Dehydration occurs when you use or lose more fluid than you take in, and your body doesn't have enough water and other fluids to carry out its normal functions. If you don't replace lost fluids, you will get dehydrated. Anyone may become dehydrated, but the condition is especially dangerous for young children and older adults.
The most common cause of dehydration in young children is severe diarrhea and vomiting. Older adults naturally have a lower volume of water in their bodies, and may have conditions or take medications that increase the risk of dehydration. This means that even minor illnesses, such as infections affecting the lungs or bladder, can result in dehydration in older adults. Dehydration also can occur in any age group if you don't drink enough water during hot weather — especially if you are exercising vigorously.
You can usually reverse mild to moderate dehydration by drinking more fluids, but severe dehydration needs immediate medical treatment. Thirst isn't always a reliable early indicator of the body's need for water. Many people, particularly older adults, don't feel thirsty until they're already dehydrated. That's why it's important to increase water intake during hot weather or when you're ill. Sometimes dehydration occurs for simple reasons: You don't drink enough because you're sick or busy, or because you lack access to safe drinking water when you're traveling, hiking or camping.
To prevent dehydration, drink plenty of fluids and eat foods high in water such as fruits and vegetables. Letting thirst be your guide is an adequate daily guideline for most healthy people.
Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. Check out these best-sellers and special offers on books and newsletters from Mayo Clinic Press. On this page. Risk factors. The signs and symptoms of dehydration also may differ by age. Infant or young child Dry mouth and tongue No tears when crying No wet diapers for three hours Sunken eyes, cheeks Sunken soft spot on top of skull Listlessness or irritability.
