Diarrhea in infants, especially rotavirus infected diarrhea, can cause destruction of the intestinal mucosa, resulting in secondary lactose intolerance, which in turn can aggravate diarrhea, leading to a vicious cycle of prolonged diarrhea. Lactose deprivation diet is an important treatment for secondary lactose intolerance. Diarrhea in infants is a common clinical disease in pediatrics. The loss of nutrients and intestinal dysfunction during diarrhea can easily lead to various complications and affect the healthy growth of infants. Disorders of fluid balance Fluid balance is an important condition for maintaining normal physiological functions. Since infants are relatively immature in fluid regulation, disorders of water-electrolyte and acid-base balance are more likely to occur during diarrhea. Fluid imbalance is very dangerous and should be detected and corrected in time. Dehydration is the most frequent fluid imbalance. In severe cases, electrolytes are lost along with body fluids, the most common one being hypokalemia. Hypokalemia is the most common cause of hypokalemia, which can lead to muscle weakness, cardiac arrhythmias and renal impairment. In addition, calcium (magnesium) ions are also lost from the stool during diarrhea, and hypocalcemia occurs. Metabolic acidosis is also a complication of severe diarrhea, which is caused by the loss of large amounts of alkaline substances due to diarrhea and the accumulation of acid in the body and impaired acid excretion. Infants may show symptoms such as depression, deep and rapid breathing and exhalation of acetone-smelling gas. Malnutrition Malnutrition can result from prolonged or chronic diarrhea. In addition to the loss of a large amount of nutrients during diarrhea, long-term diarrhea can disrupt the normal digestive and absorption environment of the infant’s intestines, resulting in impaired absorption of nutrients, thus causing malnutrition, which in turn causes atrophy and degeneration of the gastrointestinal mucosa, further affecting the digestion and absorption of nutrients, forming a vicious circle. Therefore, we should actively search for the causes of diarrhea and treat them, while paying attention to dietary adjustment to ensure sufficient calories and nutrients. Diarrhea in infants is one of the major contributing factors to the development of intestinal entrapment. Diarrhea causes disturbance of intestinal peristalsis, and low potassium causes weakening of intestinal smooth muscle dynamics, especially viral diarrhea can cause edema and congestion of the intestinal wall, ileal lymph node hyperplasia and local intestinal wall thickening, which leads to the occurrence of intussusception. Intussusception is a life-threatening emergency, and clinicians should be highly alert to the sudden appearance of crying, restlessness, abdominal distension, vomiting, etc. in children with diarrhea and ultrasound for a clear diagnosis.