My baby has white patches on the insides of her cheeks. My baby has white patches on the insides of her cheeks. It's most common in babies 2 months and younger, but it can appear in older babies, too.
Most infants first come in contact with yeast as they travel down the birth canal.
Thrush develops when hormonal changes right after birth trigger an overgrowth of yeast in your baby's mouth. If your baby is on antibiotics for any reason, this could be the root of the problem. Note that your baby can pass his thrush on to you if you are breastfeeding, resulting in a painful infection that will need a doctor's treatment. And you can trigger a case of thrush in your baby if you're breastfeeding and taking antibiotics to treat an infection. If you think your baby has thrush, look for the characteristic white patches.