Cold Sores: Causes, Symptoms and Treatments


MNT Knowledge Center

Cold sores, also known as fever blisters, are small sores, or blister-like lesions on the face or inside the mouth. They usually cause pain, a burning sensation, or itching before they burst and crust over. Most commonly, cold sores appear on the lips, chin, cheeks, inside the nostrils, and less frequently on the gums or the palate (roof of the mouth).

Cold sores are caused by the herpes simplex viruses; the most common cause of sores around the mouth is herpes simplex type 1, or HSV-1. Much less commonly, cold sores may be caused by HSV-2 (herpes simplex type 2), which may result from having oral sex with a person who has genital herpes.

Cold sores are different from canker sores. However, people sometimes mistakenly associate one with the other. A canker sore is a small ulcer crater in the lining of the mouth – it is frequently painful. Canker sores are also known as aphthous ulcers. Canker sores occur in the soft tissue of the mouth, where cold sores do not appear.

Cold sores are quite common. There is no cure or prevention for infected people, but steps can be taken to reduce their frequency and duration.

The herpes simplex virus

The cold sore virus or herpes simplex virus is very contagious – it is easily transmissible from human-to-human as a result of close contact. When it enters a human, for most of the time it remains inactive (dormant). Occasionally, however, certain triggers activate the virus, resulting in a cold sore outbreak. Triggers vary, according to the individual. While one person may have just one outbreak and no recurrence, others may have two or three each year. Some people may carry the virus and never have an outbreak because it remains dormant all the time.

Contents of this article:

  1. Signs and symptoms of cold sores
  2. What causes cold sores?
  3. Diagnosis of cold sores
  4. Treatment options for cold sores
  5. Possible complications of cold sores
  6. Prevention and stemming the spread

Fast facts on cold sores

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

  • Cold sores are tiny blisters that develop on the lips or around the mouth.
  • Cold sores are caused by the herpes simplex virus strain HSV-1.
  • On rare occasions cold sores may be caused by strain HSV-2 – a result of having oral sex with someone who has genital herpes.
  • Cold sores usually clear within 7-10 days without treatment.
  • The herpes simplex virus is highly contagious and can be easily passed from person to person by close direct contact.
  • After someone has contracted the “cold sore virus”, it remains inactive for most of the time.
  • The virus can be activated by triggers such as fatigue, injury to the affected area, and in women – their period.
  • Some people have cold sores recur around 2-3 times per year.
  • Statistical studies suggest that about 80-90% of people in the US have been exposed to HSV-1 and about 30% have been exposed to HSV-2.
  • It is not possible to completely prevent becoming infected with the herpes simplex virus or to prevent outbreaks of cold sores.
  • If you have unhealed cold sores, it is particularly important to avoid close contact with people with weakened immune systems.

Signs and symptoms of cold sores

A symptom is something the patient feels and reports, while a sign is something other people, including a doctor or a nurse may detect. For example, pain may be a symptom while a rash may be a sign.

Many people infected with the herpes simplex virus have no symptoms and will never know they are infected, until an outbreak of cold sores occurs (if ever one does). If there are symptoms with a primary infection, they may be severe.

Signs and symptoms of the primary infection

(Primary infection – the original outbreak of an illness against which the body has had no opportunity to build antibodies.)

In the majority of cases there are no detectable signs or symptoms. When they do occur, usually in very young children, they may be severe, and can include:

  • Mouth or tongue lesions
  • Blisters in the mouth
  • Mouth ulcers
  • Mouth or tongue pain
  • Lip swelling
  • Possible swallowing difficulties
  • Sore throat
  • Swollen glands
  • Elevated body temperature
  • Dehydration (body does not have enough water)
  • Nausea
  • Headaches.

A cold sore on a young person's face
Cold sores commonly develop on the lips or around the mouth

Herpes simplex gingivostomatitis may last from one to two weeks. The sores may take as long as three weeks to heal up. After the primary infection, gingivostomatitis does not recur; just normal cold sore outbreaks may recur. Although adults can get gingivostomatitis, most patients are young children.

Adults with primary infection usually have pharyngotonsillitis – the tonsils will swell, the individual will have a sore throat and glandular fever-like symptoms. The glands may or may not swell. A significant number of patients will have foul-smelling breath (halitosis) and painful sores around the mouth. These sores sometimes develop into ulcers with grayish-yellowish centers.

Individuals who were infected when they were children may have occasional bouts of cold sores later in life. However, after the primary infection, signs and symptoms are generally limited to just those of cold sores.

Cold sore signs and symptoms (symptoms of recurrent infection)

A recurrent infection is nearly always less severe and shorter-lasting than the primary infection. There will be an outbreak of cold sores, with the possibility swollen glands (less common).

Patients say a tingling, itching or burning sensation around the mouth often indicates the onset of a cold sore outbreak. This is followed by fluid-filled sores, typically located on the edges of the lower lip.

People with regular recurrences say the cold sores often appear in the same place. As the cold sore grows in size, so does the pain and irritation. They will form, break and ooze (weep). A yellow crust forms and sloughs off to uncover pink skin that heals without scarring.

In the majority of cases the cold sore is gone within a week or two.

What causes cold sores?

Most cases of cold sores are a consequence of infection with HSV-1 (herpes simplex virus type 1). Infection with HSV-2, usually resulting from oral sex with a person who has genital herpes, is a much less common cause of cold sore outbreaks.

HSV-1 is typically passed on in early childhood when a child is kissed by a person with a cold sore. Shared eating utensils, bathroom items, such as towels or razors, may spread the infection. The virus makes its way to the nerves and lies there dormant until some trigger activates it later on.

