Acute lead poisoning can result in abdominal discomfort, nervous system damage, and encephalitis. Chronic exposure is characterized by a blue line on the gums and can lead to damage to the brain, kidneys, nervous system, and red blood cells. Even low levels can contribute to hypertension in older people or to "silent lead poisoning" in exposed children, which affects the developing brain and leads to visual-motor problems and lowered intelligence. Lower doses may be treated by altering the diet to counteract lead's effects and and cleaning the person's environment to reduce intake. Higher doses are treated with chelating agents, drugs that remove lead from the body. Symptoms recur upon subsequent exposure.