Herpes labialis is caused by infection with the herpes simplex virus, which leads to the development of cold sores in or around the mouth. People do not usually experience any symptoms immediately after infection and the cold sore outbreak tends to occur some time later. However, if the primary infection does cause symptoms, they tend to be severe.

Symptoms of infection

In children

Children aged under five years are the most likely age group to develop symptoms of primary infection. Symptoms include swollen and aggravated gums and painful sores that develop in and around the mouth. This is referred to as herpes simplex gingivostomatitis.

In addition, the glands or lymph nodes in the neck may swell up and the child may have a sore throat. Saliva production may increase and temperature may reach 38ºC (100.4ºF) or above. The child may also experience nausea, vomiting and abdominal upset. Dehydration and headaches are other common features of primary infection. Herpes simplex gingivostomatitis is common in young children but it can also affect adults. The sores may last for around a week or two and may take up to three weeks to heal completely. Once the primary infection is over, these sores do not usually recur.

In adults

Symptoms of primary herpes simplex virus infection are rare among adults, but if they do occur, they are similar to those described for children. Adults will usually experience a sore throat that may or may not be accompanied by swollen glands; halitosis or bad breath may develop and painful sores may form in and around the mouth. The sores can eventually form ulcers, which have a yellow or grey coloured centre.

If a person is infected with the herpes virus simplex virus at a very early age, symptoms may be triggered intermittently throughout life. However, when symptoms recur, they are usually confined to just the cold sores. Outbreaks usually begin with an itching, tingling or burning sensation around the mouth, followed by the development of small blisters in the corners of the lower lip. The lesions usually clear up within 7 to 10 days.