Dehydration occurs when more fluid is leaving the body than being consumed. Factors that decrease fluid consumption or increase fluid losses can contribute to dehydration.
Thirst is a craving for fluid that serves as an automatic reminder to drink water.
It’s often the body’s first indicator that it needs more water.
Interestingly, your body is equipped with a complex system for regulating fluid balance. Even a small change in fluid balance can trigger a sensation of thirst (1, 2, 3).
For most people, drinking when they’re thirsty is an effective method for staying hydrated.
However, there are some situations in which thirst might not be a reliable indicator of hydration status.
For example, older people may need to consciously manage their fluid intake, as your sense of thirst tends to decline with age (4).
In addition, you may need to drink beyond simply satisfying your thirst if you are sweating profusely. For example, intense exercise and exposure to high temperatures can cause you to lose a large amount of water through sweat.
In these situations, you may need to drink additional water to stay hydrated.
Summary: Thirst is the body’s first indicator of dehydration. For most people, responding to thirst effectively prevents dehydration.
2. Changes in the color or amount of your urine
Your urine can tell you a lot about your hydration status, since it accounts for the majority of the fluid that leaves your body.
Thus, controlling the amount and composition of urine is one way in which the body is able to maintain proper fluid balance.
Urine, which is produced by the kidneys, consists of both water and waste products that your body needs to eliminate.
If you are dehydrated, the kidneys conserve water by concentrating urine. This allows waste to be eliminated while retaining water for important biological functions (5).
Interestingly, urine’s concentration affects its appearance. If you’re well hydrated, your urine should be a clear, pale yellow color and nearly odorless (6, 7).
On the other hand, cloudy, dark yellow urine is a sign of dehydration. A honey-yellow color may indicate mild dehydration, while a deep, amber-yellow color with a strong odor can signal severe dehydration (8, 9).
In addition to controlling the concentration of urine, the kidneys can also conserve fluid by decreasing the amount of urine produced. In fact, if the body becomes severely dehydrated, the kidneys may stop making urine altogether.
However, urine output varies from person to person, so there is no set amount of urine you should be producing every day. If you notice a significant decrease in urine, you may be dehydrated (10).
Keep in mind that certain foods, medications and medical conditions can also influence the color and amount of urine. If your urine is consistently a color other than pale yellow, you should consult your doctor.
Summary: The color and amount of urine that your body produces are good indicators of your hydration status. Dark yellow urine or a low urine output are signs of dehydration.
3. Fatigue or sleepiness
Fatigue or tiredness can have many different causes, but dehydration can be one of them.
Many studies have shown that dehydration causes fatigue and decreases endurance during exercise (11, 12, 13).
For this reason, drinking an adequate amount of water is particularly important during exercise.
However, you don’t have to be exercising to experience dehydration-related fatigue.
Studies have shown that fluid loss amounting to 1–3% of your body weight, which is considered mild dehydration, can cause feelings of fatigue and sleepiness during normal daily activities.
In a study of young, healthy women, water restriction for 24 hours caused sleepiness, confusion, fatigue and decreased alertness.
All of these symptoms improved when the women were allowed to freely drink water at the conclusion of the 24-hour period (9).
Another study in men found that a fluid loss amounting to 1.6% of their body weight significantly increased fatigue both at rest and during exercise (14).
This amount of fluid loss can easily occur during normal daily activities if you’re not drinking an adequate amount of fluid throughout the day.
Summary: Fatigue or sleepiness can be a sign of dehydration. Drinking water may boost your energy and help you feel more alert.
Dehydration may trigger headaches or migraines in some people (5, 15, 16).
One study found that a fluid loss of 1.4% of body weight caused headaches and moodiness in healthy women (17).
Another study found similar results in men. Water restriction for 37 hours, which resulted in a 2.7% fluid loss, led to headaches and difficulty concentrating (18).
Fortunately, evidence shows that headaches caused by dehydration can be relieved by drinking water.
In one small study, all but one of 34 people who experienced a dehydration-related headache found relief from drinking water.
In fact, drinking water provided headache relief within 30 minutes for 22 out of 34 people, while 11 other participants found relief within three hours (16).
Keep in mind that there are many different types of headaches, and they are not all caused by a lack of hydration.
Nevertheless, a headache may be a sign that your body needs more water.
Summary: Dehydration can cause headaches. In most cases, drinking water can resolve a dehydration-related headache.
5. Changes in skin elasticity
Dehydration can cause changes to the appearance and texture of your skin.
Your skin is made up of approximately 30% water, which is responsible for its fullness and elasticity (5).
Healthy, well-hydrated skin will return to its normal shape after being pulled and stretched. This elastic nature of skin is known as skin turgor.
On the other hand, when the body is dehydrated, fluid is pulled away from the skin and diverted to major organs to keep them functioning properly. This shift of fluid away from the skin causes it to lose its elasticity.
To test the elasticity of your skin, pinch your skin between your thumb and your forefinger.
If you are well hydrated, your skin should snap back immediately after being released. If it takes a half a second or more for your skin to return to its shape, you may be dehydrated (5, 19, 20).
In addition, a lack of fluid in the skin can cause dryness and make skin feel cool and clammy to the touch.
Summary: Decreased skin turgor, or elasticity, is a sign of dehydration. Skin that is dry, cool and clammy may also indicate dehydration.
6. Muscle cramps
Muscle cramps may be a sign of dehydration. Cramps are particularly common when dehydration is caused by excessive sweating.
Interestingly, sweating can result in a significant loss of both fluid and sodium, which is an electrolyte that plays a role in muscle contractions.