The following triggers are known to potentially activate the virus:

  • Mental stress
  • Deep sadness or upset
  • An injury to the affected area
  • Menstruation
  • Intense sunlight.

On the next page we look at how to diagnose a cold sore and the possible treatment options for cold sores.


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Diagnosis of cold sores

Anyone who has had a cold sore outbreak will easily recognize a recurrence. People who think 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.

A GP will usually be able to make a diagnosis just by looking at the cold sore(s). Sometimes a blood test may be ordered. The doctor may also take a sample of the fluid scraped from the cold sore – the aim is to detect the presence of the cold sore virus. Such tests are generally only done on patients with weak immune systems, such as those undergoing chemotherapy, or people with HIV/AIDS.

Treatment options for cold sores

Most cases of cold sore outbreaks will clear up within one to two weeks without any treatment. Some ointments and antiviral medications may slightly shorten the duration of the outbreak and alleviate discomfort and pain.

A cold sore being treated
Some over-the-counter creams
can help alleviate the irritation.

  • Antivirals – OTC (over-the-counter, no prescription required) cold sore antiviral creams can shorten the duration of a recurrent infection if used properly. Most creams contain either acyclovir or penciclovir (Zovirax, Soothelip). They are only effective if applied as soon as symptoms appear – right at the beginning, when the tingling sensation occurs and the individual knows a cold sore is about to come. The cream needs to be applied up to five times daily for 4 to 5 days for best effect. These creams cannot prevent future occurrences – they do not eliminate the virus.
  • Patients with weakened immune systems – there is a risk of complications for patients undergoing chemotherapy, or those with HIV; the infection may spread to other parts of the body, including the eye, and there is also a risk of swelling of the brain (encephalitis). Such patients may be prescribed antiviral tablets or be referred to a specialist. Treatment depends on the severity of symptoms, and the type of illness the patient has.
  • Other treatments for cold sores – some creams which do not contain antivirals and can be bought without a prescription may help alleviate some of the irritation. They do not speed up the healing process, but may help if the cold sores are very dry, itchy or painful. Examples include Bonjela, Blistex, or Cymex. Dab them straight onto the sores; don’t rub. Make sure you wash your hands thoroughly with warm water and soap after applying the cream. Make sure nobody else uses the cream.
  • Painkillers – ibuprofen or Tylenol (paracetamol) may help alleviate pain. If the patient is a young child ask the pharmacist for those medications in liquid form. If the patient is asthmatic, or has/had stomach ulcers he/she should not take ibuprofen. People under 16 years of age should not take aspirin.

Pregnant women who have cold sores should discuss their treatment options with their doctor.

Herpes simplex gingivostomatitis treatment – your general practitioner (GP, primary care physician) should be consulted for treatment options.

  • Benzydamine – either as an oral rinse or spray helps alleviate pain in the mouth or throat.
  • Antiseptic mouthwash – this may help prevent secondary infections and control plaque build-up. Some patients find brushing their teeth too painful and cannot do it properly.
  • Painkillers – ibuprofen or Tylenol (paracetamol) will help alleviate pain. See the above warnings for ibuprofen and aspirin.
  • Labial adhesions – sometimes the lips may stick together in places. A lip barrier cream, such as Vaseline will help prevent this.
  • Dehydration – patients with gingivostomatitis, especially young children, are at risk of becoming dehydrated because swallowing may be uncomfortable. It is important to keep drinking lots of fluids. The following signs and symptoms may indicate possible dehydration:

    • Fatigue
    • Irritability
    • Headache
    • Light-headedness
    • Producing very little urine

    If dehydration becomes serious the patient may need to have fluids administered intravenously (into a vein) in hospital.

    If the infection is severe, or gingivostomatitis symptoms continue for over two weeks, you should tell your doctor.

Possible complications of cold sores

Complications caused by cold sore virus are very rare, and tend to occur with patients who have weakened immune systems – even then, complications are not common. Possible complications include:

  • Dehydration – if there is pain in the mouth and throat the patient may be reluctant to drink. This is especially the case with herpes simplex gingivostomatitis.
  • Herpetic whitlow – if the cold sore virus spreads to other parts of the body, for example the hands, the patient may have blisters on their fingers. Most commonly the virus spreads by entering through a cut or graze in the skin. Antiviral medications are generally effective in treating this type of complication.
  • Herpetic keratoconjunctivitis – this is a secondary infection in which the eyes are affected. The eye area may become swollen and irritated (inflamed), and sores may develop on the eyelids. If left untreated the cornea may become infected, resulting in possible blindness. This type of complication is usually effectively treated with antiviral medication.
  • Encephalitis – the brain becomes swollen and there is a serious risk of brain damage. Encephalitis can be life-threatening. Encephalitis can occur if the cold sore virus spreads to the brain. Fortunately, this type of complication is extremely rare. Antiviral medications are injected straight into the patient’s bloodstream. Treatment is usually effective.

Prevention and stemming the spread

When sores are present:

  • Avoid kissing other people
  • Avoid skin contact with other people
  • Avoid sharing things, such as towels, lipstick, lip balm, cutlery, etc.
  • Follow good hand hygiene.
  • Avoid touching the sores. If you do, wash your hands with soap and warm water immediately.
  • Avoid touching other parts of your body, especially susceptible areas, such as the genitals and eyes.

There are certain triggers which can bring on an outbreak. These include mental stress, catching colds and flu, sleep deprivation, or too much sun. If you follow a healthy diet, which includes plenty of fruits and vegetables, you chances of catching a cold or flu may be significantly reduced. Sunblock can help reduce your skin’s exposure to sunlight.