Causes of a Swollen Breast in a Baby

A swollen breast is a common condition that occurs in babies, both male and female. One or both of a baby's breasts may become swollen, firm and lumpy within a week after birth. Although this condition may seem peculiar, the swollen breasts usually shrink within a few weeks or months of life. Understanding the causes of this condition helps ease concern for anxious new parents.

Mother’s Hormones

While in the womb, a baby is exposed to surging hormones that a mother produces during pregnancy. These hormones are passed along to the baby and remain within the baby after birth. Maintaining excess levels of hormones such as estrogen and androgens can cause the baby’s breasts to swell. Sometimes only one breast will swell. When there is no more exposure to the hormones, the breast tissue will begin to shrink and become flat. This may take days, weeks or a few months. A milky substance called “witches milk” may leak from the nipples but will cease after a few days or weeks.

Breast Buds


Swollen Nipples in a Newborn

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According to pediatrician and author Dr. Alan Greene, swollen breasts in babies can be due to breast buds or lumps under the nipples. These lumps are mature breast tissue that can even secret milk. Breast buds can occur in both male and female babies and will diminish over the first few months of life.


In very rare cases, the swollen breasts in a baby are due to mastitis, or an infection of the breast tissue. If the breast or nipple looks red, tender or has a colored discharge other than a milky substance and the baby has a fever, a pediatrician should exam the baby for infection. Parents are advised not to squeeze or massage the swollen breasts, for this will only cause irritation and may lead to an infection.

Breast Feeding


Breast Buds in Infants

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Breast feeding can contribute to the baby’s breasts swelling due to the continuance of the mother’s hormones passing to the baby. While breast feeding may also contribute to prolonged breast enlargement and baby milk production, temporary or permanent weaning is not recommended.