Cold sores are skin lesions that often turn to tender blisters. Although there is no cure for the virus that causes them, cold sores will go away on their own over time, and various medicines can treat the symptoms.

A cold sore under the nose is a common complaint. Cold sores are harmless and usually go away on their own within 1–2 weeks, but they can be bothersome.

In this article, we explain what cold sores are and what causes them. We also look at possible complications and how to treat and prevent them.

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Cold sores consist of small lesions, or bumps, that appear on the skin. A person might notice a single sore or a cluster of them.

They tend to develop on the face — typically around the mouth, on the lips, or underneath the nose.

Cold sores usually start out as a discolored or white bump, which might resemble a pimple. The bump will usually develop into one or a group of tender, fluid-filled blisters. These might be red or darker than the surrounding skin, or they might be yellow or white.

Over the course of a couple of weeks, the blisters will usually get bigger and break open. When this happens, the fluid oozes out. A crust then forms before the sore eventually heals and disappears.

The herpes simplex virus type 1 (HSV-1) causes cold sores. HSV-1 is highly contagious and spreads in saliva. It is also very common, and more than half of all people in the United States will have contracted it by the time they reach their 20s.

Once someone has caught the virus, it stays in their body for the rest of their life. Sometimes, a person is asymptomatic, which means that they do not have any symptoms.

For some people, the virus will reactivate, or “wake up,” and cause a cold sore every so often.

Many factors can prompt the virus to reactivate. Triggers vary among individuals, but they may include illness, injury, stress, and sunshine.

The symptoms of HSV-1 tend to be more severe in people who have recently caught the virus than in those who have had it for some time.

People usually get the infection as children, but it can happen to adults, too.

Not everyone who catches the virus will develop symptoms, but those who do might experience the following:

  • a burning sensation in the mouth
  • painful sores on the face, including on the tongue, gums, lips, throat, and face
  • a sore throat and pain when swallowing
  • fever
  • headaches
  • nausea
  • swollen glands

The symptoms usually last for 1–2 weeks and then go away on their own.

Once someone has the virus, it moves into their nerves and lies dormant, or goes to sleep. In some people, it reactivates, or wakes up, every so often.

When this happens, people develop a cold sore. However, the symptoms are not usually as severe as they were the first time. For example, a person is unlikely to experience fever and swollen glands.

When someone gets a cold sore, the symptoms tend to come in stages:

  • Warning signs: A burning, itching, or tingling sensation on the skin is usually the first sign of a cold sore. Some people describe it as a stinging or throbbing feeling.
  • After 1–2 days: The person might develop one or more painful, fluid-filled blisters. These can appear anywhere on the face, including under the nose.
  • About 48 hours later: At this stage, the blisters break open. When this happens, the fluid oozes out and crusts over to form scabs.
  • Within 1–2 weeks: The sore will usually heal on its own.

Anyone can catch the virus that causes cold sores. It spreads through saliva, so people can catch it from having close physical contact with others, sharing items such as eating utensils or lip balm, or drinking from the same bottle or glass.

Although the virus can still spread from a person with no symptoms, it is most contagious when they have a cold sore.

People who have health conditions that affect their immune system may be at higher risk of cold sores. That includes people who:

In most cases, cold sores under the nose are not a cause for concern. They will go away on their own.

However, in rare cases, HSV-1 can lead to complications, such as encephalitis, which is inflammation of the brain, or keratitis, which is inflammation of the cornea in the eye.

These complications tend to affect people with a severe infection and weakened immune system.

Cold sores underneath the nose will get better by themselves. However, antiviral medications can ease the symptoms and reduce the time that the blisters take to heal.

According to the World Health Organization (WHO), the most effective medicines for cold sores are:

  • acyclovir (Zovirax)
  • famciclovir (generic only)
  • valacyclovir (Valtrex)

They are available over the counter (OTC) as creams and ointments. Prescription-strength versions are also available from doctors, who usually reserve them for people with a severe infection.

It is important to remember that these medications help with the symptoms but will not clear the virus.

Canker sores and cold sores can look similar, but they are different.

Cold sores tend to develop on the face, usually around the mouth and in the space between the lips and nose.

Canker sores develop inside the mouth, usually inside the cheek, under the tongue, or in the back of the throat. They are small, round sores with a red edge and gray center. They can be painful.

Viral infections, stress, food allergies, or a lack of vitamins and minerals can cause canker sores. Hormonal changes and menstrual periods can also play a role.

Canker sores will usually go away on their own.

HSV-1 spreads through saliva. People can prevent infection by:

  • avoiding kissing someone with a cold sore
  • avoiding sharing cups, cutlery, or straws with others
  • refraining from sharing lip balm or lipstick

Once someone has caught HSV-1, they can minimize the likelihood of cold sores by trying to avoid their triggers. That might mean using relaxation techniques to reduce stress or regularly applying sunblock before exposure to sunshine.

The HSV-1 virus can cause cold sores underneath the nose. Cold sores are painful, fluid-filled blisters on the face.

In most cases, cold sores are harmless and will go away on their own. OTC antiviral medicines that can ease the symptoms and reduce the healing time are available.

In rare cases, HSV-1 infection can lead to complications, including brain and eye inflammation.