This Is Why Your Baby's Breath Smells Sour

On the more serious side of things, sour smelling breath could be a sign of gastroesophageal reflux. This type of reflux is harder to diagnose because, as Today's Parent warns, it's not often accompanied by spitting up. It will, however, make your baby fussy and irritable. 

Their tiny digestive systems aren't as fully developed as ours, so their stomachs get full much more rapidly. Babies also spend most of their time lying on their backs, which contributes to this kind of reflux. As Dr. Sears advises, gastroesophageal reflux causes painful stomach acids to be regurgitated into the esophagus, leading to what we would commonly refer to as heartburn. It can even lead to wheezing or asthma, as well as frequent night-waking, writhing around, and intense crying (more than the typical variety). 

You should consult your doctor if concerned this is the cause of your baby's sour breath, as medication may be required to treat it, but there are some home remedies you can try to ease discomfort. This includes keeping your baby upright for at least half an hour after feeding, feeding in smaller, more frequent increments, and wearing a carrier more often, as babies tend to reflux while crying. A considerable percentage of babies experience reflux during the first three months of their lives, so don't worry, as they'll typically outgrow it as they get older, but if you have concerns, bring it up with your child's doctor.