Breast milk lactose intolerance is a condition in which the baby lacks the enzyme lactase in the mucous membrane of the small intestine, resulting in impaired digestion and absorption when milk is taken, thus causing symptoms of gastrointestinal discomfort. Congenital lactase deficiency is related to heredity. Common clinical symptoms include diarrhea, abdominal distension, hyperactive bowel sounds, and in severe cases, frequent vomiting, leading to water loss and metabolic acidosis. Children with breast milk lactose intolerance are best seen in a regular pediatric hospital, where they can be given lactase supplementation under a doctor’s supervision. If the symptoms are not serious, try breastfeeding in small amounts and avoid feeding on an empty stomach.