That headache you have right now? You might be blaming your screen or a bad night’s sleep. That dizzy spell when you stood up? Your brain probably went straight to worst-case scenarios.
Sometimes the answer is simpler. You just need more water.
Two doctors who spend their careers thinking about how the body handles fluids sat down to explain what dehydration actually looks like and what to do about it. Mitchell Rosner, MD, is a nephrologist who specializes in fluid and electrolyte disorders. James Winger, MD, is a sports medicine physician who studies how the body manages fluids during exercise. They shared their expertise with Reader’s Digest.
What happens when you’re dehydrated?
As your body loses fluid, it has to work harder to keep things running. Dr. Rosner says dehydration can reduce blood volume and lower blood pressure, forcing the heart to beat faster. Losing fluid and electrolytes can also lead to muscle cramps and make it harder for your body to cool itself down.
Severe dehydration, when fluid losses go without replacement for too long, can eventually affect the kidneys, brain, and cardiovascular system, Dr. Rosner says.
The quick skin test worth trying
You may have heard of the skin-pinch test, also called the skin-turgor test. It checks how quickly your skin snaps back after you gently pinch it.
According to MedlinePlus, the consumer health service of the National Library of Medicine, you pinch the skin on the back of your hand, your abdomen, or upper chest for a few seconds and then let go. Normally, the skin returns to place quickly. If it is slow to bounce back, that can be a sign of moderate to severe fluid loss.
Here is the catch, though, and this matters for our generation. Dr. Rosner says the test becomes less reliable in adults over 65 because skin naturally loses elasticity as we age. That means the skin can recoil slowly even when hydration is perfectly fine. Dr. Winger calls it “extremely unreliable,” noting that age, disease, and the underlying condition of someone’s skin can all affect the result.
Try it if you are curious. Just do not rely on it alone. Pay attention to the full picture your body is giving you.
The symptoms that tell the real story
Rather than relying on any single clue, look for a pattern. Here is what dehydration can look like:
- Thirst: One of your body’s built-in early signals that it is time to drink.
- Dry or sticky mouth: Another early sign that fluids are running low.
- Darker urine: More concentrated urine tends to look darker. Keep in mind that medications and vitamins like B-complex and carotene can also affect color.
- Going to the bathroom less often: Your body may be conserving fluid.
- Headache: Dehydration can trigger one, though headaches have many causes; context matters.
- Fatigue or brain fog: Feeling unusually tired or unfocused can show up with dehydration.
- Dizziness: Fluid loss can affect blood volume and blood pressure, leaving you lightheaded.
- Rapid heartbeat, confusion, or fainting: These can signal more significant dehydration and deserve immediate medical attention.
One thing worth knowing: clear urine does not automatically mean you are perfectly hydrated. Dr. Rosner says urine color is highly variable and hydration is just one of many factors that affect it. Darker urine is worth noticing, but do not assume dehydration is the only possible reason.
If you feel thirsty, is it already too late?
Not at all. Dr. Rosner says thirst kicks in early in the dehydration process. It is your body’s early warning system doing exactly what it is supposed to do.
Dr. Winger explains that when you lose water, the concentration of fluid in your blood rises. The hypothalamus senses that change and triggers hormonal responses that help the kidneys hold onto water, all of this happening well before major fluid loss occurs. “Healthy adults can safely rely on thirst to gauge their fluid needs,” Dr. Winger says.
That said, a 2023 review published in Nutrients found that older adults are especially vulnerable to dehydration, in part because aging can affect the systems that control thirst and fluid balance. So when you feel thirsty, drink. It is not a sign you have failed some hydration test. It is just your body talking to you.
Is dehydration only a summer problem?
It is easy to assume dehydration is strictly a hot-weather problem. Dr. Winger says that is a misconception. “Dehydration can occur in any weather in which fluid losses are not adequately met with fluid replacement,” he says.
Heat raises the stakes. The CDC notes that dehydration is an important risk factor for heat-related illness. But a cold morning walk or a bout of illness in January can leave you just as low on fluids. What changes is how obvious the need to drink feels. A scorching summer day practically reminds you to reach for a glass. A brisk fall afternoon may not.
If you are losing more fluid than you are replacing, it can happen in any season.
Can drinking too much water cause problems?
It can. Dr. Rosner says drinking too much water can dilute sodium in the blood and cause a condition called hyponatremia, which can become life-threatening. He also says the familiar “eight glasses a day” rule does not apply equally to everyone; individual fluid needs vary.
Not all of your fluid has to come from a glass, either. Water-rich foods, including fruits, count toward your intake too, Dr. Rosner points out.
When is it time to call the doctor?
Dr. Winger says when dehydration progresses to the point that the body cannot pump enough blood to its organs, those organs begin to show signs of dysfunction. This can affect the brain, heart, kidneys, liver, and more. Dr. Rosner says severe dehydration can lead to extreme sleepiness, kidney failure, seizures, or low-blood-volume shock.
According to MedlinePlus, signs that warrant immediate medical attention include confusion, fainting, rapid heartbeat, rapid breathing, the inability to urinate, and shock symptoms such as pale skin, a weak pulse, cold hands and feet, sweating, and loss of consciousness.
At that point, put down the glass and get help. The skin-pinch test can wait.
