Cold sores: Causes, symptoms, and treatment

Cold sores are small sores, or blister-like lesions, that appear on the lips, chin, cheeks, inside the nostrils, and less frequently on the gums or the roof of the mouth.

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

They are often called fever blisters. The most common cause of cold sores is the herpes simplex type 1 (HSV-1), but sometimes the herpes simplex type 2 (HSV-2) can cause it.

In the United States (U.S.), between 50 and 80 percent of people have oral herpes, making them potentially susceptible to cold sores.

There is no way to cure or prevent cold sores, but steps can be taken to reduce their frequency and duration.

Fast facts on cold sores

Here are some key points about cold sores. More detail is in the main article.

Cold sores are tiny blisters that develop on the lips or around the mouth.

The herpes simplex virus strain HSV-1 normally causes them.

They usually clear within 7 to 10 days without treatment.

The virus is highly contagious and can be passed on through close direct contact.

After someone has contracted the “cold sore virus”, it remains inactive for most of the time, but triggers such as fatigue and injury can activate it.


[Cold sores]
Cold sores appear on the face and around the mouth.

The herpes simplex virus (HSV) causes cold sores. HSV-1 and HSV-2 are highly contagious viruses that can be transmitted easily as a result of close contact.

After entering the body, the virus remains inactive most of the time, but, if a trigger activates the virus, a cold sore can develop.

One person may have just one outbreak and no recurrence, while others may have two or three outbreaks each year.

Some people may carry the virus and never have an outbreak because it remains dormant.

Infection with HSV-2 may result from oral sex acts with a person who has genital herpes.


Many people have the herpes simplex virus but no symptoms. They will only know they are infected if cold sores appear.

The first time a cold sore appears, as part of a primary infection, it may be severe.

After this, cold sores are considered a symptom of HSV-1 and 2. They remain as the only recurring sign that the virus is present in the body.

In most cases, there are no other detectable signs or symptoms of a herpes infection.

Severe symptoms are more likely to affect young children, as they have not yet had time to build up antibodies as a defense.

Symptoms can include:

lesions, blisters, or ulcers on the tongue or mouth

mouth or tongue pain

lip swelling

possible swallowing difficulties

sore throat

swollen glands

high body temperature




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

Pharyngotonsillitis, an infection of the throat and tonsils, may occur when the primary infection affects adults.

[Cold sores HSV]
The herpes simplex virus causes cold sores.

A cold sore will develop in several stages when it recurs.

A tingling, itching or burning sensation around the mouth often indicates the start of a cold-sore outbreak. Fluid-filled sores, often on the edges of the lower lip, tend to follow this. Glands may start to swell.

The sores often appear in the same place each time. Pain and irritation develop alongside the cold sore.

The sores break and ooze.

A yellow crust forms on top of the sores and scabs off to uncover pink skin that heals without scarring.

Most cold sores disappear within a week or two.


Those with previous experience of a cold sore outbreak will easily recognize a recurrence.

People who suspect that they or their child may have a primary infection, especially if the sore has not healed within a week or so, should see their doctor.

The signs and symptoms are usually clear enough for a doctor to make a diagnosis, but they may also order a blood test.

In some cases, the doctor may take a sample of the fluid scraped from the cold sore to detect the presence of the virus.

This is usually done only on patients with weak immune systems, such as those undergoing chemotherapy, or people with HIV or AIDS.


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