The body will attempt to deal with dehydration by first stimulating the thirst centres of the brain, which will prompt someone who is dehydrated to drink more fluid. However, if water intake cannot keep up with water loss, dehydration will become severe and the body will respond by doing things that decrease the loss of water, such as decreasing sweat and producing less urine. People who are adequately hydrated will usually urinate light-coloured urine every 3 to 4 hours.
Symptoms of mild to moderate dehydration include thirst, reduced sweating, decreased urine production, dry mouth, dizziness, and reduced skin elasticity.
Because the water in the bloodstream is very important, the water in and around the cells will begin to move into the bloodstream. If dehydration continues, the cells in the body will begin to shrivel and malfunction, and tissues in the body will begin to dry out. Because brain cells are among the most vulnerable to dehydration, confusion and even coma can occur.
With severe dehydration, the body's electrolytes may become deficient, and water will not be able to move as easily from inside the cells out into the blood. The amount of water in the bloodstream will be further decreased and blood pressure can drop, causing lightheadedness or the feeling of starting to faint, particularly when standing up suddenly. If water and electrolyte losses continue, blood pressure can fall dangerously low and result in shock and severe damage to many internal organs, such as the kidneys, liver, and brain.
Dehydration is a serious problem in young children and infants because they are more sensitive to fluid loss, and it can occur even after a few hours of vomiting, diarrhea, or profuse sweating.
If a baby is dehydrated, there may be:
- an absence of tears during crying
- a dry mouth
- excess sleepiness
- a sunken soft spot on the top of the head
- fewer wet diapers
- sunken eyes