Lactose intolerance is a condition in which the intestine does not digest lactose in food and causes diarrhea or worsens existing diarrhea symptoms. Lactose intolerance secondary to diarrhea is more common in infants and can prolong diarrhea. Lactose intolerance is generally considered to be present in children with diarrhea lasting 7 days or more. The question of what treatment is appropriate for children with lactose intolerance after acute diarrhea is unclear. Studies have shown that lactose-free formula or diet can shorten the duration of diarrhea and reduce symptoms compared with lactose-containing formula or diet. For children with lactose intolerance secondary to acute diarrhea, a more reasonable dietary treatment is: 1. Breastfeeders should continue breastfeeding and switch to a lactose-free formula when they have diaper rash or poor weight gain; 2. Formula feeders should use lactose-free formula for 3-4 weeks before transitioning to regular formula, which can be an effective treatment and prevent recurrent diarrhea symptoms.