What are cold sores?

Cold sores are small blisters around the mouth. They are also called fever blisters. They are caused by the herpes simplex virus. The most common strain of the virus causing cold sores is herpes simplex virus 1. It can be spread by kissing or sharing eating utensils or even sharing towels.

Herpes simplex is not curable. But may stay inactive for a long time.

What causes cold sores?

Cold sores are caused by the herpes simplex virus. Once this virus is in you, it can cause outbreaks of cold sores. Cold sore outbreaks are often triggered by exposure to hot sun, cold wind, a cold or other illness, a weak immune system, changing hormone levels, or even stress.

What are the symptoms of cold sores?

Some people don’t have any symptoms with the first attack. Others have flu-like symptoms and sores (ulcers) in and around the mouth. Symptoms may occur a bit differently in each person. These are the most common symptoms:

• Tingling of the lips, commonly felt before cold sores appear 

• Small blisters on the lips and mouth that enlarge, burst, then crust over

• Itching, dryness, and irritation of the lips and mouth

• Soreness of the lips and mouth

How are cold sores diagnosed?

Your healthcare provider can often diagnose cold sores by looking at the sores. If the diagnosis is unclear, your provider may swab the sore and send it to the lab for examination.

How are cold sores treated?

Cold sores can’t be cured. But if symptoms are severe, treatment may help ease some symptoms. Treatment may include:

• Antiviral ointments such as acyclovir and penciclovir to put on the sores. These work for some people but are often not very helpful.

• Antiviral oral medicines such as acyclovir, famciclovir, and valacyclovir may decrease the time the sores are present or their severity.

• Over-the-counter pain relief medicines to put on the sores (topical) may help with symptoms. Anti-inflammatory medicines may also help.

Cold sores take about 1 to 3 weeks to heal. The first time they appear, they can take up to 3 weeks to heal. But when cold sores return, they usually are less severe and take a week to heal if no medicines are used. Antiviral medicines may help, but they work best if started with early symptoms before a blister appears. Antivirals are usually not advised for otherwise healthy people. Always talk your healthcare provider or dentist if the sore doesn't heal or becomes worse as time passes.

Can cold sores be prevented?

If you have never had a cold sore, don't have skin-to-skin contact with someone who has an active cold sore. If you have had a cold sore, you may prevent or reduce the number of times they come back by finding out what triggers your outbreaks. Then stay away from that trigger. For instance, if sun exposure is a trigger, use sunscreen when in the sun. If you have outbreaks often, talk with your healthcare provider. Starting treatment as soon as you know you are getting a cold sore can help it heal faster.

The long-term use of oral antiviral medicines may prevent cold sores, but the benefit is very small. This approach is usually used only for people who get frequent and painful cold sores. Antiviral medicines put on the sores don't help prevent them.

Key points about cold sores

• Cold sores are small blisters around the mouth caused by the herpes simplex virus.

• Cold sores can be spread by kissing or sharing eating utensils or even sharing towels.

• Tingling often happens before the blisters appear.

• Cold sores cause small blisters on the lips and mouth that enlarge, burst, then crust over.

• Early treatment can promote healing and reduce the time it takes a cold sore to heal.

• Using antiviral medicine on the sores does not prevent them or help them heal faster.

Next steps

Tips to help you get the most from a visit to your healthcare provider: 

• Know the reason for your visit and what you want to happen.

• Before your visit, write down questions you want answered.

• Bring someone with you to help you ask questions and remember what your provider tells you.

• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.

• Know why a new medicine or treatment is prescribed and how it will help you. Also know what the side effects are.

• Ask if your condition can be treated in other ways.

• Know why a test or procedure is recommended and what the results could mean.

• Know what to expect if you do not take the medicine or have the test or procedure.

• If you have a follow-up appointment, write down the date, time, and purpose for that visit.

• Know how you can contact your provider if you have questions.