Everything you need to know about cold sores

Fever blisters can be treated with prescription antiviral medications either applied as topical creams or taken orally. See a doctor if your cold sores persist longer than a few weeks, you develop a high fever, or you notice eye irritation.

Fever Blisters & Canker Sores

Both fever blisters and canker sores are common across all ages and can be painful. However, they are separate conditions with different causes. Read further to learn how to tell them apart and find out which treatments might help ease the pain.

Fever Blisters (also known as cold sores) are painful fluid-filled sores that form on the outside of the mouth around the lips. Fever blisters are very contagious.

Canker Sores are painful white or yellow sores that only form inside the mouth, usually on the insides of the cheeks or lips or on the tongue. Canker sores (also called aphthous ulcers) are not contagious.

Causes

Fever Blisters are caused by an infection with the herpes simplex virus, usually type 1, or HSV-1. It is estimated that nearly 90 percent of U.S. adults have been infected with the virus, although many people with the infection do not ever show symptoms. The virus generally resides in the nerve cells where it may periodically reactivate, traveling to the skin and causing recurring fever blisters.

Canker Sores do not have a known cause. They may be triggered by an injury, stress, smoking, or deficiencies in folic acid, iron, or vitamin B12.

Symptoms

Symptoms of fever blisters:

• Fluid-filled blisters on the outside of the mouth around the lips.
• Burning or tingling sensation at the site where the blisters will appear.
• And sometimes, fever, fatigue, or swelling of the lymph nodes, similar to other viral infections.

Symptoms of canker sores:

• A round white or yellow sore with a red border inside the mouth, usually on the inside of the lips or cheeks or on the tongue.
• A burning or tingling sensation may occur in the mouth prior to the formation of the sore.

Diagnosis

The main way to tell the difference between a fever blister and a canker sore is by location. Fever blisters occur outside the mouth, generally around the border of the lips. Canker sores occur inside the mouth.

They also differ in appearance: Fever blisters are patches of several small fluid-filled blisters, while canker sores are usually single round white or yellow sores with a red border.

Collection of small, fluid-filled blisters

Usually a single round white or yellow sore with a red border

Treatment

Typically, both types of sores go away on their own and treatment is not usually required. There is no known treatment that can permanently cure fever blisters or canker sores and prevent them from recurring. Treatment focuses on minimizing the pain and speeding recovery time.

Fever blisters can be treated with prescription antiviral medications either applied as topical creams or taken orally. See a doctor if your cold sores persist longer than a few weeks, you develop a high fever, or you notice eye irritation.

Canker Sores can be treated with over-the-counter (non-prescription) gels to numb the pain. Avoiding spicy or abrasive foods may also help. Rinsing the mouth with over-the-counter antiseptic medications may help prevent infection of the sore and speed healing.

See a doctor if you have frequently recurring canker sores or if the sores are severe enough to make eating or drinking difficult. If you have recurring canker sores as a result of a vitamin deficiency, treating the deficiency may reduce their frequency.

Helpful Tips

Both fever blisters and canker sores can have triggers that produce flare ups. Try to identify and then avoid triggers so your flare ups become less frequent.

Tips for Fever Blisters

• Sun exposure may sometimes trigger outbreaks of fever blisters. If you have recurring blisters, using sunscreen may help reduce their frequency.
• Fever blisters are contagious. Avoid kissing, sharing eating utensils, cups, water bottles, or other items if you are experiencing symptoms.
• Be aware that in young children, fever blisters can cause loss of appetite, drooling, and fever that can last for several days.
• Talk to your doctor or your child’s pediatrician if symptoms are severe or recur frequently.

Tips for Canker Sores

• If you regularly get canker sores, talk to your doctor about testing for food allergies, as allergic reactions can sometimes trigger canker sore outbreaks.

Additional Resources

• MedlinePlus (Fever Blisters)
  Information about oral herpes (the infection that causes cold sores) from the NIH National Library of Medicine.
• MedlinePlus (Canker Sores)
  Information about canker sores from the NIH National Library of Medicine.

Everything you need to know about cold sores

Cold sores are small, blister-like lesions that tend to form on the lips, chin, or cheeks, or in the nostrils. They less frequently appear on the gums or the roof of the mouth.

Cold sores usually cause pain, a burning sensation, or itching before they burst and crust over. People sometimes call them fever blisters.

The most common cause of cold sores is the herpes simplex virus type 1 (HSV-1). Other times, these sores result from an infection with a different strain, called herpes simplex virus type 2 (HSV-2).

In the United States, 48.1% of all people aged 14–49 years have HSV-1, making them more susceptible to cold sores.

There is no way to cure or prevent these sores, but a person can take steps to reduce the frequency and duration of outbreaks.

The viral strains that cause cold sores, usually HSV-1 and less often HSV-2, are highly contagious and transmit easily during close contact, such as sexual contact.

After the virus enters the body, a person may have:

• flu-like symptoms
• sores in or around their mouth or in their nostrils
• sores around the genital area, in some cases

It is possible for oral herpes sores, or cold sores, to develop around the genitals if transmission happens during oral sex.

A cold sore outbreak typically lasts 1–2 weeks , without treatment, before the body’s immune system suppresses the virus.

The virus does not leave the body, and though it remains inactive most of the time, it can periodically reactivate to cause cold sores.

Most people with oral herpes do not realize it until they experience cold sores or other symptoms. Some people have just one outbreak and no reoccurrence because the virus stays dormant.

Others may have frequent outbreaks that continue for many years.

Some people with oral herpes have no symptoms, and others only experience them after the first exposure to the virus.

