The dangers of hydronephrosis mainly include secondary infection, causing kidney stones, kidney failure and increasing the chance of kidney trauma. 1. Secondary infection: hydronephrosis leads to urine retention in the kidney and ureter, which is easy to cause bacteria breeding and infection. Secondary infection may lead to pyelonephritis, and in serious cases, it may cause bacteremia or septicemia. 2. Causing kidney stones: long-term fluid retention in the kidneys can’t expel the excess calcium from the body in time, which gradually accumulates and leads to the formation of kidney stones, and may aggravate the degree of infection of hydronephrosis again, forming a vicious circle and causing serious impacts. 3. Causing kidney failure: long-term hydronephrosis may also lead to increased pressure in the kidney, compressing the renal tubules, glomeruli and nearby blood vessels, leading to ischemia and hypoxia of renal tissues, and ultimately causing kidney failure. 4. Increase the chance of kidney injury: hydronephrosis gradually increases with the development of the disease, which may lead to weak renal cortex and increase the chance of kidney injury when hit by external force. There may be other hazards of hydronephrosis. When patients are diagnosed with hydronephrosis, it is recommended that they go to regular hospitals in a timely manner and receive standardized treatment under the guidance of doctors.