OverviewMothers likely expect to experience some side effects related to breastfeeding themselves, from sore nipples to plugged ducts. However, babies can also face side effects as well, including blisters on their lips caused by breastfeeding. This blister is more unsightly than it is serious, so breastfeeding mothers should not cut back feedings or turn to the bottle simply because their baby has a lip blister. Understanding lip blisters can eliminate a mother's worry.CausesLip blisters are caused by vigorous sucking associated with breastfeeding. Some babies might even be born with these blisters if they sucked their thumb in the womb, according to Denise Porretto's article in "Parents" magazine. The repetitive movement of sucking, which newborns can do for hours a day, can cause these blisters or calluses on the baby's top lips.TimingLip blisters are more likely to appear in the first few months of a baby's life, according to the Ruch Clinic. During this stage, babies are nursing every two to three hours, and the frequency of the friction related to sucking can cause these blisters to appear. The blisters might go away after each feeding or last for weeks or months. After a few months, however, the blisters should go away for good as the baby adjusts to breastfeeding.TreatmentLip blisters do not require any treatment because they do not cause any discomfort to the baby. Mothers should not let these harmless blisters impede their efforts to breastfeed their babies. While the repetitive sucking motion of breastfeeding might cause these blisters to stay on the lip, they are only unsightly and not harmful.BottlesLip blisters, while more common in breastfed babies, can occur in bottle-fed babies as well. So, mothers do not need to turn to expressed milk if their baby has a lip blister. The same sucking motion that babies use to get milk from the breast they use to get milk from the bottle. However, the flow of milk is faster through the bottle, requiring less vigorous sucking and, thus, decreasing the likelihood of developing a lip blister. If one does develop in a bottle-fed baby, no treatment is necessary.