Dehydration is caused by an inadequate intake of water to make up for the amount of water lost from the body. The severity of dehydration depends on various factors including age, body weight, physical activity level, general state of health and the climate.

The two main types of dehydration are isotonic dehydration and hypernatremic dehydration.

Isotonic dehydration
In this form of dehydration, water and sodium are lost from the extracellular fluid in equivalent amounts and there is no osmotic movement of water from the inside of cells to the outside. Isotonic dehydration is often caused by diarrhea, vomiting or inadequate intake of fluid.

Hypernatremic dehydration
Most commonly seen in infants, hypernatremic dehydration describes a loss of water that is greater than the amount of sodium lost, leading to a rise in blood sodium or hypernatremia. The condition is commonly seen in cases of pediatric dehydration caused by diarrhea.

Causes of dehydration

Gastrointestinal causes
Diarrhea and vomiting due to gastroenteritis, cholera, shigellosis, Yellow fever or infection of the gastrointestinal tract may lead to a loss of fluids, essential nutrients and minerals. This leads to dehydration as well as an electrolyte imbalance. Stomach upsets can also restrict the ability to hold water down, meaning fluid loss is increased while fluid intake is reduced.
 

Sweating
Excessive sweating due to vigorous exercise, sports, fever or heavy manual work, especially in hot and humid climates, can also cause excessive fluid loss and dehydration. In these situations, it is essential to keep drinking fluids to replace those that have been lost. Children and teenagers are at an increased risk of dehydration risk because they are less able to recognize the symptoms and correct it with fluid intake than older people are.

Alcohol intake
Dehydration can also occur as a result of drinking excessive amounts of alcohol. Alcohol itself is a diuretic and stimulates urination. Headaches that occur after excessive alcohol intake are often indicative of dehydration.

Diabetes
Diabetes can lead to dehydration. When blood sugar levels are raised for long periods, the kidneys start to remove glucose through urinary excretion, which also removes water from the body.

Blood loss
Excessive blood loss can also result in dehydration. This is called hypovolemia or low blood volume.

Burns
Burns can deplete water from the body, leading to dehydration, especially in cases of severe burns. Shock can be another contributor to dehydration in burns victims.