True lactose intolerance is very rare in newborns
Signs that may suggest a problem after milk feeds include:
Frequent watery diarrhea
Bloating or a swollen belly
Excessive gas
Fussiness or crying during or after feeds
Poor weight gain
Diaper rash from frequent acidic stools
Vomiting after feeds
Symptoms that start soon after breastfeeding or formula feeding
Symptoms that improve when lactose is removed from the diet
A family history of lactose intolerance
A doctor may check for:
Stool acidity or reducing substances
Weight gain and feeding history
Other causes such as milk protein allergy, infection, or reflux
Seek medical care if the baby has:
Blood in stool
Signs of dehydration
Persistent vomiting
Fever
Poor feeding
Weight loss or failure to gain weight