Cold sores: why you get them and what actually helps

If you get cold sores, you already know the feeling that comes first. A tingle, an itch, a tightness on the lip that tells you what the next week looks like before anything is visible.

Here is what is actually happening, why it keeps happening, and which of the many things sold for cold sores are worth your money.

What a cold sore is

Cold sores are caused by herpes simplex virus type 1, usually shortened to HSV-1.

That word does a lot of unnecessary damage. HSV-1 is extraordinarily common. The World Health Organization estimates that about two thirds of people under 50 worldwide carry it, roughly 3.7 billion people.[1] Most picked it up in childhood from an ordinary kiss from a relative, and most people who have it never develop a single visible sore.

It is not a reflection of anything about you, and it is not the same as genital herpes, which is more often HSV-2. The two are related viruses that behave differently and live in different places.

Why it comes back

This is the part people find frustrating, and it is worth understanding.

After the first infection, HSV-1 does not leave. It travels along a nerve and settles in a cluster of nerve cells near the base of your skull, where it sits dormant and invisible to your immune system. Something eventually reactivates it. The virus travels back down the same nerve to roughly the same patch of skin, which is why your cold sores appear in the same spot nearly every time. No treatment currently available clears the dormant virus. What treatment does is shorten and soften each outbreak, and in some cases prevent most of them.

The five stages

Knowing these matters, because the window where treatment works best is the first one.

Tingle. Hours to a day before anything appears. Itching, burning or tightness. This is the virus already travelling down the nerve.

Blister. Small fluid-filled blisters appear, usually clustered.

Weeping. The blisters break open. This is the most contagious stage and the most uncomfortable.

Crusting. A scab forms. It often cracks and bleeds, which is why this stage drags.

Healing. The scab falls away. Skin underneath may stay pink for a week or two.

Left alone, the whole cycle runs about seven to fourteen days.[2]

What triggers an outbreak

Most people eventually work out their own pattern. The usual ones:

1. Sunlight. One of the most common triggers, and the most preventable.[2]
2. Stress, the sustained kind more than a single bad day.
3. Illness, which is where the name comes from.
4. Fatigue and poor sleep.
5. Hormonal shifts, including around menstruation.
6. Lip injury, including dental work and chapping.

Keeping a rough note of what preceded your last few outbreaks is more useful than it sounds. Triggers are individual, and once you know yours, some become avoidable.

What actually works

Prescription antivirals, started early. This is the single most effective option. Acyclovir, valacyclovir and famciclovir all interfere with the virus replicating.[2] Started at the tingle stage, they can meaningfully shorten an outbreak and sometimes stop it developing at all.

The crucial word is early. The American Academy of Dermatology advises starting treatment when you first feel tingling or burning, or as soon as the sore appears.[2] Started once blisters have fully formed, the benefit drops considerably. This is why people who get cold sores regularly often keep a prescription on hand rather than requesting one each time.

Docosanol, sold as Abreva. Available without a prescription. In the multicentre trial behind its approval, docosanol 10% cream shortened mean healing time to 5.7 days against 7.3 days for placebo, a difference of about a day and a half.[3] Some independent reviewers have judged the effect more modest than that. Either way, it needs to be applied at the first sign to do anything at all.

Cold compresses for discomfort, and ibuprofen or acetaminophen for pain.

Lip balm with SPF 30 or higher, daily and ongoing. The AAD notes that year-round use may help prevent outbreaks in people whose cold sores are sun-triggered, and can help an existing one heal.[2]

What does not work

Most of what is sold for cold sores has little evidence behind it.

Lysine supplements are widely recommended, but the studies behind them are small and inconsistent, and dermatology guidance points to antiviral medication rather than supplements.[2] Not harmful, but not the answer.

Toothpaste, rubbing alcohol and tea tree oil applied directly tend to irritate already inflamed skin and extend the healing time.

Picking the scab restarts the healing clock and increases the chance of scarring and secondary infection.

When outbreaks are frequent

If you are getting six or more outbreaks a year, treating each one as it arrives is not the only option.

Daily suppressive antiviral therapy, taken continuously at a low dose rather than as needed, reduces how often outbreaks occur. The AAD identifies six or more outbreaks a year as the point where daily low-dose antiviral treatment is worth considering.[2] For people whose cold sores are frequent enough to interfere with work or social life, it changes the picture entirely.

It is worth a conversation if your outbreaks are regular.

Staying contagious, and staying careful

Cold sores spread through direct contact with the sore or the fluid in it. You are most contagious from the first blister through to full crusting.

While you have an active sore, avoid kissing, do not share drinks, cutlery, towels or lip products, and wash your hands after touching your face. The AAD also advises applying any medication with a clean cotton swab rather than your finger, and throwing away lip products used during an outbreak once it clears.[2]

Two situations deserve more caution than they usually get.

Never let an active cold sore near a newborn. HSV in a newborn can be severe. A cold sore is a good reason to skip holding or kissing a new baby until it has fully healed.

Keep it away from your eyes. Touching the sore and then your eye can transfer the virus, and herpes affecting the eye can damage vision. Any eye pain, redness or light sensitivity during an outbreak needs same-day attention from an eye doctor.

When to see someone

Most cold sores need nothing more than time and an antiviral. Get seen if:

1. A sore is near or in your eye, or you have eye symptoms
2. Sores spread widely across your face
3. You have a weakened immune system
4. An outbreak lasts beyond two weeks[2]
5. The sore looks infected, with increasing pain, warmth or yellow crusting
6. You are getting them frequently and want to stop the pattern

The short version

Cold sores are caused by a very common virus that stays with you and reactivates when conditions allow. You cannot clear it, but you can shorten outbreaks substantially if you treat at the first tingle, and you can reduce how often they happen if they are frequent.

The timing is the thing most people get wrong. By the time the blister is visible, the best window has passed.

If you get cold sores and want treatment on hand so you can start at the first sign, a clinician can review your history and send a prescription to your pharmacy. See cold sore treatment online.

References

World Health Organization. Globally, an estimated two-thirds of the population under 50 are infected with herpes simplex virus type 1. 28 October 2015. https://www.who.int/news/item/28-10-2015-globally-an-estimated-two-thirds-of-the-population-under-50-are-infected-with-herpes-simplex-virus-type-1

American Academy of Dermatology Association. Cold sores: Diagnosis and treatment. https://www.aad.org/public/diseases/a-z/cold-sores-treatment

Sacks SL, Thisted RA, Jones TM, et al. Clinical efficacy of topical docosanol 10% cream for herpes simplex labialis: a multicenter, randomized, placebo-controlled trial. Journal of the American Academy of Dermatology, 2001. https://www.jaad.org/article/S0190-9622(01)30676-X/abstract

Medically reviewed by Haroon Arshad, MD, MBA, Medical Director, Qare Medical Group, P.C. · Board-Certified in Family Medicine

Last reviewed: October 2026