on to develop cold sores were infected with the herpes simplex virus type 1 (HSV-1) long before they can remember. It's commonly passed on from being kissed by a parent, grandparent or older sibling who has a cold sore.1
Studies of primary HSV-1 infection in children consistently find that most cases pass without a visible cold sore at all, with the virus only showing its effects much later when it first reactivates.2
This is why many people can carry HSV-1 for years without any obvious symptoms and have no idea when or how they picked it up. That first cold sore in adulthood can feel like it's appeared out of nowhere, but it's likely that the HSV-1 virus has been present, but dormant, since earlier in life.
2. "Cold sore" is a slightly misleading name
Despite the name, a cold sore has nothing to do with the common cold - the viruses that cause both are completely different biologically. The name most likely comes from the fact that having a cold, the flu, or any illness that puts the immune system under pressure is a common trigger that wakes up the dormant cold sore virus.1 Other well-known triggers include sunlight, tiredness, stress and hormonal changes such as menstruation, although in many cases there's no obvious trigger at all.1
It's an important distinction to know. Treating a cold with the usual paracetamol or decongestants won't do anything for the cold sore itself. A dedicated antiviral such as aciclovir cream is needed to bring an HSV-1 outbreak under control.
3. The HSV-1 virus hides in a nerve cluster near your jaw
Between outbreaks, HSV-1 doesn't disappear. It travels up sensory nerve fibres and settles into a bundle of nerve cells near the ear and jaw called the trigeminal ganglion, where it lies dormant until something reactivates it.3 This is also part of why cold sores tend to reappear in roughly the same spot each time. The virus is reactivating from the same local nerve supply rather than moving around the face at random.
The immune system keeps the dormant virus in check most of the time, but it's unable to clear it completely.3 That's why there's no cure for cold sores, only treatments such as aciclovir cream that shorten and ease an outbreak once the virus has already reactivated.
4. You can be contagious before you notice anything
Most advice says cold sores become contagious from the first tingle, and that's true for the majority of outbreaks. Less well known is that HSV-1 can also shed from the skin with no tingling, no blister and no visible sign at all. This is known as asymptomatic viral shedding, a recognised feature of how the virus reactivates.2
This doesn't happen often, and it isn't a reason to be overly anxious, but it does help explain why some people develop a cold sore despite being careful, or why the virus can occasionally pass between two people with no visible outbreak on either side. Keeping up good habits, such as not routinely sharing cups, cutlery or lip balm, offers more reliable protection than only being careful during an obvious outbreak.
5. The same virus behind cold sores can cause genital herpes
HSV-1 isn't confined to the mouth. It can also cause genital herpes if it's passed on during oral sex, and less commonly, HSV-2 (the virus behind most genital herpes) can cause a cold sore-like outbreak on the lips.4 In several countries, HSV-1 now accounts for a significant share of new genital herpes diagnoses, particularly in younger adults.5
This is one reason it's worth avoiding oral sex while a cold sore is active, alongside the better-known advice to avoid kissing during an outbreak.4 Unusual sores or blisters on the genitals are worth getting checked out, especially if there's history of cold sores in either partner. Genital herpes treatment is also available through Pharmica if it's needed.
6. Outbreaks usually ease off as you get older
The first year after catching HSV-1 tends to bring the most frequent outbreaks, since the body hasn't yet built up a strong antibody response to the virus.6 For most people, cold sores then become less frequent and less severe over time as the immune system gets better at keeping the virus under control.6
This doesn't mean outbreaks stop altogether, and some people continue to get several a year throughout adulthood, often linked to a trigger such as sun exposure or stress. If outbreaks are frequent, unusually severe, or becoming more common rather than easing over time, it's worth speaking to a pharmacist, who may suggest a more preventative approach, such as regular low-dose valaciclovir, rather than treating each outbreak individually.
Frequently Asked Questions
Is a cold sore the same thing as herpes?
Yes. A cold sore is a form of oral herpes, most often caused by the herpes simplex virus type 1 (HSV-1). It's part of the same virus family that causes genital herpes, and in some cases the two can even cross over, with HSV-1 causing genital herpes or HSV-2 causing a cold sore.
How did I suddenly get a cold sore when I've never had one before?
Most people are exposed to HSV-1 in early childhood, often without ever developing a visible cold sore, so the virus can already be present in your body for years before it first reactivates. A first visible cold sore in adulthood usually means the virus has reactivated for the first time, not that you've just caught it.
Can I still pass on a cold sore if I don't have any symptoms?
It's possible, though uncommon. HSV-1 can occasionally shed from the skin without any visible blister or tingling sensation, a process known as asymptomatic shedding. Good hygiene habits, such as not sharing cups or lip balm as a rule, offer protection beyond only avoiding contact during an obvious outbreak.
Will my cold sores ever go away for good?
There's currently no cure for HSV-1, so the virus stays dormant in the body for life once you've been infected. Most people find that outbreaks become less frequent and less severe over time, as the immune system gets better at keeping the virus under control.
Does a weakened immune system make cold sores worse?
Yes. Illness, stress, and anything that puts the immune system under pressure can trigger an outbreak, and people with a significantly weakened immune system, for example from certain medications or health conditions, can experience more frequent or more severe cold sores. If outbreaks become unusually persistent, widespread, or don't heal within the usual timeframe, it's worth speaking to a pharmacist or GP.
References
- NHS. Cold sores. nhs.uk
- National Center for Biotechnology Information (NCBI Bookshelf) / StatPearls. Herpes Simplex Type 1. ncbi.nlm.nih.gov
- National Center for Biotechnology Information (NCBI PMC). Immunological Control of Herpes Simplex Virus Type 1 Infection: A Non-Thermal Plasma-Based Approach. ncbi.nlm.nih.gov
- NHS inform. Cold sore. nhsinform.scot
- Journal of Clinical Virology. From HSV-2 to HSV-1: A change in the epidemiology of genital herpes. 2025. sciencedirect.com
- Cedars-Sinai. Herpes Simplex Virus (HSV) Mouth Infection. cedars-sinai.org
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.