If you're noticing blood in your baby's diaper, cow's milk allergy might be the reason—it's more common in newborns than many parents realize. The good news: it's usually temporary and harmless. If you're breastfeeding, try removing dairy from your own diet for a few weeks since milk proteins pass into breast milk. If your baby is formula-fed, your pediatrician may suggest switching to a special formula. Most babies will likely outgrow this by age one without any lasting problems. The key is talking to your pediatrician before making dietary changes, so you can confirm what's happening and get the right support for your family.