Answer: The scent is most often a reflection of how long the poop was in the intestines -- the longer it sits in bacteria, the more it'll smell. However, some babies with very sour- or foul-smelling poop may have an intolerance or allergy. In general, breastfed baby poop doesn't stink at all, while that from formula-fed infants is just lightly odorous. Those early poopy diapers really shouldn't clear the room. However, once you add baby food, and then various protein sources, it's another story. If you think your baby's BMs are exceptionally smelly, talk with your pediatrician.