Updated on April 24, 2024
7 min read

Cold Sores

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What are Cold Sores?

Cold sores, sometimes called fever blisters, are caused by the herpes simplex virus (HSV). They’re one of the most common oral conditions, with most cold sores developing on and around the lips.

There are two types of HSV:

  • HSV-1 ⁠— Usually the cause of cold sores (oral herpes)
  • HSV-2 ⁠— More commonly associated with genital warts (genital herpes)

It’s estimated that one-third of the world population has had at least one cold sore.1 Many people also have a herpes infection but no symptoms.

What Do Cold Sores Look Like?

Cold sores are small blisters filled with fluid. They typically appear on and/or around your lips. You may have multiple sores at once.

Cold sores may appear swollen when they first form, but as the blisters erupt, they become shallow and begin to ooze. Then they begin to form scabs.

The entire process, from the earliest symptoms to complete healing, may take one to weeks. It’s usually divided into five stages:

  1. Initial symptoms — For a day or two leading up to a cold sore forming, you may feel an itching or tingling sensation on your lips. The area may begin to appear red.
  2. Formation — After that initial day or two, you’ll begin to see the blister form, typically on or near your lips. There may be more than one.
  3. Rupture — Another day or two after appearing, the blister will burst, becoming an open sore. This can be painful.
  4. Scabbing — After the blister breaks open, it begins to crust over. A scab will form over the next few days.
  5. Healing — At least a week after the initial symptoms, the scab will fall off, and your skin will heal completely.

What Causes Cold Sores?

Cold sores result from infection with herpes simplex virus type 1 (HSV-1). The infection is incurable, but it’s often asymptomatic. People of all ages and backgrounds can be affected by HSV-1.

People with HSV-1 may experience one or more cold sore outbreaks throughout their lives, but some never show symptoms. Outbreaks are often triggered by additional factors, such as:

  • A cold or other illness
  • Hormonal changes
  • Dietary changes
  • Stress
  • Fatigue
  • Overexposure to cold wind or sunlight
  • Skin or lip injury

A weakened immune system can also be a factor. Chemotherapy, organ transplant (anti-rejection) medication, and HIV/AIDS can all make outbreaks more likely.

Other Symptoms of Cold Sores

Aside from the blisters themselves, cold sores can come with additional symptoms. These are especially common when a person is first infected and generally decrease with future outbreaks. They include:

  • Fever
  • Headache
  • Malaise (generally feeling ill)
  • Muscle aches
  • Sore throat
  • Swollen lymph nodes
  • Painful gums, which may have visible sores themselves (herpetic gingivostomatitis)

How Do Cold Sores Spread?

Herpes simplex virus is contagious and can easily spread from person to person. It mainly spreads through saliva or contact with an infected person’s mouth. This means that all of the following can spread cold sores:

  • Kissing
  • Oral sex
  • Sharing food, drinks, eating utensils, or vapes

It’s best to avoid the above activities if you have an active cold sore. Otherwise, you’ll risk spreading the virus to the other person.

Even though HSV-1 isn’t usually associated with genital warts (unlike HSV-2), it can cause them if spread via oral sex.

Canker Sores vs. Cold Sores: What’s the Difference?

Canker sores (or aphthous ulcers) are common oral lesions and are sometimes confused with cold sores. Here are some of the main differences:

  • Canker sores are on the inside of the mouth ⁠— Unlike cold sores, they don’t appear on the outside of the lips. They generally occur on the inner lip or the base of the gums.
  • Cold sores and canker sores look different ⁠— Canker sores are round or oval and have a white or yellowish center with a red border. Cold sores are small blisters that often appear in clusters.
  • Canker sores aren’t contagious ⁠— To prevent them, you should maintain a healthy diet, keep up with oral hygiene, and minimize stress.
  • Unlike cold sores, canker sores don’t burst, ooze, crust over, or scab However, they do gradually heal, becoming smaller and less painful.

Stress and other lifestyle factors can trigger cold sores and canker sores, but a virus ultimately causes cold sores. Canker sores aren’t a sign of a viral infection. However, H. pylori bacteria may be involved, as with stomach ulcers.

When to See a Doctor

Cold sores aren’t always a major cause for concern, especially if you’ve had manageable outbreaks in the past.

