What should you know about breast milk lactose intolerance?

Lactose is the main milk sugar and is present in breast milk regardless of what the parent eats. Lactose intolerance occurs when the small intestine does not make enough lactase to digest it. Undigested lactose can draw water into the bowel and be fermented by gut bacteria, leading to loose stools, wind, bloating or abdominal discomfort. These signs can overlap with normal infant stool patterns, fast milk flow, infection, or another feeding problem, so they do not establish the diagnosis by themselves.

Continue breastfeeding unless a clinician advises otherwise; removing dairy from the parent’s diet does not remove lactose from breast milk. Arrange an examination if diarrhoea is persistent, feeding is difficult, or growth is a concern. Keep a simple record of feeds, stools, vomiting, wet nappies and behaviour. Do not give lactase drops, lactose-free formula, or restrict your own diet without professional guidance, because unnecessary changes can affect nutrition and milk supply. A clinician may consider the baby’s age, history and examination before suggesting [Food Intolerance Testing](/treatments/diagnostics-and-screening/food-intolerance-testing/) or [Nutrition Counselling](/treatments/lifestyle-and-wellness/nutrition-counselling/).

Seek urgent medical help for a baby who is unusually sleepy, difficult to wake, refusing feeds, passing much less urine, or showing signs of dehydration. Blood in the stool, repeated vomiting, a swollen abdomen, breathing difficulty, or fever also warrants prompt assessment. For background, see [Lactose Intolerance](/conditions/lactose-intolerance/), [Diarrhoea](/symptoms/diarrhoea/), [Bloating](/symptoms/bloating/) and [Abdominal Pain](/symptoms/abdominal-pain/).

Could these symptoms reflect lactose intolerance, an infection, or a feeding issue? Is my baby hydrated and gaining weight as expected? Should I change anything about breastfeeding or supplementation?