Lactose intolerance refers to a condition caused by a deficiency of lactase, leading to an inability to fully break down the lactose in human or cow's milk, which results in symptoms such as diarrhea. It is most commonly seen in infants and young children whose main diet consists of dairy products. The primary symptoms are diarrhea, and some patients may also experience vomiting and intestinal cramps. In terms of treatment, one can stop consuming human or cow's milk and switch to lactose-free formula milk or soy milk instead. Additionally, consuming fermented milk is also an option, because the lactose in cow's milk or human milk can be converted into lactic acid through fermentation, thus preventing the symptoms of lactose intolerance.