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What Causes Cold Sores in a Baby's Mouth?

When a fluid-filled blister appears in or around your baby's mouth, she has a cold sore, which is sometimes called a fever blister. This means your child has contracted herpes simplex virus. Type 1 usually causes cold sores, though Type 2 -- usually related to genital herpes -- can as well. This virus may cause cold sores just once and then lie dormant for the rest of her life, or your baby may suffer from outbreaks for the rest of her life.

  1. A Kiss

    • Your baby may have contracted the virus that causes cold sores from a kiss on her mouth. People who carry the herpes simplex virus pass the virus along through physical contact with the sore. So if a friend or family member experienced a cold sore outbreak and kissed your baby on the lips, that person could have given her the virus. The virus may even be active in a person who isn't experiencing a visible breakout. If the virus is dormant or inactive, a person can't pass it onto another person.

    Vaginal Canal

    • A baby may also contract the virus for cold sores during birth. If the mother has genital herpes in her vaginal canal during childbirth, she can pass the virus onto her child. Type 2 can cause sores in the genital area or the mouth. According to the American Social Heath Association, mothers are more likely to infect their child with the virus if they contract herpes late in their pregnancy because the mother hasn't built antibodies against the virus yet. Mothers need these antibodies to protect their unborn children from the virus. However, mothers that contracted genital herpes before getting pregnant already have the antibodies needed to protect the baby, so they are less likely to pass the virus onto their child.

    Utensils

    • Your baby may be experiencing cold sores in her mouth because she shared a utensil, such as a spoon or fork, or a cup with a person actively carrying the herpes simplex virus. Infection occurs much like with a kiss. Even if a cold sore hadn't broken out on the adult's mouth area, he still could have given the baby the virus through his infected saliva.

    Toys

    • Your baby can get infected with the cold sore virus by sharing toys with another child who carries the virus. Babies and young children often put toys in their mouths. If the baby or child has a cold sore outbreak or the virus is active in their saliva, they can pass on the virus by putting the toy in their mouth, giving the toy to another child for him to put in his mouth.

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