This is general information, not medical advice or a way to diagnose yourself. Dehydration can become serious, especially in babies, young children, older adults and people with medical conditions. If you are worried about your health or someone else’s, contact a doctor or local emergency services.
What dehydration means
Dehydration happens when the body loses more fluid than it takes in. It is common and often mild, and it is easy to correct in many cases. It can result from not drinking enough, but also from sweating heavily, fever, vomiting, diarrhea, or some medicines and conditions that increase fluid loss.
Dehydration exists on a spectrum, from mildly short of fluid to a medical emergency. Signs can overlap with many other problems, so they are clues rather than proof.
Common signs of mild dehydration
In adults, mild dehydration is often associated with:
- Thirst and a dry or sticky mouth
- Darker yellow urine than usual, or passing urine less often
- Tiredness or low energy
- Headache
- Lightheadedness, especially when standing up
- Dry lips or skin
- Muscle cramps
Thirst is a useful clue for most healthy adults, though it is not always reliable. By the time you notice a strong thirst, you may already be somewhat short of fluid. Older adults may feel thirst less strongly.
Signs that can point to more serious dehydration
Some symptoms suggest the problem may be more than mild:
- Very dark urine, or hardly any urine for many hours
- Dizziness that does not settle, or fainting
- A fast heartbeat or rapid breathing
- Confusion, unusual irritability or extreme sleepiness
- Sunken eyes
- Very dry mouth and skin that stays tented when gently pinched
- Inability to keep fluids down
These call for prompt medical attention. Confusion, fainting or severe weakness should be treated as urgent.
Signs in babies and young children
Children can become dehydrated more quickly than adults, especially with stomach illness or fever. Possible signs include fewer wet diapers than usual, no tears when crying, a dry mouth, sunken soft spot on a baby’s head, unusual drowsiness or fussiness, and cool or blotchy hands and feet. Contact a pediatrician or seek urgent care promptly if you notice these, since children should be assessed by a professional.
Older adults
Older adults may show less obvious signs. Confusion, falls, constipation or lowered appetite can sometimes be linked with low fluid intake. Some medicines, such as certain blood pressure treatments and diuretics, can also affect fluid balance. Anyone helping an older relative, perhaps in the context of caring for parents, can encourage regular sips throughout the day and check in with the person’s doctor about any medicines.
What to do for mild dehydration
For a healthy adult with mild symptoms, common-sense steps include:
- Drink fluids gradually. Small, frequent sips are often easier to tolerate than gulping a large amount at once.
- Move somewhere cool and rest if heat or activity was the cause.
- Include foods with plenty of water, such as soup or fruit, if you feel up to eating. Our look at hydrating foods has ideas.
- Pay attention to how you feel over the next few hours.
After vomiting or diarrhea, an oral rehydration solution sold in pharmacies is often recommended by health services because it contains a balance of water, salts and sugar. Ask a pharmacist or doctor about what is suitable, particularly for children or older adults, and follow package directions.
It is best to avoid trying to fix things quickly by drinking a huge amount of plain water, and alcohol is generally not helpful. Heavy coffee or energy drinks are not a good solution either.
Heat-related warning signs
In hot conditions, dehydration can accompany heat exhaustion, which may involve heavy sweating, nausea, headache, weakness and a fast pulse. If someone has a very high body temperature, hot dry skin, confusion or collapses, it may be heatstroke, which is an emergency. Call emergency services and move them somewhere cool while waiting. For more everyday precautions, see hot weather safety.
When to contact a doctor
Seek medical advice if:
- Symptoms do not improve after drinking fluids
- You cannot keep fluids down, or vomiting or diarrhea lasts more than a day or two
- You have a fever with signs of low fluid
- You have diabetes, kidney or heart disease, or take medicines that affect fluids, and become unwell
- A baby, young child or older person shows any signs of dehydration
- You notice very little urine, confusion or fainting
If you are unsure, it is reasonable to call a nurse advice line or your doctor. For a routine appointment about persistent thirst or other changes, it can help to prepare before a doctor visit by noting when symptoms happen and what you usually drink.
Preventing it
Most everyday dehydration is avoidable with a few habits: drinking regularly, extra fluids during heat, illness or activity, and noticing the early signs. You can read more about general drinking water habits and daily hydration without needing to count every glass.