You get cold sores from the herpes simplex virus type 1 (HSV-1), which spreads through close personal contact — most commonly kissing someone who has an active cold sore, or sharing utensils, towels, razors or lip balm with them. Once infected, the virus stays dormant in your facial nerves for life and can reactivate as new cold sores, typically triggered by sunlight, stress, illness or hormonal changes. Cold sores are most contagious from the first tingle until the blister has fully scabbed over.
How Cold Sores Spread: The Basics
Cold sores are small, painful blisters that appear on or around the lips, caused overwhelmingly by herpes simplex virus type 1. The virus spreads through direct skin-to-skin contact with an infected area or through contact with infected saliva. The NHS guidance on cold sores notes that most adults in the UK carry HSV-1 — many were infected in childhood and never develop noticeable cold sores at all.
Crucially, you cannot get a cold sore “from nowhere” in the way you catch a cold from the air. Infection requires contact with the virus. But because HSV-1 is so widespread and often silent, most people cannot pinpoint exactly when or from whom they caught it.
The Common Ways People Get Cold Sores
Kissing
Kissing someone with an active cold sore — even a tingle-stage one with no visible blister yet — is the commonest route of transmission. The virus passes easily through the moist skin of the lips. Avoid kissing anyone while you have a cold sore, and politely decline kisses from others who have one, particularly on or near the mouth.
Sharing Personal Items
HSV-1 can survive briefly on objects, so sharing lip balm, lipstick, razors, towels, cutlery, cups or toothbrushes with someone who has an active cold sore carries a real — if smaller — risk. In practice, saliva on a shared water bottle or a borrowed lip balm is a plausible transmission route, especially among teenagers and young adults who share freely.
Oral Sex
HSV-1 can spread from the mouth to a partner’s genitals through oral sex, causing genital herpes — and HSV-2 can likewise cause cold sores around the mouth, though this is less common. Using barrier protection during oral sex when either partner has an active outbreak reduces this risk. This is one of the least-discussed but most important transmission routes to understand.
Childhood Contact
Many people acquire HSV-1 in early childhood through affectionate contact — kisses on the face from relatives who carry the virus. Because childhood infections are often symptomless, the virus can lie dormant for decades before a first cold sore appears in adulthood, which is why a “first” cold sore in your 30s does not mean a recent infection.
Why Cold Sores Keep Coming Back
After the first infection, HSV-1 retreats into the trigeminal nerve ganglion near your cheek, where it sleeps indefinitely. Your immune system keeps it suppressed most of the time, but certain triggers can wake it up, sending the virus back down the nerve to the lip surface. Common triggers include:
- Sunlight and sunburn: UV exposure on the lips is one of the strongest triggers — lip balm with SPF 30 helps prevent recurrences.
- Stress and fatigue: both dampen immune control of the virus.
- Illness: colds, flu and fever classically precede outbreaks (hence “cold” sore).
- Hormonal changes: some women notice outbreaks around menstruation.
- Lip injury: dental work, chapped lips or aggressive exfoliation can trigger one.
- Weakened immunity: people on immunosuppressant medication get more frequent, severe outbreaks.
How to Avoid Spreading (or Catching) Cold Sores
- Do not kiss anyone — especially babies, whose immune systems are immature — while you have a cold sore.
- Do not share lip products, towels, razors, cutlery or drinks during an outbreak.
- Wash your hands after touching your cold sore, and avoid touching your eyes — HSV-1 can cause a serious eye infection.
- Do not pick or squeeze the blister; this prolongs healing and increases spread.
- Use a separate towel and pillowcase during outbreaks, and wash them hot.
- If you are prone to sun-triggered outbreaks, wear SPF lip balm daily.
Treating a Cold Sore Quickly
Cold sores usually clear on their own in 7–10 days, but early treatment shortens this. At the first tingle — before the blister appears — apply aciclovir 5% cream (available over the counter, around £4–£7) five times daily for 4–5 days. It works best the earlier you start. Hydrocolloid cold sore patches protect the blister, reduce the urge to touch it, and can subtly conceal it. Keep the area moisturised with plain lip balm to prevent cracking, and take paracetamol or ibuprofen if it is painful. For frequent or severe outbreaks, your GP can prescribe oral antivirals or suppressive daily therapy.
When to See a GP or Pharmacist
See a GP if cold sores spread to your eyes, if outbreaks are very frequent or severe, if the sore does not start healing within 10 days, or if you have a weakened immune system. Babies under six months with any blistering around the mouth need prompt medical attention. Your pharmacist can advise on creams and patches for straightforward cases — you do not need a GP appointment for a typical cold sore.
Cold Sores vs Other Lip Problems
Not every lip blister is a cold sore, and the distinction affects treatment. Cold sores follow a recognisable script: tingling or burning for a day, then a cluster of small fluid-filled blisters on the lip border that crust over within days. Impetigo causes honey-coloured crusts but is bacterial and needs antibiotics. Angular cheilitis produces painful cracks at the corners of the mouth — often fungal or related to vitamin deficiency rather than HSV. Contact dermatitis from a new lip balm or toothpaste causes itchy, scaly irritation without the blister-then-scab sequence. Chapped lips in winter are simply dryness. If your “cold sore” does not tingle first, does not blister, or does not heal within two weeks, get it checked — persistent non-healing lip lesions occasionally need biopsy to rule out skin cancer, particularly in older adults with heavy sun exposure.
Frequently Asked Questions
Are cold sores an STI?
Cold sores themselves are not classified as a sexually transmitted infection, but the virus that causes them (HSV-1) can be transmitted sexually through oral sex and cause genital herpes. The label matters less than understanding the transmission routes.
Can you get cold sores from sharing drinks?
It is possible but uncommon — the virus does not survive long on surfaces, and transmission needs a reasonable viral load. Sharing lip balm or kissing carries far more risk than sharing a glass, but avoiding sharing during an active outbreak is still sensible.
Are cold sores contagious before the blister appears?
Yes. You are contagious from the first tingling or itching sensation (the prodrome stage) until the blister has completely scabbed over and healed. Asymptomatic shedding — contagiousness without any symptoms — can also occur, though the risk is much lower than during an outbreak.
Can cold sores spread to other parts of the body?
Yes, if you touch an active cold sore and then touch broken skin elsewhere — the eyes are the most concerning site. Always wash your hands after touching the area, and avoid contact sports like wrestling or rugby during an outbreak, as the virus can spread to facial skin (herpes gladiatorum).
Do cold sores mean I have herpes forever?
In the strict virological sense, yes — HSV-1 remains in your nerves for life. But for most people this means nothing more than an occasional lip blister every year or two, and many carriers never get a visible cold sore at all. It does not affect your general health.
Conclusion
You get cold sores from HSV-1, caught through kissing, shared personal items, oral sex or childhood contact — and once you have the virus, it can reactivate periodically for life. The good news is that transmission is easy to prevent with basic hygiene, outbreaks are treatable with pharmacy antivirals, and recurrences can be reduced by managing triggers like sun exposure and stress. Understanding how cold sores spread puts you firmly in control of them.
