Dehydration in children occurs when the body is significantly depleted of water and electrolytes at varying levels. Symptoms and signs of dehydration in children include thirst, lethargy, dry mucous membranes, decreased urine output, and when the child is severely dehydrated, alarming symptoms such as rapid heart rate, low blood pressure, and shock appear. Diagnosis of dehydration in children is based on history and clinical examination. Treatment involves oral or intravenous fluids to replace lost fluids and electrolytes.

Babies who are fed too much salt are at risk of kidney damage, high blood pressure, and even increased risk of heart disease. Therefore, it is not recommended to give salt to babies under 1 year of age by adding salt to their diet. After 1 year of age, parents can add small amounts of salt to their baby's diet.

Hypernatremia is a common electrolyte disorder defined as a serum sodium concentration exceeding 145 mmol/L. However, hypernatremia is not only a problem of sodium homeostasis but also involves a decrease in total body water, often occurring in the elderly, debilitated, or severely acutely infected.