What are cold sores, and what causes them?

Cold sores are caused by a virus called herpes simplex type 1, one of the most common recurring viral infections in the world. Let's clear up some of the stigma and confusion that still exists.

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What are cold sores, and what causes them?

Cold sores are caused by a virus called herpes simplex type 1, one of the most common recurring viral infections in the world. Let’s clear up some of the stigma and confusion that still exists.

❓What are cold sores?

Cold sores (also called fever blisters) are small, fluid-filled blisters that usually appear on or around the lips. They usually break open, crust over, and heal within days to a couple of weeks.

Cold sores are most often caused by herpes simplex virus type 1 (HSV-1), a very common virus. (Occasionally, a different type of herpes causes cold sores, which we’ll cover below.) According to the World Health Organization (WHO), about 64% of people under age 50 worldwide carry HSV-1. Many people are exposed during childhood through common day-to-day contact, including exposure to saliva through things like goodbye kisses from relatives or shared cups or utensils.

After infection, the virus stays in nearby nerve cells near the base of the skull for life and can become active again later, causing recurring cold sores. Common triggers include illness, stress, fatigue, hormonal changes, and sun exposure. Many people notice tingling, burning, or itching before a sore appears.

Many people with HSV-1 never develop noticeable cold sores at all.

🔎Cold Sores vs. Canker Sores

These are often confused, but they are different conditions.

Cold sores:

• Are caused by a virus

• Usually appear on the lips or skin around the mouth

• Often begin as clusters of small blisters

• Are contagious

Canker sores:

• Are not caused by herpes viruses

• Occur inside the mouth (such as inside the cheeks, on the gums, or under the tongue)

• Usually appear as round white or yellow sores

• Are not contagious

If you are not sure which you have, the location is often the biggest clue. One confusing detail: when someone is first infected with HSV-1, they can sometimes develop sores inside the mouth during that initial infection.

🔎Oral Herpes vs. Genital Herpes

HSV-1 most often causes oral herpes (cold sores), while HSV-2 more commonly causes genital herpes, but the distinction is not perfect. Either virus can infect either location [archived link].

For example, an increasing number of genital herpes infections are caused by HSV-1, especially in younger adults. This type of infection occurs through oral-genital contact.

Even in the same person, HSV-1 can spread to other parts of the body like eyes, fingers, or even the brain. Fortunately, this is rare, but when it happens in the eyes or brain it can cause serious infections called herpetic keratitis and herpes simplex virus encephalitis.

🛡️Preventing Spread

Cold sores are most contagious when a sore is forming or present, especially when blisters are open or oozing. However, HSV-1 can sometimes spread even when no sore is visible. This is called asymptomatic shedding.

If you have an active cold sore, the following are recommended:

• Avoid kissing and oral-genital contact.

• Avoid sharing lip balm, utensils, cups, towels, or razors.

• Wash your hands after touching your face.

• Avoid touching your eyes or touching active cold sores.

• Be especially cautious around newborns (see below), people with weakened immune systems, and people with eczema (a common skin condition that causes dry, itchy skin), because HSV infections can sometimes become serious in these groups.

There are more recommendations about self-care on the American Academy of Dermatology Association’s page on cold sore treatment.

General precautions, whether or not you have an active cold sore:

• Be aware that transmission can happen without visible symptoms.

• Avoid sharing drinks or utensils with others, especially children (who may not have been exposed) or anyone concerned about being exposed to HSV1.

• Consider barrier methods like condoms and dental dams, which can reduce (but not fully get rid of) the risk of spreading HSV-1 or -2 during oral sex. Talking openly with partners about cold sores or herpes history can also help people make informed decisions together.

🔎Neonatal Herpes

Neonatal herpes (HSV infection in newborns) is a rare but serious condition. Babies are most commonly exposed to the virus during vaginal childbirth from a birthing parent with genital herpes. Either HSV-1 or HSV-2 can be transmitted to a baby this way. Newborns can also be exposed to HSV-1 after birth through contact with relatives or healthcare workers who have cold sores or are unknowingly shedding the virus.

The good news is that neonatal herpes is often preventable. It’s important for pregnant people to discuss their herpes history with their prenatal clinician and mention any oral or genital sores that develop during pregnancy. After birth, everyone can protect newborns by using good hand hygiene and being careful to avoid spread from anyone who has an active cold sore.

❓Why do some people get recurrent cold sores while others don’t?

This is one of the most interesting parts of HSV research.

Most people with HSV-1 don’t even know they have it. They don’t get cold sores, or don’t notice them. Other people get cold sores frequently. While we still don’t know all the answers, researchers think both genetics and environmental factors play a role in whether and how often the virus reemerges.

A 2014 study that is still widely cited today identified a specific difference (called a gene variant), which influences how often and how severely people with HSV-1 experience cold sore outbreaks, helping explain why some people get them often while others rarely do. Research since then has continued to uncover other genetic factors at play, and scientists are still actively working to understand the full picture.

Once someone already gets cold sores, things that can trigger another one include stress, illness, sun exposure, and changes in the immune system.

💊 Self-Care and Treatment

Can Medications Help? Yes, even though they do not get rid of the virus from the body.

If cold sores are frequent, severe, affecting your eyes, or affecting your quality of life, it is a good idea to talk with a clinician.

Antiviral medications such as acyclovir, valacyclovir, and famciclovir can shorten the length of time a cold sore is active and reduce symptom severity, especially when started very early, ideally at the first tingling or burning sensation.

Over-the-counter creams containing docosanol can help cold sores heal a little faster if used early and frequently, though prescription oral antiviral medications are more effective for many people.

There are also numbing agents or patches that might help you be more comfortable as your cold sore heals. You can ask your pharmacist for help if you’re unsure.

For some people, using sunscreen or SPF lip balm may help prevent cold sores triggered by sun exposure.

🧬Is there a cure or vaccine?

Not yet, but research is ongoing. This type of virus is tricky to treat because once someone is infected, the virus stays in the body for life.

Scientists are studying several approaches, including vaccines and gene-editing technologies aimed at targeting the virus while it is hiding out in nerve cells. As of now, there is no approved vaccine or cure for HSV-1.

🔬What about testing?

Routine testing is generally not recommended for HSV-1.

If you have mouth or skin sores that look like herpes, the fluid can be swabbed and tested to confirm if herpes is the cause and to know which type. This method usually uses a polymerase chain reaction (PCR) test. “PCR” may sound familiar from testing during the first couple of years of Covid - it’s the same type of test, but for HSV1 (or 2). For a common cold sore, though, your clinician probably won’t recommend PCR testing.

Blood antibody tests can be done even when no sore is present and look for signs that the immune system has responded to the virus. However, they are not always accurate and can sometimes miss an HSV infection or come back positive when someone does not actually have HSV. They also cannot reliably tell you when you were infected - a positive result may reflect an infection acquired years ago. Some tests also can’t distinguish between HSV-1 and HSV-2.

💚Final Thoughts

Cold sores are incredibly common. Getting them does not say anything about a person’s cleanliness or character. Most people are exposed to HSV-1 long before adulthood, and many never even know they carry it.

Good information and less stigma can make cold sores much easier to talk about and manage.

Love,

Those Nerdy Girls+&

ℹ️ Resources:

WHO - Herpes Simplex Virus

American Academy of Dermatology Association (AAD) - Cold sores: overview

AAD - Cold sores: signs and symptoms

AAD - Cold sore remedies dermatologists recommend

CDC - About Genital Herpes [archived link]

American Sexual Health Association (ASHA) - Five things you should know about Herpes

NHS - cold sores

Healthychildren.org - Cold sores in children

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