Patient information from BMJ

Cold sores

Last published:Aug 03, 2021

Cold sores are annoying and can be painful. They usually heal in a week to 10 days, although they can come back from time to time. If you are bothered by them there are treatments that can help.

What are cold sores?

Cold sores are blisters that appear on the lips and around the mouth. They are caused by a virus called herpes simplex. Cold sores are sometimes called herpes labialis or fever blisters.

There are two types of herpes simplex virus: 1 and 2. Type 1 mostly causes cold sores. Both types can cause sores on the genitals. This information is for people who get sores on their mouth.

You can catch herpes simplex from other people through their saliva. Most people are first infected as children.

Some children get quite ill when they are first infected. They might get ulcers inside their mouth and find swallowing painful.

They might also have fever, swollen glands, bad breath, a poor appetite, or little energy.

If your child has these symptoms, take them to the doctor. Treatment can help.

Once you are infected, the herpes simplex virus stays in the nerves in your face. It can cause further cold sores at any time.

Certain things seem to trigger new attacks, including:

• throat infections

• your periods (if you are a woman)

• sunlight, and

• certain medicines, including steroids.

It's possible to get a more serious illness from the herpes simplex virus, but this is rare. However, people who have a weak immune system have more chance of more serious problems.

If you have a weak immune system (for example, from HIV or from cancer treatment) and you get symptoms of herpes simplex infection, see your doctor.

What are the symptoms?

Cold sores start as red patches and become small blisters. When the blisters burst the skin becomes an open sore. Some people also get a fever. Your skin returns to normal in a week to 10 days.

Some people get a tingling or burning feeling on their lips about two days before their blisters appear.

Cold sores are usually at their most severe the first time you get them. If you get another outbreak of symptoms it will probably be milder than the first and your symptoms will probably go away more quickly (although the sore might take about the same amount of time to heal).

You are most likely to pass the virus to other people through your saliva when you have cold sores, or feel them coming on.

To reduce this risk, avoid kissing during these times and don't share food, drinks, and cutlery. Also, avoid giving oral sex when you have a cold sore.

What treatments work?

Cold sores usually clear up without any treatment in seven to 10 days. But there are some things you can try to help prevent and treat attacks.

Things you can do yourself

If sunlight triggers your cold sores, you might try using sunscreen on your lips and mouth to protect your skin from the sun. This might reduce the chance of new cold sores.

If your cold sore is painful you can take pain medicines, such as paracetamol or ibuprofen. You might also try rubbing a pain-relieving gel called lidocaine on the affected area.

Some people use antiviral creams when they feel a cold sore coming on. These are available over the counter at pharmacies. But they don't work as well as prescription antiviral tablets (see below).

Prescription medicines

Doctors sometimes prescribe antiviral medicines to treat bad cold sores, often during first outbreaks.

Your doctor might also suggest them if you get cold sores regularly or if you have a weak immune system. They seem to work better than antiviral creams.

But most people who don't have regular outbreaks don't need prescription antiviral medicines because cold sores usually go away on their own without causing serious problems.

Your doctor can prescribe antiviral medicines as tablets, or as a liquid for babies or young children.  They can help speed up healing and reduce pain. 

Taking antiviral drugs just before the cold sore appears (if you get early symptoms like tingling) or as soon as they appear can speed up recovery.

If you have frequent or severe cold sores your doctor might suggest that you take antiviral drugs every day. This can cut down on how often you get cold sores.

Antiviral drugs don't usually cause side effects in most people. Some people get headaches or feel sick, but these effects are usually mild and don't usually stop people taking their treatment.

What will happen to me?

Once you get a first cold sore you are likely to get them again. But for most people these usually clear up without treatment in about 7 to 10 days. If you are bothered by a cold sore, have a weak immune system, or get them frequently, see your doctor.