Cold sores, alternatively called fever blisters, on the lips are small, blister-like lesions. They may also form on the chin, cheeks, or in the nostrils, as well as the gums or the roof of the mouth.

Cold sores usually cause pain, a burning sensation, or itching before they burst and crust over.

They usually develop after contracting the herpes simplex virus (HSV). There are two types of HSV, which include HSV-1 and HSV-2.

HSV-1 is spread through oral contact and can result in cold sores in and around the mouth. It can also cause genital herpes.

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Cold sores are caused by HSV-1. It is a very common virus, affecting nearly 90% of the US adult population.

HSV-1 is often transmitted through oral contact, such as kissing. It is possible to transmit HSV-1 to the genitals during oral sex, which can result in genital herpes.

Once a person contracts HSV, it does not leave the body. Instead, it usually remains inactive, but can periodically reactivate, resulting in a cold sore.

Some people with HSV-1 do not experience any symptoms. However, if signs and symptoms do appear, a person may experience flu-like symptoms, such as fever, muscle aches, and swollen lymph nodes in the neck once the virus enters the body. These symptoms appear between 2 and 20 days after contracting the virus.

The skin may itch, burn, or tingle before the cold sore appears. Once the cold sore develops, a person will have a painful, fluid-filled blister on the lips or around the mouth. They can also appear on the face or tongue.

These sores last from 7 to 10 days before bursting and crusting over. Without treatment, most cold sores disappear within 1 to 2 weeks and do not leave a scar.

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

A doctor can usually diagnose a cold sore based on the symptoms and by 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 the sore’s fluid for testing.

A person can consult a doctor if:

  • 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.

Most cold sore outbreaks resolve 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 to 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 recurring.

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:

  • Orajel
  • Blistex
  • Cymex
  • Anbesol

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 to 2 weeks.