Cold Sore


The information provided below is for readers based in the United States of America. Readers outside of the United States of America should seek the information from local sources.

What is a cold sore?

Also known as herpes labialis, a cold sore is caused by the virus herpes simplex 1 (HSV-1), and less frequently by the herpes simplex 2 (HSV-2), and it appears in the mouth, mostly on the lips. During pregnancy, the HSV infection can be primary, meaning that you acquired the virus recently, or it can be a recurrent outbreak of an infection that you have had for a long time and which your immune system has been keeping under control.

How common are cold sores during pregnancy?

In the US, 54 percent of people ages 14-49 have been infected with HSV-1 or HSV-2 at some point, in most cases HSV-1. The risk of the virus producing sores is thought to be higher during pregnancy than in non-pregnant women, because of hormonal changes that affect the immune system. In most cases, cold sores are associated with HSV-1, whereas HSV-2 is associated with genital herpes sores, but there has been some flip-flopping reported in a small number of cases.

How is a cold sore diagnosed?

Often, your doctor can diagnose a cold sore simply by observing it. There may also be hints, such as swollen lymph nodes, or general symptoms of infection, such as fever or headache. Your doctor may sample the sore with a swab to obtain fluid that can be analyzed for the presence of HSV-1 and HSV-2.

Does a cold sore cause problems during pregnancy?

Usually, the HSV infection that causes cold sores is limited to the mouth, in which case the main problem is pain. You also may experience general symptoms of an infection, such as fever and headache. In rare cases of HSV-1, however, a serious infection of the brain, called herpetic encephalitis can develop in the late second to early third trimester.

Does a cold sore during pregnancy cause problems for the baby?

With cold sores resulting from a primary infection with HSV-1, or from a reactivation of HSV-1 that is limited to the mouth, you can expect a normal pregnancy and delivery with a good outcome for the baby. With genital sores, which tend to come from HSV-2 but also could result from HSV-1, there is a possibility of transferring the virus to the baby during delivery. There is also a small chance of infecting a newborn from sores that are limited to your mouth. Either situation could lead to neonatal herpes, a serious condition that can be fatal.

What to consider about taking medications when you are pregnant:

  • The risks to yourself and your baby if you do not treat the cold sore
  • The risks and benefits of each medication you use when you are pregnant
  • The risks and benefits of each medication you use when you are breastfeeding

What should I know about using medication to treat cold sores during pregnancy?

An anti-viral drug called acyclovir, and a similar drug called valacyclovir, are available to treat HSV-1 and HSV-2. Since these drugs also are used to treat viral infections in neonates, there is no concern that the drugs reaching the developing baby could do harm. On the contrary, they might help protect the baby from becoming infected. If you develop a fever, you can use acetaminophen or paracetamol, which are considered safe in pregnancy.

Who should NOT stop taking medication for cold sores during pregnancy?

If your doctors decide that you require an antiviral drug to take control of the infection, or to prevent infection of the baby, you are better off continuing with the treatment.

What should I know about choosing a medication for cold sores during pregnancy?

You may find Pregistrys expert reports about the individual medications to treat cold sores here. Additional information can also be found in the sources listed at the end of this report.

What should I know about taking a medication for my cold sores when I am breastfeeding?

Acyclovir is considered safe during breastfeeding. Furthermore, acetaminophen and paracetamol, which are given to treat the fever that can come with cold sores, are thought to be relatively safe in mothers who breastfeed.

What alternative therapies besides medications can I use to treat my cold sores during pregnancy?

There is no substitute for medication, but there are preventive measures that can be taken to avoid spreading the condition, for instance when you have a dental procedure. In some cases, dental treatment is better postponed until your sores are under control.

What can I do for myself and my baby when I have cold sores during pregnancy?

Make sure that your doctor and your dentist are in communication.

Resources for cold sores in pregnancy:

For more information about cold sores during and after pregnancy, contact (800-994-9662 [TDD: 888-220-5446]) or read the following articles:


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General information

It is very common for women to worry about having a miscarriage or giving birth to a child with a birth defect while they are pregnant. Many decisions that women make about their health during pregnancy are made with these concerns in mind.

For many women these concerns are very real. As many as 1 in 5 pregnancies end in a miscarriage, and 1 in 33 babies are born with a birth defect. These rates are considered the background population risk, which means they do not take into consideration anything about the health of the mom, the medications she is taking, or the family history of the mom or the baby’s dad. A number of different things can increase these risks, including taking certain medications during pregnancy.

It is known that most medications, including over-the-counter medications, taken during pregnancy do get passed on to the baby. Fortunately, most medicines are not harmful to the baby and can be safely taken during pregnancy. But there are some that are known to be harmful to a baby’s normal development and growth, especially when they are taken during certain times of the pregnancy. Because of this, it is important to talk with your doctor or midwife about any medications you are taking, ideally before you even try to get pregnant.

If a doctor other than the one caring for your pregnancy recommends that you start a new medicine while you are pregnant, it is important that you let them know you are pregnant.

If you do need to take a new medication while pregnant, it is important to discuss the possible risks the medicine may pose on your pregnancy with your doctor or midwife. They can help you understand the benefits and the risks of taking the medicine.

Ultimately, the decision to start, stop, or change medications during pregnancy is up to you to make, along with input from your doctor or midwife. If you do take medications during pregnancy, be sure to keep track of all the medications you are taking.

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