Consequences of dehydration A loss of body water equivalent to about 1% of body weight is normally compensated within 24 hours. Thirst stimulates drinking, so intake is increased and there is also a reduction in water loss by the kidneys. If losses are greater than this, reductions in physical and cognitive performance may occur and there may be some impairment of thermoregulation and cardiovascular function Mild dehydration can cause symptoms such as thirst, headache, weakness, dizziness and fatigue and generally makes people feel tired and lethargic. Symptoms of moderate dehydration may include dry mouth, little or no urine, sluggishness, a rapid heartbeat and lack of skin elasticity. Severe dehydration is a life-threatening medical emergency, and is characterized by extreme thirst, no urine, rapid breathing, altered mental state and cold, clammy skin. Increasing levels of dehydration with fluid losses of more than 1% of body weight can lead successively to reduction in exercise performance and in the ability to control body temperature. With fluid deficits of 4% and more, severe performance decrements may be observed as well as difficulties in concentration, headaches, irritability and sleepiness, and increases in body temperature and in respiratory rates. Dehydration that causes a loss of 10% or more of body weight can be fatal. As dehydration progresses, the volume of water in the blood stream decreases, and blood pressure may fall. Cardiovascular function is impaired with increasing levels of dehydration, with a rise in heart rate and difficulties in maintaining the volume of blood that the heart delivers to the tissues. The heart pumps harder to maintain blood flow to the organs, but blood pressure may fall as the blood volume falls. Reduced blood flow to the skin and reduced levels of hydration keep the body from sweating and dissipating heat. Chronic dehydration can increase the risk of infection, particularly of the urinary tract. The kidneys and other major organs that receive a decreased blood flow may begin to fail. Kidney failure is a common occurrence, although it is reversible if it is due to dehydration and is treated early. Decreased blood supply to the brain may cause confusion, impairing both cognitive function and coordination.