Understanding Cold Sores

Cold sores (fever blisters) are small sores or blisters on the lip. Sometimes they are inside the mouth. Many people get them from time to time. Cold sores often are not serious. They often heal in a few days, sometimes longer. They are caused by 2 related viruses, herpes simplex type 1 (HSV-1) and herpes simplex type 2 (HSV-2). These viruses spread very easily. Most people have HSV-1 in their body; many also have HSV-2. More than 4 in every 5 people are infected with HSV-1. This is the most common cause of cold sores. 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 often caused by HSV-1. In some cases, they are caused by HSV-2. HSV-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 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 pass it along even when you don’t have a sore.

Cold sores flare up from time to time. 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 starts 12 to 24 hours before the sore is 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 2 before an outbreak. They may feel soreness, burning, itching, or tingling before a cold sore appears. Cold sores often come back in the same area that they first appeared.

How are cold sores treated?

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

  • Prescription or over-the-counter pain medicines. These can help with mild pain, 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 infections that keep coming back.

  • Self-care such as extra rest and drinking more fluids. These may help ease 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 prevent both you and others from getting cold sores. Follow these tips:

  • Don't kiss others if you have a cold sore. Also don't kiss someone with a cold sore.

  • Don't 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 prevent 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 often go away by themselves within a few days. In some cases, it may take 1 to 2 weeks or longer. For most people, cold sores are not serious. But the viruses that cause cold sores can cause more serious illness. People who have a weak immune system may get more serious infections from herpes viruses. These include people being treated for cancer or people who have HIV. 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 by your provider

  • Pain that gets worse

  • You can't eat or drink because of painful sores

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

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