Cold sores are fluid filled blisters that appear on the lips and around the mouth. They develop in response to a common viral infection. Generally, a cold sore is contagious for around 15 days.

The first sign of a developing cold sore tends to be a burning or tingling sensation in the area. This may be 1–2 days before the onset of visible blisters.

By this point, it may already be contagious.

The cold sore will appear as a cluster of blisters on the surface of the skin. Typically, these blisters will burst, resulting in an open and painful sore. A scab then forms over the wound.

Once the scab falls off and the skin heals, the cold sore is no longer contagious.

The entire process usually takes around 7–12 days, though the cold sores may last for up to 15 days.

In this article, we explore how people contract and transmit the cold sore virus. We also provide information on cold sore symptoms, prevention tips, and treatment options.

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Cold sores may be contagious for up to 15 days.

The herpes simplex virus type 1 (HSV-1) is what causes cold sores.

According to the National Institutes of Health (NIH), in the United States, HSV-1 infects more than 50% of people by the time they reach their 20s. Most people contract it during childhood.

HSV-1 is highly contagious. People who have it can transmit it to another person by kissing or sharing utensils, towels, or other personal care items. The virus can then enter the body through a small cut in the skin.

Once a person has HSV-1 in their system, it is there for life, as there is currently no cure. The virus can remain dormant for long periods of time but may reactivate at any point.

In some cases, however, the virus may never become active. Many people with the virus do not develop cold sores.

It is possible for a person to transmit HSV-1 to others when the virus is inactive. However, HSV-1 is much more likely to be contagious when cold sores are present.

There are many triggers that can cause the virus to reactivate. They may include:

  • dental work
  • emotional distress
  • fever
  • hormonal changes, such as from menstruation
  • infection
  • injury
  • stress
  • exposure to sunlight
  • surgery

People who develop cold sores may experience them less frequently as they age. According to the American Academy of Dermatology, HSV-1 tends to reactivate less often in people over the age of 35.

Reactivation also tends to be more common in the first year after the initial outbreak.

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A person with HSV-1 may experience headaches, fever, and flu-like symptoms.

Most people contract HSV-1 during childhood. However, some contract the virus later in life.

When someone initially becomes infected, they may experience the following symptoms:

Symptoms typically last for up to 2 weeks, though some people may not develop any symptoms at all.

Reactivation symptoms and stages

Many people experience a burning, itching, or tingling sensation on or around the lips 1–2 days before a cold sore appears. This is called the prodrome stage.

During the next stage, fluid filled blisters will develop. Around a third of people experience cold sores at the same location each time.

Within 48 hours, the blisters tend to burst and leak fluid. This stage can be painful and may last for around 3 days. This is when the cold sores may be most contagious.

In the final stage, a scab forms over the wound. The scab may crack or bleed until it finally clears up. Once the skin is clear of the cold sore, it is no longer contagious.

Most cold sore outbreaks do not require a visit to the doctor. They typically clear up on their own within 7–12 days.

Trying home treatments during this time can reduce discomfort. They can also prevent transmission to other parts of the body, and to other people.

Home remedies

Some home remedies include:

  • Trying topical antiviral medications: Some antiviral cold sore medications, such as docosanol (Abreva), are available over the counter.
  • Applying sunscreen: Protecting cold sores from the sun helps prevent further skin damage. Ideally, people should apply a lip balm with a sun protection factor (SPF) of 30 or higher.
  • Taking pain relief medications: Taking over-the-counter pain relievers, such as ibuprofen (Advil, Motrin) or acetaminophen (Tylenol), may reduce discomfort.
  • Applying ice: Applying an ice pack to the area may help bring down pain and swelling. People should wrap ice packs in a clean towel first. Applying ice directly to the skin can cause more damage.
  • Trying petroleum jelly: Applying this to cold sores may aid the healing process.
  • Making dietary changes: Eating acidic, salty, and spicy foods can cause burning pain if they touch the sores. Therefore, it can be helpful to avoid these foods until the sores heal.

Medical treatments

People should see their doctor if cold sores are severe or persist beyond 15 days. A doctor may recommend:

  • prescription antiviral medication in the form of topical cream or oral medication
  • intravenous antiviral medications (for severe outbreaks)
  • pain relief medications

People who experience regular outbreaks may need to take prescription medication to keep their symptoms under control.

A person should also see a doctor for cold sore treatment if they:

  • develop numerous sores
  • develop sores near the eyes or on the hands or genitals
  • experience severe pain with the sores
  • are pregnant
  • have atopic dermatitis
  • have cancer and are undergoing chemotherapy treatment
  • have HIV, AIDS, or another condition that weakens the immune system
  • take an immunosuppressant medication

In these cases, the cold sores may not go away on their own. Medical treatment can also help prevent complications.

The following tips can help limit the spread of HSV-1:

  • Avoid kissing other people while the sores are active.
  • Avoid engaging in oral sex and other intimate contact until the sores have healed.
  • Do not share personal care products, such as razors, lip balms, and towels, with other people.
  • Do not share utensils, drinks, or foods.
  • Refrain from touching the sores unless necessary, such as when applying cream.

Wash the hands immediately after touching a cold sore and regularly throughout the day.

When cold sores are present, people should take extra precautions during contact with people who have weaker immune systems. This includes children and newborn babies, whose immune systems have had less time to develop.

People can also take measures to reduce their chance of experiencing a cold sore outbreak. These include:

  • wearing sunscreen or lip balm with an SPF of 30+ every day
  • practicing yoga or meditation to help reduce stress
  • getting enough sleep each night
  • taking any prescribed antiviral medications at the first sign of an outbreak

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A doctor may prescribe medication to treat an outbreak of cold sores.

There is currently no cure for cold sores. This means that once a person contracts HSV-1, they will have it for life.

However, not everyone who has the virus will develop cold sores.

People who are prone to cold sores can try to reduce their exposure to potential triggers. These include stress, sunlight, and infections.

Taking prescription medication may be helpful for those who experience regular outbreaks.

HSV-1, the virus that causes cold sores, is very common among adults in the U.S. Most people who have it contract the virus in childhood.

Cold sores are highly contagious from the time the first symptom appears. This is usually 1–2 days before the sore becomes visible. Sores remain highly contagious until the skin completely heals. This can take up to 15 days.

During an outbreak, people should be careful not to transmit the virus to others.

Trying home remedies can help relieve the symptoms. If these are not effective, medical treatments can reduce pain and speed up healing.

Those who have concerns about cold sores or other mouth lesions should see their doctor.