You probably already know the basics about cold sores: how to treat an outbreak, how long it lasts and how to stop it spreading. But there are some lesser-known facts about them that most people haven't come across.
Here are six things about cold sores you might not have heard before.
1. Most people catch the virus in childhood
Most people who get cold sores were infected with the herpes simplex virus type 1 (HSV-1) long before they can remember. It's commonly passed on through a kiss from a parent, grandparent or older sibling who has a cold sore.1
Do not kiss babies while you have a cold sore. Newborns are especially vulnerable to the virus.
Studies of first HSV-1 infections in children consistently find that most pass without a visible cold sore at all. The virus only shows itself much later, when it first reactivates.2
That's why many people carry HSV-1 for years without any obvious symptoms, with no idea when or how they picked it up. Your first cold sore as an adult can feel like it's come out of nowhere, but the virus has most likely been there, dormant, since earlier in life.
2. "Cold sore" is a slightly misleading name
Despite the name, cold sores have nothing to do with the common cold. The viruses behind them are completely different.
The name most likely comes from the fact that a cold, flu or any illness that puts your immune system under pressure is a common trigger for waking up the dormant virus.1 Other well-known triggers include sunlight, tiredness, stress and hormonal changes such as periods, though often there's no obvious trigger at all.1
Sunlight a trigger for you? A lip balm with SPF can help keep outbreaks at bay.
It's a useful distinction to know. Your usual cold remedies, like paracetamol or decongestants, won't do anything for the cold sore itself. An antiviral such as aciclovir can help it heal faster.
3. The HSV-1 virus hides in a nerve cluster in your head
Between outbreaks, HSV-1 doesn't disappear. It travels up your sensory nerve fibres and settles in a bundle of nerve cells called the trigeminal ganglion, which sits deep inside your head in front of your ear. There, it lies dormant until something reactivates it.3
That's part of why cold sores tend to come back in roughly the same spot each time. The virus is reactivating from the same local nerve supply, rather than moving around your face at random.
Your immune system keeps the dormant virus in check most of the time, but it can't clear it completely.3 That's why there's no cure for cold sores. Treatments such as aciclovir cream shorten and ease an outbreak once the virus has reactivated.
Same spot every time? That's the nerve the virus lives in, not bad luck.
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 most outbreaks. Less well known is that HSV-1 can also shed from your skin with no tingling, no blister and no visible sign at all. This is called asymptomatic viral shedding, and it's a recognised part of how the virus reactivates.2
Felt the tingle? Start treatment straight away. That's when antiviral creams work best.
It isn't a reason to be overly anxious. But it does help explain why some people get a cold sore despite being careful, or why the virus can occasionally pass between two people with no visible outbreak on either side.
Good everyday habits, like not routinely sharing cups, cutlery or lip balm, give you 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 your mouth. It can also cause genital herpes if it's passed on during oral sex. 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, especially in younger adults.5
That's one reason to avoid oral sex while you have a cold sore, alongside the better-known advice not to kiss anyone during an outbreak.4 Unusual sores or blisters on your genitals are worth getting checked, especially if either partner has a history of cold sores. Genital herpes treatment is also available through Pharmica if you need it.
6. Outbreaks usually ease off as you get older
The first year after catching HSV-1 tends to bring the most frequent outbreaks, because your 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
That doesn't mean outbreaks stop altogether. Some people keep getting several a year throughout adulthood, often linked to a trigger like sun exposure or stress.
Outbreaks frequent, unusually severe, or getting more common rather than easing? Speak to a pharmacist. They may suggest a preventive approach, such as regular low-dose valaciclovir, rather than treating each outbreak separately.
Cold sore near your eye, or one that hasn't healed after 10 days? Get it checked by a GP.
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.