What Are Cold Sores? Symptoms, Causes, Diagnosis, Treatment, and Prevention

Cold sores are small, painful blisters that typically form on or near the lips. These tiny fluid-filled blisters are sometimes called fever blisters or oral herpes. (1)

Cold sores are highly contagious and can spread through saliva or skin contact. It’s a common condition, with some people experiencing their first outbreak during childhood. (2)

There’s no cure for cold sores, but the good news is that many cold sores usually go away on their own in a week or two and don’t leave a trace. (1)

To relieve pain and accelerate healing, medications, and home remedies can help. (3)

Signs and Symptoms of Cold Sores

Symptoms of cold sores vary, with the first exposure or primary outbreak usually being the most severe, says Allison Arthur, MD, a board-certified dermatologist based in Orlando, Florida.

First-time cold sore symptoms may include: (4)

  • Painful blisters on the lips, cheeks, mouth, nose, or throat (which eventually pop and form scabs)
  • Gingivostomatitis (inflammation of the gums and mouth)
  • Mouth and throat pain
  • Swelling in the neck
  • Fever and body aches

You’ll still have painful blisters with recurrent outbreaks, but the more severe symptoms, like body aches and a fever, are less likely to return.

It’s important to note that while cold sores typically form outside of the mouth, these sores can form inside the mouth during your first outbreak. This is known as acute herpetic gingivostomatitis. (4) For this reason, you might initially mistake a first-time cold sore for a canker sore. Canker sores are ulcers that form on the mucous membranes inside the mouth or on the tongue. (5)

A cold sore can develop anytime after you’re first infected with a herpes simplex virus (HSV). You may also notice early signs of an outbreak one or two days before a blister appears.

Early symptoms of a cold sore may include: (4)

  • Pain
  • Burning
  • Tingling
  • Itching

The blister appears within 24 to 48 hours of the first symptom. After a couple of days, the blister will burst and ooze with fluid. A scab will then form over the blister. (4)

Learn More About Signs and Symptoms of Cold Sores

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

You may mistake a cold sore for a canker sore, but these bumps have key differences, including their:

Appearance Canker sores are painful red or white bumps that typically form on the gums, inside the lips or cheek, or on the tongue. Unlike cold sores, they don’t blister or scab.

Contagiousness Unlike cold sores, canker sores aren’t caused by herpes and they aren’t contagious. So while it is possible to spread a cold sore to someone through kissing or sharing eating utensils, this isn’t the case with a canker sore. (5)

Cause Cold sores are commonly caused by HSV-1, and yet the cause of a canker sore is unknown. Factors that may contribute to a canker sore include a family history of canker sores, injury to the mouth, a weak immune system, or a vitamin deficiency. (5)

Learn More About the Difference Between Cold Sores and Canker Sores

Causes and Risk Factors of Cold Sores

Cold sores are caused by the herpes simplex virus (HSV). (1)

There are two types of HSV. Most cold sores are caused by type 1 (HSV-1). Type 2 (HSV-2) usually affects the genital area, but it can also cause cold sores around the mouth, says Dr. Arthur. (2)

This can happen after oral sex with someone who has genital herpes, or if you kiss someone who has HSV-2 cold sores around their mouth.

Upward of 90 percent of adults have the virus that causes a cold sore. (1) Roughly a quarter of these adults were infected by first grade, some others later in childhood, and the rest as adults.

Cold sores can be found on or around the lips, but some people also get sores on the cheek, or around the nose and the eyes. (1)

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Is It a Canker Sore or Something Else?

Once you’re infected with HSV-1, the virus travels to your nerves and stays in your body for life. The virus can lie inactive or dormant, so some people infected with HSV-1 never get a cold sore. In fact, some people don’t even know that they’re infected with the virus because they never have symptoms. (4)

Unfortunately, you can still pass the virus to others even when you don’t have visible symptoms of a cold sore. (6)

Cold sores occur when the virus awakens in the body.

Certain factors can trigger this awakening and cause an outbreak. (7)

These triggers include:

  • A viral infection or fever
  • Hormonal changes
  • Stress
  • Fatigue
  • Exposure to sun and wind
  • Changes in the immune system
  • Cosmetic procedures like microdermabrasion and facial laser treatments
  • Facial surgeries

Sometimes, a cold sore has unknown triggers.

Learn More About Causes of Cold Sores: Common Risk Factors and More

How Are Cold Sores Diagnosed?

A cold sore is treatable at home, so most people don’t need to see a doctor. Under certain conditions, however, a severe cold sore may require a visit to your family doctor or a dermatologist. (3)

Doctors usually can diagnose a cold sore by looking at the lesion. More rarely, your doctor may take a fluid sample from the cold sore to see if you have HSV. (3)

Prognosis of Cold Sores

There’s no cure for cold sores, nor is there a cure for the virus that causes a cold sore. (1) Once you’re infected, the virus stays in your body for life.

But even with recurrence, in healthy individuals the prognosis for a cold sore is typically good and complications are rare, unless you are immunocompromised.

Duration of Cold Sores

A first-time cold sore typically lasts 10 to 14 days. Later outbreaks might last this long, or they might heal sooner, perhaps even within five days. (4)

Treatment and Medication Options for Cold Sores

A number of treatments are helpful for cold sore outbreaks.