However, you should visit your doctor if:

  • You get cold sores frequently or have intense outbreaks
  • Your cold sores don’t heal within two weeks
  • You have symptoms such as a persistent headache, chronic fatigue, fever, or chills

Your doctor can easily diagnose cold sores and recommend appropriate treatment.

Unfortunately, there is no permanent cure for cold sores. Herpes simplex is a lifelong infection. However, your doctor can prescribe medications and recommend home remedies to reduce discomfort and encourage healing.

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Cold Sore Treatment

While there’s no cure for the herpes simplex virus, you can treat cold sores and make outbreaks more manageable. Your doctor may prescribe an antiviral pill or topical cream to help reduce healing time.

Cold sore patches or a topical ointment like Abreva (docosanol) can also help cold sores heal faster. Your doctor may recommend pain medication or fever reducers as well.

Keep your lips moist as a cold sore heals to prevent cracking and bleeding. This will help promote healing.

How to Prevent Cold Sores 

If someone you know has a cold sore, it’s best to avoid the following until their symptoms have fully resolved:

  • Kissing
  • Oral sex
  • Sharing food, drinks, or eating utensils
  • Sharing makeup, towels, or any other objects that make contact with their mouth

If you have had cold sores in the past, you can’t guarantee that you won’t have another outbreak in the future.

However, keeping your immune system strong and avoiding known triggers may help. You can be proactive by eating a balanced diet, managing stress, and getting good sleep.

Can Cold Sores Have Complications?

Cold sores themselves are unlikely to have severe complications. However, the virus that causes them can.

In rare cases, herpes simplex infection can affect the brain, eyes, or other organs. This can lead to various complications, including:

  • Life-threatening brain inflammation
  • Blindness
  • Organ failure

These complications are more common in people with weakened immune systems, such as those with HIV/AIDS. You should let your doctor know if you have persistent symptoms that affect areas other than your mouth (such as chronic fatigue, a headache, or fever).

What’s the Outlook for Cold Sores?

Oral herpes is incurable but easily managed. Taking action early can relieve the symptoms and encourage healing if you have an occasional cold sore outbreak. In any case, cold sores in themselves aren’t life-threatening.

In addition, many people (possibly the majority of the world’s population) have HSV-1, and not all develop cold sores.

However, in rare cases, HSV-1 infection can spread to other parts of the body, leading to severe complications. Tell your doctor if you have a persistent headache, fever, or other symptoms.


Cold sores, or fever blisters, are caused by the herpes simplex virus (type 1 in most cases, but sometimes type 2). Most people worldwide have been infected with the herpes virus, but many never show symptoms.

Once you’re infected, cold sores can be brought on by stress, a weakened immune system, and other factors. Medication and home remedies can help speed up the healing process, but there’s no cure, so the sores may return.

Talk to your doctor if you have intense cold sore outbreaks or symptoms that affect your daily life, such as a fever or headache.

Last updated on April 24, 2024
6 Sources Cited
Last updated on April 24, 2024
All NewMouth content is medically reviewed and fact-checked by a licensed dentist or orthodontist to ensure the information is factual, current, and relevant.

We have strict sourcing guidelines and only cite from current scientific research, such as scholarly articles, dentistry textbooks, government agencies, and medical journals. This also includes information provided by the American Dental Association (ADA), the American Association of Orthodontics (AAO), and the American Academy of Pediatrics (AAP).
  1. Saleh et al. “Herpes Simplex Type 1.” StatPearls, 2023.
  2. Crimi et al. “Herpes Virus, Oral Clinical Signs and QoL: Systematic Review of Recent Data.” Viruses, 2019.
  3. Woo, Sook-Bin, and Challacombe, S.J. “Management of recurrent oral herpes simplex infections.” Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology, 2007.
  4. Kim et al. “A case report of severe systemic herpes simplex virus-1 (HSV-1) infection with multi-organ involvement after a course of oral corticosteroid treatment.” BMC Infectious Diseases, 2022.
  5. Marcocci et al. “Herpes Simplex Virus-1 in the Brain: The Dark Side of a Sneaky Infection.” Trends in Microbiology, 2020.
  6. Rotstein, I., and Katz, J. “Acute periapical abscesses in patients with herpes simplex type 1 and herpes zoster.” Journal of Oral Medicine and Oral Surgery, 2022.
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