why do i get cold sores in my mouth ? Causes of cold sore, Symptoms and complications, triggering factors, Treatment and prevention

The cold sore, also known as wild fire, is caused by a virus. Cold sores usually appear around the mouth and on the lips. They are highly contagious, but not dangerous.

About 60% of the population had cold sores at some point. People who make cold sores have 2 or 3 episodes per year, on average, but this figure can vary greatly from one person to another.

Causes of cold sore:

The most commonly responsible virus for cold sores is herpes simplex virus type 1, a cousin of herpes simplex virus type 2. However, in a minority of cases, herpes simplex virus type 2 may also cause cold sores. Nearly 80% of the population in North America is the carrier of the herpes simplex virus of type 1 dormant (inactive) that lives permanently in the organism.

The virus usually resides in a State of dormancy within the nerve cells of the body. The immune system is normally able to keep the virus in idle condition. However, when an infected person is exposed to a “triggering factor” or if his or her immune system is weakened, the virus multiplies rapidly, then spreads along the nerve cells to emerge on the skin, usually on Lips. This phenomenon results in a characteristic sensation of tingling and the subsequent appearance of clusters of vesicles.

Specific triggering factors include:

  • cold weather;
  • fatigue
  • a fever, such as that caused by intestinal flu or other infection;
  • menstruation;
  • mental or physical tension
  • physical irritation of the lips (e.g. following a visit to the dentist);
  • Sun or sunburn.

You can contract the virus if you come into direct contact with the cold sore or the liquid it contains, carrying a large number of particles from the virus. Simply shake the hand of a person who has touched his vesicles. Or use a toothbrush, mug, Cookware, washcloth, towel, lipstick, or any other personal item contaminated with the cold sore liquid. Once the vesicles are no longer painful or form a crust, the person is no longer contagious.

Symptoms and complications

People with cold sores may have an unusual sensation around the lips within 24 hours prior to the onset of vesicles, including tingling, burning, pain or numbness. It is a prodrome, or precursor sign, of the onset of cold sores at this place. Redness appears on the skin, then vesicles form. For a few days, the latter let out a clear liquid that will then dry to form a yellow crust in about 3 to 5 days. The phenomenon usually comes with a little pain during the first few days after the onset of cold sores, but the pain often disappears during the formation of the crust. Complete healing takes 10 to 14 days.

This condition typically causes an amalgam of lesions, or vesicles, at a point around the lips. Other areas that the lips can also be touched, for example the inside of the mouth, around the nostrils or even the eyes. The virus can spread to other parts of your body if you touch the vesicles and then you touch elsewhere. Cold sores located in the mouth can cause problems and harm you when you talk or eat. If the virus contaminates the eye, it can damage the surface and lead to loss of sight. In very rare cases, it can contaminate the brain and cause viral meningitis or encephalitis. Herpes Simplex Type 1, the virus that causes cold sores, can also spread to the genitals through oral sex, resulting in genital herpes.

The herpes simplex virus of type 1 never disappears altogether, so the cold sores can reappear later if there is a new triggering factor. Most cold sores don’t leave scars. However, if an open vesicle is infected with a bacterium, or if the lesions tend to reappear in the same place, a scar may result. People with weakened immune systems tend to get more cold sores and heal less quickly.


Cold sores have clear and obvious symptoms, so there is no need to carry out a battery of tests. In any case, it is rare that it is necessary to consult a doctor. However, it is better to go see a doctor if you notice any redness or pain in the eye, a fever greater than 38 °c (100 °f) or a thick yellowish white liquid flowing from the vesicles. It could be a bacterial infection. The doctor can check if the fluid flowing from the vesicles contains bacteria.

A doctor should also be consulted if the lesions last longer than 14 days, if they occur more than 6 times a year or if the cold sore is manifested at the same time as a disease that weakens the immune system.

Treatment and prevention

There is no known way to cure cold sores. Wildfires disappear on their own but some medications may be useful to prevent the progression of wild fires and treat the pain associated with wildfires.

Among the medicines used to treat cold sores, we find:

acyclovir *, an antiviral drug, can be applied in the form of ointment, 4 or 5 times a day;

a combination of acyclovir and hydrocortisone may be prescribed in the form of cream. This medicine can stop the progression of the disease (ulcerations) if used at the stage of prodrome. It can reduce the healing time of ulcerous lesions by 1.4 day and the duration of pain by one day;

acyclovir, famciclovir or valacyclovir can be taken orally to prevent the onset of a cold sore. These antiviral medications may be beneficial if taken within one hour of the onset of symptoms or to prevent cold sores when exposed to triggering factors (e.g. Sun). In these special cases, medications may decrease by 1 day or 2 the time required for healing;

cures for cold sores that are offered over the counter. These products are usually offered in the form of liquid, ointment, gel or balm. They may contain hydrating and lip-protective agents as well as anesanting agents intended to reduce pain due to cold sores as well as to prevent chapping and excessive lip drying. These products can help relieve symptoms but does not stop the progression of the lesion or the replication of the virus.

docosanol, a viral entry inhibitor agent when applied at the earliest symptoms, exerts an action that helps prevent the spread of the virus to a healthy tissue. This will help limit the growth of wildfires. It reduces the healing time and the duration of the symptoms of the wild fire including pain, burning sensation, tingling and itching.

If possible, try to limit your exposure to the triggering factors described in the “causes” section. For example, if the Sun tends to cause the onset of cold sores, apply sunscreen with at least 30 protection factor on your lips and face 30 minutes before exposing yourself to the Sun. You should also avoid tanning beds. In addition, reduce your stress by eating well, getting enough rest and relaxation as well as exercising.

In people who often have severe cold sores or have a weakened immune system, the doctor may prescribe drug treatment on an ongoing basis in order to inhibit the virus.

To avoid being contaminated with herpes simplex virus, it is essential to avoid contact with it. Never touch the active lesions of other people.

When the cold sores are active, wash your hands frequently to avoid transmitting the virus to others. Try not to approach newborns or those with weakened immune systems, as these people are more susceptible to changing cold sores.

* All medicines have both a common denomination (a generic name) and a brand or brand name. The brand is the name that a manufacturer chooses for its product (e.g. Tylenol®). The generic name is the name of the medicine (e.g. acetaminophen). A drug can bear several brand names, but it has only one generic name. This article lists the medications by their generic name. For information on a given drug, consult our drug database. For more information on brand names, consult your doctor or pharmacist.


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