What Are the Symptoms of Cold Sores?

February 24, 2026

The symptoms of the herpes simplex virus vary, depending on the person and the stage at which they're infected. For example, different symptoms will be seen in children compared to those an adult would experience, while the types found in the first infection will differ from those seen in recurrent cold sore outbreaks.

The first infection in children

Because a primary (first-time) infection is often similar to a throat infection, it may sometimes be diagnosed as such. Usually seen in those under the age of five, the primary symptoms presented in children can include all or some of the following:

Herpes simplex gingivostomatitis – described by the NHS in England as "swollen and irritated gums with small, painful sores in and around the mouth
Sore throat
Swollen throat glands
An increase in the production of saliva
A temperature
Dehydration
Feeling sick
Headaches

First-time exposure to the HSV virus is usually harmless and no cause for alarm from parents. However, it's always best for parents to take their child to the doctor.

Symptoms are at their worst during the primary infection. When the virus reactivates, cold sores are likely to be the only symptom.

It's important to remember that in the vast majority of cases if a child catches the HSV virus there is usually no need to worry. However, adults should practice a great deal of caution around babies, whose immune systems are yet properly developed. Parents and close family members with active fever blister outbreaks should never kiss a baby. There are unfortunately a number of cases where parents have kissed their child, even when they are not displaying visible cold sores and have caused their child to suffer from neonatal herpes, which can potentially be fatal if the virus spreads to the baby's organs.

If your child is experiencing any of the above symptoms, we recommend seeing a medical professional, as they can also be signs of other medical issues.

Primary infection in adults

It is rare for adults to experience a primary infection. However, when they do, the symptoms are similar to those suffered by children.

Adults may complain of a sore throat, fever, blisters and, potentially, swollen glands. They might also notice bad breath. The blisters around their mouths are likely to develop and will eventually turn into ulcers, typically with grey or yellow centers to them.

Recurring cold sore symptoms

Although some people might suffer from swollen glands during a recurring outbreak, usually the only symptoms experienced following initial exposure are the fever blisters themselves.

The beginnings of the cold sore

The virus lies dormant in the ganglion and is controlled by the immune system. Factors which weaken the immune system, including overexposure to UV light, febrile illness and stress, can trigger the reactivation of the virus.

Sufferers of recurrent cold sores may already be familiar with the warning signs that an outbreak is coming. The telltale signs that a fever blister outbreak is on its way include feeling a tingling, itching, burning, or numbing sensation somewhere around the mouth area. These sensations are caused by the cells dying as the virus replicates itself.

Visible symptoms present themselves

After about a day, the person will notice small, fluid-filled blisters appearing. This is often the most painful stage and will typically last two days before the small blisters turn into larger ulcers.

These usually form somewhere on the outer edges of the lips and tend to reappear in the same place during every outbreak. The usual area affected will depend upon which sensory nerves the virus uses to travel back towards the skin cells, where it reactivates after dormancy.

The repairing time

Normally these ulcers will weep before scabbing over a few days later. They will completely heal without a scar shortly after this period. It's important to remember that cold sores remain very contagious from the first tingle to the time they've completely healed over, so you should take precautions, such as avoiding kissing and not sharing utensils, until the blister has completely healed.

Although cold sores will only last from eight to twelve days without treatment, the amount of discomfort, and potential embarrassment, suffered by an individual during this time is well worth trying to reduce or avoid altogether.

While most sores will heal in a relatively short time, sometimes the sore takes a lot longer to heal. If a fever blister hasn't healed after 10 days, appears to be more severe than your usual outbreaks, or if you're unsure about whether the lesion is a cold sore, then it's a good idea to make an appointment with your GP.