By Becky Bell

Water is absolutely necessary for survival. It makes up approximately 60 percent of the human body, with every system depending on water to function properly.

Thus, dehydration—or a lack of body water—has widespread repercussions.

While mild dehydration is easily remedied, severe dehydration is a serious condition that can lead to loss of consciousness, organ failure or even death.

This article discusses the common signs and symptoms of dehydration.

What Is Dehydration?

Water is constantly leaving your body, mostly through sweat, urine and stools. An adequate amount of water must be consumed to make up for this loss.

Dehydration occurs when more water is leaving the body than coming in. It can be caused by either a lack of fluid intake or excessive fluid loss.

Here are some of the common causes of dehydration:

• Vigorous exercise: Intense exercise leads to fluid loss through sweat. If fluids are not replaced by drinking water, you can become dehydrated.

• Exposure to heat: Heat can cause you to lose fluid through sweat. You may become dehydrated if you don't drink extra water when it's very hot outside.

• Vomiting and diarrhea: Vomiting and diarrhea both cause significant fluid loss that can lead to dehydration.

• Nausea: Many people don't feel like eating or drinking when they are nauseated. It's important to continue drinking water so you don't become dehydrated.

• Burns or skin infections: Water can be lost through severe burns and skin infections.

• Diabetes: When blood sugar levels are high, the body increases urine production to eliminate sugar from the body. This can lead to dehydration if this loss is not matched with an increase in water consumption.

• Fever: A fever may contribute to fluid loss through sweating.

Summary: 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.

1. Thirst

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 percent 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 percent 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.

4. Headaches

Dehydration may trigger headaches or migraines in some people (5, 15, 16).

One study found that a fluid loss of 1.4 percent 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 percent 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 percent 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.