Medication Options

Because cold sores are caused by a virus, you could try over-the-counter antiviral medication like docosanol (Abreva) at the first sign of an outbreak. However, data is conflicting about its effectiveness.

Additionally, you could use an over-the-counter oral pain reliever, such as lidocaine, benzocaine (Orajel), dibucaine, or benzyl alcohol, to relieve cold sore pain and inflammation. (3) Apply ointments and creams directly to the cold sore as directed. Other pain relief options include a cool compress, or taking ibuprofen (Advil), aspirin, or acetaminophen (Tylenol). (2,3)

If a cold sore doesn’t respond to over-the-counter treatment, ask your doctor about a prescription antiviral to shorten the duration of an outbreak. If you have frequent outbreaks, you may need an antiviral daily to suppress the virus and control symptoms. (8) You can also ask about the topical therapy penciclovir (Denavir), which can be used to shorten the duration of a cold sore outbreak. (9) To use, you typically apply it every two hours while awake, for four days.

Also, if your outbreaks are frequent or severe, you could discuss with your doctor whether L-lysine supplementation or a low-arginine diet might be appropriate for you to try. However, do not attempt these treatments without the counsel of a doctor because they can cause serious health effects.

Alternative and Complementary Therapies

Other tips to reduce an outbreak include getting plenty of rest, managing stress, and wearing sunscreen to protect against strong sun exposure. (7)

Alternative therapies may also relieve a cold sore, though more research is needed. According to a past study, researchers found that a combination of rhubarb and sage had the same healing effect as acyclovir (Zovirax), a topical antiviral commonly used to treat herpes infections. (10)

Additionally, research from 2018 found that a 3 percent propolis ointment applied to areas affected by HSV-1 reduced symptoms of infection by three to four days. Propolis is a compound produced by bees. Participants applied the ointment four to five times a day for 10 days. (11)

Learn More About Treatment for Cold Sores: Medication, Complementary Therapies, and More

Prevention of Cold Sores

Cold sores are highly contagious, but you can protect yourself. Since the virus can spread through close personal contact, it’s important that you don’t share personal items with anyone — especially during an outbreak. (12)

Personal items include clothes, makeup, razors, and towels. You should also avoid sharing food and drinks with others.

Keep in mind, too, cold sores can spread to other parts of the body. So if you have an outbreak, avoid touching your cold sore with your hands. After applying creams or ointments over a cold sore, wash your hands immediately with warm soap and water. (1)

If you’re prone to cold sores in the summer, sunlight might be a trigger. Wear a moisturizing lip balm with SPF protection to help prevent an outbreak. (7)

Complications of Cold Sores

See a doctor if you have cold sore complications. This includes a cold sore that spreads to different parts of your body, such as your eyes or fingers. Additionally, see a doctor if you are pregnant or have a weak immune system. (2)

People who are immunocompromised — for example, they have a weakened immune system due to HIV or medications following organ transplantation — can develop severe outbreaks and have frequent episodes of cold sores, says Arthur.

If your body is unable to fight the virus, it can also spread to your spinal cord and brain. (1) If you have eczema, there’s also the risk of cold sores spreading across your body. (1)

Research and Statistics: Who Has Cold Sores?

It’s estimated that over half of Americans between ages 14 and 49 have the virus that causes cold sores. Many people get the virus in childhood. (7)

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How Do I Know if I Have Herpes or Something Else?

Some people with the virus never have an outbreak, whereas others have frequent outbreaks throughout their life. Fortunately, cold sores occur less often with age. Outbreaks tend to slow down after the age of 35. (7)

Related Conditions and Causes of Cold Sores

Cold sores have been associated with other conditions and health problems. For example, if you have a weakened immune system, certain illnesses might trigger an outbreak. These illnesses include: (12)

  • Common cold
  • Flu
  • Pneumonia
  • Urinary tract infection
  • Cancer

Skin conditions like eczema and psoriasis also put you at risk of an outbreak. And because fluctuating hormone levels can trigger outbreaks, a cold sore might develop while you’re pregnant or menstruating. (12)

Resources We Love

Favorite Resources for Essential Cold Sore Information

American Academy of Dermatology (AAD)

The AAD provides a comprehensive overview of cold sores ranging from symptoms to self-care. There’s an information section for parents, as well as information on public health programs. Use the “find a dermatology” tool to locate a doctor in your area.

Cleveland Clinic

This is another helpful tool to find useful information related to cold sores. The Cleveland Clinic doesn’t only offer advice on treatments, but also advice on prevention and living with cold sores. Use the online tool to chat with a representative or schedule an appointment.

Mayo Clinic

The Mayo Clinic provides straightforward information about cold sores. The site features general information such as symptoms, treatments, and prevention. You’ll also find guidelines on when to see a doctor, and tips on how to prepare for an appointment.


MedlinePlus offers a wealth of resources for cold sores. You’ll find general information for symptoms and treatments, as well as links to clinical trials, journal articles, and patient handouts.

Favorite Online Support Network


Support groups are an excellent way to get advice and connect with those who understand your condition. Join the Drugs.com support group to ask questions and find the latest information related to oral herpes.

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