Still, at least 25% of people with oral herpes experience reoccurring outbreaks. In this case, cold sores often appear in the same locations each time.

Initial symptoms of an HSV-1 infection may appear 2–20 days after exposure to the virus and can include:

• lesions on the tongue, mouth, chin, cheeks, or in the nostrils
• mouth or tongue pain
• lip swelling
• difficulty swallowing
• a sore throat
• swollen lymph nodes
• a high body temperature
• headaches
• dehydration
• nausea

There may also be an infection of the mouth and gums, known as gingivostomatitis. This lasts for 1–2 weeks and does not reoccur.

Also, in adults, an infection of the throat and tonsils called pharyngotonsillitis may develop with the initial oral herpes infection.

A cold sore develops in several stages when it reoccurs.

• A tingling, itching, or burning sensation around the mouth often indicates the start of an outbreak.
• Painful, fluid-filled sores appear, usually around the mouth.
• The sores break and produce fluid.
• A yellow crust forms on the sores.
• The crust comes off, revealing pink skin that heals in 3–4 days.

Without treatment, most cold sores disappear within 1–2 weeks and do not leave a scar.

People with reoccurring outbreaks can manage them at home by recognizing the signs and using medication.

• Symptoms are severe.
• A cold sore does not start to heal within 10 days.
• The gums swell.
• The person has a weakened immune system.
• Other symptoms are causing concern.

A doctor can usually diagnose the issue by considering the symptoms and making a visual examination, but in some cases — such as if the person has a weakened immune system — they may also order a blood test or take a sample of a sore’s fluid for testing.

Some factors that can weaken the immune system include HIV, medications following an organ transplant, some types of cancer, and some cancer treatment.

Most cold sore outbreaks resolve in 1–2 weeks without treatment.

However, some over-the-counter or prescription medications can shorten an outbreak’s duration and reduce any discomfort or pain, though these do not remove the virus from the body.

In most cases, it is best to use treatments as soon as the first signs of an outbreak appear.

Antiviral creams

Over-the-counter antiviral creams can shorten the duration of an outbreak. Most creams, such as Zovirax and Soothelip, contain acyclovir or penciclovir.

A person should apply the cream to the affected area every 2–3 hours for 5 days.

Oral antiviral medications

Some examples of antiviral medications that a person can take by mouth include:

• valacyclovir (Valtrex)
• acyclovir (Zovirax)
• famciclovir (Famvir)

A doctor may prescribe one of these medications if a person has a weakened immune system or otherwise has regular outbreaks.

A person takes it once or twice a day.

These medications can shorten the duration of an outbreak and may keep them from reoccurring.

Pain relief

Over-the-counter options contain an analgesic such as benzocaine or lidocaine. They do not speed the healing process, but they can reduce discomfort.

Some pain relief medications for cold sores include:

People should dab these ointments, creams, or gels onto the sores with a Q-tip, and it is important not to share these products.

If a person applies the medication with a finger instead, they should wash their hands before and after.

Some alternate options include medications such as ibuprofen (Advil) or acetaminophen (Tylenol).

Home remedies

Some people find that the following home care techniques relieve cold sore symptoms:

• applying cold, soaked tea bags to the area every hour
• dabbing the area with diluted geranium, lavender, or tea tree oil
• using petroleum jelly to keep the skin moist, preventing cracking

There is no scientific evidence that these remedies work or are safe.

Rarely, oral herpes can lead to complications, especially in people with weakened immune systems.

Possible complications include:

• dehydration, if pain from the sores makes drinking difficult
• herpetic whitlow, a painful infection that can occur through a cut on the skin and cause blisters, usually on the fingers
• herpetic keratoconjunctivitis, a secondary infection that can cause eye swelling and irritation, sores on the eyelids, and, without treatment, vision loss
• encephalitis, or swelling of the brain, which may occur if the infection spreads

Encephalitis can be life threatening.

When sores are present, try to:

• Avoid kissing and other skin-to-skin contact involving the affected area.
• Use a dental dam or condom during oral sex.
• Avoid sharing personal items, such as towels and lip balm.
• Follow correct handwashing techniques.
• Avoid touching areas where sores can develop, such as the eyes, mouth, nose, and genitals.
• If touching the sores is necessary, wash the hands with soap and warm water before and after.

Cold sores can be a painful and disruptive symptom of oral herpes.

Many people do not experience complications and can manage outbreaks at home with over-the-counter or prescription treatment.

Anyone with a weakened immune system should let a doctor know if they have cold sores or any other oral herpes symptoms.

Recognizing the early indications of an outbreak and using treatment right away can help. Without treatment, cold sores often disappear within 1–2 weeks .

Last medically reviewed on September 23, 2020

• Dermatology
• Infectious Diseases / Bacteria / Viruses
• Sexual Health / STDs

How we reviewed this article:

Medical News Today has strict sourcing guidelines and draws only from peer-reviewed studies, academic research institutions, and medical journals and associations. We avoid using tertiary references. We link primary sources — including studies, scientific references, and statistics — within each article and also list them in the resources section at the bottom of our articles. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.

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Medically reviewed by Debra Sullivan, Ph.D., MSN, R.N., CNE, COI — By Adam Felman — Updated on Sep 25, 2020

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© 2004-2023 Healthline Media UK Ltd, Brighton, UK, a Red Ventures Company. All rights reserved. MNT is the registered trade mark of Healthline Media. Any medical information published on this website is not intended as a substitute for informed medical advice and you should not take any action before consulting with a healthcare professional. See additional information.