Primary Cold Sore Infection

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A first (primary) infection with the cold sore virus is often different to the repeated (recurring) cold sores which many people have. Frequently there are no symptoms. Sometimes an unpleasant mouth infection develops. Treatment aims to ease symptoms while the infection gradually settles over 1-3 weeks.

Cold sores are caused by the herpes simplex virus (HSV). The first time you are infected with this virus is called the primary infection. The mouth is the area commonly affected. This is because normal skin is resistant to the virus but the moist inner skin of the mouth is not. The first (primary) infection is usually in childhood. It is often caught by kisses from a family member who has a cold sore. Primary cold sore infection can be worse than recurrent mouth ulcers but luckily some people don't experience any symptoms at all.

This leaflet will deal with primary cold sore infection. See separate leaflet called Cold Sores for more details on recurrent cold sores.

Symptoms of the first (primary) infection are often different to recurring cold sores.

  • You may have no symptoms, or only trivial ones. For example, you may not realise that a tiny spot on the tongue is a first cold sore. However, you may then develop typical cold sores from time to time in the future.
  • You may have a more severe infection in and around the mouth.
    • Small blisters or ulcers may develop on the mouth, tongue, gums, lips, or throat. This is called gingivostomatitis. There may be only a few blisters but sometimes there are many.
    • The blisters and ulcers are painful. Swallowing or eating may become quite painful. The pain may cause you to pool (collect) saliva in the mouth and children may drool (dribble).
    • The glands in your neck may swell and become tender.
    • You may develop a high temperature (fever) and general aches and pains.
    • The infection gradually subsides and goes within 1-3 weeks.
  • Painkillers such as paracetamol or ibuprofen can ease the pain.
  • Benzydamine mouthwash or spray may be useful in relieving the pain from a sore ulcerated mouth.
  • Choline salicylate gel (Bonjela® dental gel) can be used in the mouth to reduce pain. Bonjela® should not be used in children under the age of 16, due to a potential risk of Reye's syndrome if it is overused. This is the same reason why aspirin cannot be used in children too. Note: Bonjela teething gel® no longer contains choline salicylate and has been reformulated with lidocaine, a local anaesthetic (to cause temporary numbing). This means that Bonjela teething gel® can be used in children.
  • Have plenty to drink. It may be painful to drink but it is important to drink to prevent lack of fluid in the body (dehydration).
  • If it is too painful to clean your teeth, chlorhexidine mouthwash (brand name Corsodyl® or Chlorohex®) can be used in place of brushing. It may help adults or children old enough to use it to keep the mouth and teeth clean, to prevent plaque build-up and secondary infection with germs (bacteria).
  • Sloppy foods such as yoghurts and soups are easier to eat when your mouth is painful. Cold or cool foods may be less painful than hot foods.
  • An antiviral medicine (such as aciclovir) is sometimes prescribed if the symptoms are severe. It is taken by mouth, rather than the topical creams used to rub on cold sores. It does not clear the virus but prevents the virus from multiplying. It may not have much effect once the blisters and ulcers are well developed. However, if taken early in the infection, it may reduce the duration of the pain and speed recovery a little.
  • Lip barrier preparations such as Vaseline® or Lypsyl® may make the lips feel more comfortable and may stop them from sticking or scabbing together.
  • General measures include trying to minimise the chances of passing the cold sore virus on to others. Careful hand washing with soap and water is important after touching the mouth and cold sores. You should avoid touching cold sores or ulcers in the mouth associated with first (primary) infection, except when applying medication. You should not have oral sex when you have either a primary cold sore infection or an individual cold sore. Finally, it is important not to share items that come into contact with infected areas - this would include lipsticks and lip balms.


Young children may be distressed with the pain and refuse to take medicine or drinks. Tips to help include:

  • Try using a syringe (which you can buy at pharmacies) to squirt medicine into the side of the mouth slowly. Do not squirt into the back of the mouth, as this may cause choking.
  • Keep offering cool drinks. You can also use a syringe to give some drinks. Again, slowly squirt into the side of the mouth, not towards the back of the mouth.
  • Sucking ice pops or ice cubes may help to ease the pain and are also a way of giving fluids.

Occasionally, a child stops drinking because of the pain in their mouth. They are then in danger of becoming dehydrated. If your child has stopped passing urine, or if their urine is dark in colour and strong-smelling, they are likely to be dehydrated. See a doctor if you are concerned that your child is not drinking enough and is becoming dehydrated. Some children who are at risk of dehydration are admitted to hospital for a short while until the infection settles and they are drinking normally again. In hospital they can have their fluid intake monitored and they can be given an intravenous drip if needed.

If your child is generally well with a primary herpes virus infection, they do not need to be kept off school or nursery.

You should seek medical advice at any time if you are worried about yourself or your child. This is particularly important if you have a weakened immune system (immunocompromised). Immunocompromised people include those with conditions such as AIDS, or those receiving chemotherapy or other medicines which lower the body's resistance to infections. Pregnant women and mothers with a young baby who is affected, should also seek prompt medical attention. Anyone with a first (primary) cold sore infection where the symptoms are not settling after five days, should see their GP.

After a first (primary) infection has cleared, the virus remains dormant (inactive) in a nerve sheath. For most of the time it causes no problems. In some people the virus 'activates' from time to time to cause cold sores around the mouth and nose. Repeated (recurrent) cold sores may be unpleasant but do not cause severe mouth infections like some primary infections. About 1 in 5 people in the UK have recurrent cold sores.

Further help & information

Original Author:
Dr Tim Kenny
Current Version:
Peer Reviewer:
Prof Cathy Jackson
Document ID:
4412 (v41)
Last Checked:
Next Review:
The Information Standard - certified member
Now read about Oral Herpes Simplex

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