Thus, when fluid and sodium become depleted, muscles sometimes contract involuntarily. This is known as a muscle cramp (21).
For this reason, adequate hydration is especially important during strenuous exercise or exercise in high temperatures.
Summary: Fluid and sodium depletions can lead to muscle cramps. Drinking water is particularly important during strenuous exercise.
7. Decrease in blood pressure
Low blood pressure can be a symptom of dehydration (22).
Dehydration lowers the volume of blood in the body, which lowers the pressure on artery walls (5, 23).
Interestingly, low blood pressure might make you feel light-headed or dizzy when you go from lying down to standing up (24).
That’s because your heart has to pump faster and harder to get blood to the brain when there is less fluid in the body. When you stand up, it may take a few seconds for blood to get to the brain from the lower limbs.
What’s more, low blood pressure can make you feel weak and tired.
Nevertheless, a small drop in blood pressure is relatively harmless and usually remedied by drinking water (25).
On the other hand, severe dehydration can lead to dangerously low blood pressure. Symptoms like blurred vision, nausea and fainting could indicate very low blood pressure that requires medical attention (24).
Summary: Dehydration can cause a drop in blood pressure, which might make you feel light-headed, weak and tired. Severe dehydration can cause dangerously low blood pressure that requires medical attention.
8. Rapid heart rate or heart palpitations
Dehydration can cause a rapid heart rate or heart palpitations. Palpitations give you the feeling that your heart is jumping or skipping a beat.
Interestingly, these abnormalities are a result of the heart attempting to compensate for the lack of fluid in the body.
When there’s not enough fluid in your body, it decreases the volume of blood in your blood vessels. Your body then works hard to deliver enough blood to your organs by increasing its heart rate, pumping blood more quickly throughout your body (5, 26).
When this happens, you might feel your heart racing, fluttering or pounding extra hard.
Fortunately, in most cases of dehydration, this increase in heart rate effectively makes up for the low blood volume. Even with less blood pumping through the body, the organs and tissues are able to receive what they need.
However, as dehydration becomes more severe, the heart becomes less effective at compensating for the lack of fluid. If the heart is unable to get blood to the organs, they will eventually shut down.
Keep in mind that dehydration is not the only condition that affects heart rate. Rapid heart rate or palpitations can also indicate a more serious medical condition.
That being said, if your heart rate does not return to normal after drinking water, you should consult a medical professional.
Summary: A lack of fluid in the body decreases blood volume. The heart makes up for the lack of blood volume by working harder and faster to pump blood throughout the body.
9. Irritability or confusion
Dehydration can have a significant effect on brain function.
Studies have shown that even mild dehydration can cause irritability and decreased brain function (10, 27).
A few studies found that a 1–2% loss of body fluid causes symptoms, such as anxiety, moodiness, difficulty concentrating and a decline in short-term memory (14, 28).
Furthermore, brain function can deteriorate significantly as dehydration becomes more severe. Severe dehydration can cause confusion and incoherence (29).
In fact, confusion and even delirium are common symptoms among older adults who are dehydrated. Older adults are particularly susceptible to becoming dehydrated due to their sense of thirst declining with age (30, 31, 32).
Conversely, drinking plenty of water has a positive effect on mental clarity and brain function. In fact, both children and adults have been found to perform tasks better when they are well hydrated (33, 34, 35).
In one study, children who were given additional water to drink had improved short-term memory and performed better in school (33).
Overall, it appears that hydration status can have a significant impact on mental performance.
Summary: Dehydration can negatively affect brain function and cause symptoms like moodiness, anxiety, decreased concentration and confusion.
10. Serious complications and organ failure
Severe dehydration can lead to very serious complications.
Every organ in the body requires fluid to function properly. If dehydration becomes critical, organs will begin to shut down.
In fact, a severe loss of body fluid can lead to shock, which is a potentially fatal condition (36).
Shock occurs when the volume of blood becomes so low that the brain and other organs are not able to receive the oxygen they need (37).
Moreover, shock can cause complications like loss of consciousness, brain damage, kidney failure and heart attack. If shock is not treated immediately, it will result in death (38).
That being said, shock is a rare consequence of dehydration that only occurs with an extreme loss of body water. It is most likely to come about when fluid is lost through trauma, severe burns or prolonged vomiting and diarrhea.
Summary: Extreme dehydration can cause shock and organ failure. This level of dehydration can be fatal if not treated immediately.
How to prevent dehydration
The key to preventing dehydration is to drink plenty of water throughout the day, along with other beverages like unsweetened coffee and tea.
Interestingly, water-rich foods like fruits and vegetables also contribute to hydration.
However, there’s no magic amount of fluid you should drink every day to stay hydrated (39).
Fluid requirements vary from person to person and are affected by activity level, amount of sweat and climate (40).
Nevertheless, here are some tips to stay hydrated:
- Drink when you are thirsty: For most people, thirst is a reliable indicator that your body needs water. If you feel thirsty, drink water (1).
- Drink plenty of water before exercising: It’s important to be properly hydrated before you start exercising, particularly if you are going to be active in the heat.
- Replace fluids lost through sweat: If you sweat a lot, you will need to drink extra water to replace lost fluids. In this case, you may need to drink more than your thirst demands (12).
- Keep tabs on the color of your urine: The color of your urine is a good indicator of your hydration status. Drink enough water so that your urine maintains a pale yellow color.
- Replace fluids lost through vomiting or diarrhea: Sip on liquids or ice chips if you are experiencing vomiting or diarrhea. If you are unable to keep fluids down for more than 24 hours, seek medical attention.
Summary: In order to prevent dehydration, drink when you are thirsty and replace fluids lost through sweat or illness.