Common dehydration symptoms include thirst, dark yellow urine, peeing less often, dry mouth, headache, fatigue and dizziness. Dehydration happens when you lose more fluid than you take in, and you lose minerals along with it. Even mild dehydration can affect how you feel: in one study, young women who lost about 1.4% of their body water reported worse mood, more headaches and more trouble concentrating (Armstrong et al., 2012).
10 signs of dehydration
- Thirst. Often a late sign, especially in older adults, whose sense of thirst weakens with age.
- Dark yellow urine. Pale straw-colored urine is the goal.
- Peeing less often than usual.
- Dry mouth, lips or skin.
- Headache.
- Fatigue or low energy.
- Dizziness or lightheadedness, especially when you stand up.
- Brain fog or trouble concentrating.
- Muscle cramps, often a sign you're low on minerals as well as water.
- Feeling irritable or in a low mood.
Symptom list based on MedlinePlus.
When dehydration is an emergency
Get medical help right away for confusion, fainting, a very fast heartbeat, not peeing for 8 hours or more, a high fever, or vomiting or diarrhea that won't stop. Babies, young children, older adults and people with chronic illness can become dehydrated quickly and need extra care.
Common causes of dehydration
- Sweating from exercise, heat, sauna or physical work. See Sauna and Cold Plunge
- Not drinking enough, especially busy workdays
- Illness with fever, vomiting or diarrhea. See Electrolytes When You're Sick
- Alcohol, which makes your kidneys release more fluid
- Air travel. See Electrolytes for Flying
How to rehydrate the right way
When you're dehydrated, you're usually low on sodium and other electrolytes too, not just water. Rehydrating with water plus electrolytes helps your body hold on to the fluid instead of flushing it straight through. Sip steadily rather than chugging, and add a salty snack or broth if you can. Learn more in What Are Electrolytes?
Can you overdo it? Yes. Drinking huge amounts of plain water can dilute your sodium. See Can You Drink Too Much Water?
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Frequently asked questions
What are the first signs of dehydration?
Thirst, dark yellow urine, dry mouth and a mild headache are usually first.
Can dehydration cause headaches?
Yes. Headache is one of the most common symptoms, even with mild dehydration.
How long does it take to rehydrate?
Mild dehydration often improves within an hour or two of drinking fluids with electrolytes. Severe dehydration needs medical care.
Is water enough to rehydrate?
For mild cases, often. After heavy sweating, illness or alcohol, adding electrolytes helps your body hold on to the fluid.
Can you be dehydrated without feeling thirsty?
Yes, especially older adults and people who are busy or distracted.