Is a Cold Sore Dangerous for a Growing Fetus?

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Cold Sore Growing Fetus

You may already know that it’s important to avoid certain infections during pregnancy. One of these infections is the herpes simplex virus (HSV), or herpes. There are two types of herpes: HSV-1 is usually associated with oral (in and around the mouth) infections, and HSV-2 is more commonly associated with sexually-transmitted genital disease. However, HSV-1 can also be spread through oral-genital contact and cause genital infections.

What Do I Need to Know About HSV-1?

  • An active infection can cause painful blisters or ulcers at the site(s) of infection.
  • An active infection on the lip(s) is often called a “cold sore” or “fever blister.”
  • The blisters tend to take a few weeks to go away, and they can come back at any time.
  • Many people with herpes do not have symptoms or have mild symptoms and often do not know they are infected.
  • The virus is highly contagious.
  • It is more contagious when sores are present, but it can also be spread without sores.
  • There is no cure for the virus – once you have it, it stays in your body for life.1,2

Is My Baby Safe?

Congenital herpes occurs when the fetus gets the virus during pregnancy. This is rare (only 5% of herpes infections in the neonate) and is usually caused by HSV-2. Neonatal herpes occurs when a baby is exposed to the virus in the genital tract during delivery. It’s caused by HSV-2 in 85-90% of cases, HSV-1 in the rest.3 This is also rare, but it can cause severe disease or death when it does. A cesarean section may be performed for a woman with genital infection.4

Unfortunately, there is not much research on oral HSV-1 infection during pregnancy. There are some documented cases of pregnant women passing along the infection to their unborn babies, but the exact risk isn’t clear.5 Pregnant women with cold sores are urged to discuss with their obstetricians, as documentation, observation, and/or treatment with anti-viral medication may be needed.

Mothers with active infections should also exercise caution after giving birth. According to the American College of Obstetricians and Gynecologists, “The herpes virus cannot be passed to a baby through breast milk. However, the baby could get infected by touching a sore on your body. Make sure any sores that the baby could come into contact with are covered when you hold your baby or while breastfeeding. Wash your hands with soap and water before and after feeding your baby. If you have sores on your breast, you should not breastfeed your baby from that breast.”4

How to Prevent Spreading

Here are a few tips on how to help prevent spreading the infection:

  • Don’t share anything that touches your mouth – this means forks, spoons, lip balm, etc.
  • Wash your hands often, especially after eating or touching your mouth
  • Avoid contacting the area during an active infection


  1. World Health Organization. Herpes Simplex Virus.
  2. Mayo Clinic. Cold Sore.
  3. Straface G, et al. Herpes Simplex Virus Infection in Pregnancy.
  4. American College of Obstetricians and Gynecologists. Genital H
  5. Healy SA, et al. Primary Maternal Herpes Simplex Virus-1 Gingivostomatitis During Pregnancy and Neonatal Herpes.
Mandy Armitage
Dr. Mandy Armitage is a board-certified physician and writer. She is passionate about education, for patients and clinicians alike. In her free time, she enjoys spending time with her family, reading, traveling, and attending live music events.

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