Understanding Cold Sores

Cold sores are small blisters or sores on the lip or sometimes inside the mouth. Many people get them from time to time. Cold sores usually are not serious, and they usually heal in a week or two. They are caused by 2 related viruses, herpes simplex type 1 and 2. These viruses spread very easily. Many people have one or both of these viruses in their body. More than 4 in every 5 people are infected with herpes simplex type 1. Once you have the virus that causes cold sores, it stays in your body for the rest of your life. But it can be inactive for long periods.

What causes a cold sore?

Cold sores are usually caused by herpes simplex virus type 1. Less often, they are caused by herpes simplex virus type 2. Herpes simplex virus type 2 is the more common cause of genital sores. The herpes viruses can enter the body through a break in the skin such as a scrape. Or they may enter through mucous membranes such as the lips or mouth. Some ways to get the viruses include:

  • Kissing someone who has a cold sore

  • Sharing a drinking glass, eating utensils, or lip balm with someone who has a cold sore

  • Having oral sex with someone who has a cold sore

A newborn baby can also get the infection at birth.

If you have a herpes virus, you can to pass it along even when you don’t have a sore.

Cold sores flare up occasionally. Things that can cause an outbreak include:

  • Sun exposure

  • Fever

  • Stress or exhaustion

  • Menstruation

  • Skin irritation

  • Another unrelated Illness such as pneumonia, urinary infection, or cancer

What are the symptoms of a cold sore?

Symptoms can include:

  • A blister-like sore or cluster of sores. These often occur at the edge of the lips but may appear inside the mouth.

  • Skin redness around the sores.

  • Pain or itching in the area of the outbreak. Often the pain or itching develops 12 to 24 hours before the sore become visible.

  • Flu-like symptoms, including swollen glands, headache, body ache, or fever. These typically occur only at the time of the first infection.

Cold sores may also occur on fingers. They may rarely infect the eyes, a serious possible complication.

Some people have symptoms a day or two before an outbreak. They may feel tenderness, burning, itching, or tingling before a cold sore appears. Cold sores tend to come back in the same area that they first appeared.

How are cold sores treated?

Treatment for cold sores focuses on relieving and shortening symptoms. For people with frequent outbreaks, treatment works to decrease how often future episodes.  Treatments may include:

  • Prescription or over-the-counter pain medicines. These can help with discomfort, especially if sores are inside the mouth.

  • Antiviral medicines. These may be pills that are taken by mouth or a cream to apply to sores. They may help shorten an outbreak and reduce the severity of symptoms.  They may be used to help prevent future outbreaks if you have disabling recurrent infections.

  • Self-care such as extra rest and drinking more fluids. These may help relieve the flu-like symptoms of a first outbreak.

How are cold sores diagnosed?

Your healthcare provider makes the diagnosis mainly by looking at the sores and doing a clinical exam.  This may be confirmed by swab tests or blood tests.

How can I prevent cold sores?

You can help reduce the spread of the herpes viruses that cause cold sores. This can help both you and others avoid getting cold sores. Follow these tips:

  • Do not kiss others if you have a cold sore. Also avoid kissing someone with a cold sore.

  • Do not share eating utensils, lip balm, razors, or towels with someone who has a cold sore.

  • Wash your hands after touching the area of a cold sore. The herpes virus can be carried from your face to your hands when you touch the area of a cold sore. When this happens, wash your hands thoroughly, for at least 20 seconds. When you can’t wash with soap and water, use an alcohol-based hand sanitizer.

  • Disinfect things you touch often, such as phones and keyboards.  

  • If you feel a cold sore coming on, do the same things you would do when a cold sore is present to avoid spreading the virus.

  • Use condoms to help prevent passing on the viruses through sex.

What are the possible complications of a cold sore?

Cold sores usually go away by themselves within 2 weeks. For most people cold sores are not serious. The viruses that cause cold sores can cause more serious illness, though. People who have a weak immune system may get more serious infections from herpes viruses. These include people being treated for cancer or who have HIV disease. Babies may also become very ill from a herpes infection. 


When should I call my healthcare provider?

Call your healthcare provider right away if you have any of these:

  • Fever of 100.4°F (38°C) or higher, or as directed

  • Pain that gets worse

  • You cannot eat or drink because of painful sores

  • Symptoms don’t get better within 5 to 7 days

  • Blisters spread beyond the mouth or lip to areas on the chest, arms, face, or legs