Dehydration

Your body needs water to stay healthy.

You lose water when you sweat. You also lose water when you breathe.

If you do not drink enough, you might get thirsty. You may also feel very tired or dizzy.

This is called dehydration.

Hot weather can make you lose water fast. Moving a lot also uses up your water. Some people, like babies, must be extra careful.

Eating food can help you get water too. Most people can fix small problems by drinking.

It is good to listen to your body. Drinking water helps you feel your best.

Your body is mostly made of water. Most people have about 60% water in them.

Dehydration happens when you lose more water than you drink. You lose water when you sweat or breathe. You also lose water through urination. Some people lose water fast. This can happen during sports or in hot weather.

Small losses of water can make it hard to think. If you lose 5% to 8% of your water, you might feel dizzy. You might also feel very tired. Losing more than 10% can cause confusion. Severe cases can be very dangerous.

Your body has a way to fight this. A part of your brain detects when water is low. It lets out a hormone called ADH. This hormone helps your kidneys save water.

Doctors can check for dehydration. They might look at your skin. They can also test your urine.

Most people can fix mild dehydration by drinking water. Some people may need fluids through a tube in their vein. This is called intravenous therapy. Eating food also helps you get water.

Dehydration is a serious condition that happens when your body loses more water than it takes in. Water is vital because it helps all your metabolic processes, which are the many ways your body stays alive. Most people have about 60% water in their bodies. This water is found in two places: inside your cells and outside them in your blood and other fluids.

When you lose too much water, these levels get out of balance. This can make it very hard for your body to work correctly.

Your body has a clever way to fight water loss. When you lose water, the concentration of things like salt in your blood goes up. This is called higher serum osmolarity. Special sensors in your brain, called osmoreceptors, detect this change. They tell your body to release a hormone called antidiuretic hormone, or ADH. This hormone tells your kidneys to absorb more water back into your body instead of letting it leave as urine.

In very serious cases, ADH also helps tighten your blood vessels to keep your blood pressure up.

Scientists and doctors have studied how different amounts of water loss affect people. Losing just 1% to 2% of your body water can make it harder to think clearly. If you lose 5% to 8%, you might feel dizzy or very tired. Losing over 10% can cause physical and mental problems, along with extreme thirst.

If a person loses 15% to 25% of their body water, it can lead to death. This shows why keeping a steady balance of water is so important for survival.

Many things can cause you to lose water quickly. You might sweat a lot during heavy exercise in hot or humid weather. Some people lose water through vomiting or diarrhea. Even breathing and your skin can let water escape without you noticing.

Certain groups of people are at higher risk, such as infants, children, and the elderly. Older adults may also feel less thirsty even when they need water. This makes it harder for them to know when they are becoming dehydrated.

Doctors use several ways to see if someone is dehydrated. They might perform a skin turgor test by pinching the skin to see how fast it snaps back. They can also look for sunken eyes or dry skin.

Laboratory tests are also used to check blood and urine. For example, a urinalysis might show that urine is a darker color or has a strong smell. Most mild cases are fixed by drinking water or eating food, which provides about 22% of our water intake. Severe cases may require fluids through a tube in a vein, called intravenous therapy.

Dehydration is a physiological state defined by a lack of total body water. This deficiency disrupts metabolic processes, which are the chemical reactions that sustain life. Water is essential for maintaining homeostasis, the stable internal environment of the body. In humans, water content varies significantly based on age and body composition. Newborns typically have a water content of 70% to 75%. An average adult carries about 60% water, though this can drop to 40% or less in obese adults.

To understand dehydration, one must look at how water is distributed. Water is classified into two main groups: intracellular fluid and extracellular fluid. Intracellular fluid is the water contained within the cells, making up about 57% of total body water. This fluid has high concentrations of proteins, phosphate, magnesium, and potassium. Extracellular fluid stays outside the cells and accounts for 43% of total body water. This includes blood plasma and interstitial fluid. The most common ions in extracellular fluid are sodium, chloride, and bicarbonate.

Dehydration occurs when free water loss exceeds the amount of water a person consumes. Water is lost through both sensible and insensible processes. Sensible loss includes visible outputs like sweating, vomiting, and diarrhea. It also includes osmotic diuresis, where the kidneys excrete more water. Insensible loss occurs more quietly through the respiratory tract and the skin. Many factors increase these losses, such as high altitudes, endurance athletics, or hot and humid weather. In men, sweat loss during intense exercise can exceed 2 L/h, and even reach 3–4 L/h in extreme heat.

The body uses a complex mechanism to combat water loss. When water levels drop, the concentration of solutes in the blood increases. This increase is known as higher serum osmolarity. Specialized sensors in the hypothalamus called osmoreceptors detect this change. In response, the hypothalamus triggers the release of antidiuretic hormone (ADH). ADH acts on V2 receptors in the collecting tubule of the nephron within the kidneys. This increases the expression of aquaporin, which helps the kidneys absorb more water back into the body.

In more severe cases, the body employs further emergency measures. If blood pressure becomes dangerously low, the hypothalamus releases higher amounts of ADH. This hormone then acts on V1 receptors. This action causes contractions in the peripheral vascular smooth muscle. These contractions increase systemic vascular resistance, which helps raise blood pressure. It is important to distinguish dehydration from hypovolemia. Hypovolemia specifically refers to a decrease in the volume of blood plasma. While related, they are regulated through independent biological mechanisms.

The severity of dehydration is measured by the percentage of body water lost. A loss of 1% to 2% is considered mild and can impair cognitive performance. A decrease of 5% to 8% often causes dizziness and fatigue. If a person loses more than 10% of their body water, they may experience physical and mental deterioration along with severe thirst. Extremely high levels of loss, between 15% and 25%, can lead to death.

Symptoms can include headaches, nausea, confusion, seizures, and sunken eyes.

Medical professionals use various methods to diagnose and treat this condition. Doctors may use a skin turgor test by pinching the skin to see how quickly it returns to its normal position. They also look for dry mucous membranes or increased capillary refill time.

Laboratory tests, such as urinalysis, can reveal darker urine or higher sodium levels. Mild dehydration is usually treated with oral rehydration. Severe cases may require intravenous (IV) therapy to replace fluids directly in the veins. However, doctors must be careful; injecting pure water into the veins can cause red blood cells to undergo lysis, or bursting.