Dehydration

Dehydration happens when the body loses more fluid than it takes in, affecting normal function.

Water helps control temperature, circulate blood and remove waste. Losing fluid through heat, sweating, vomiting, diarrhoea, fever or frequent urination can reduce the fluid available for these jobs. It can develop gradually when drinking does not keep pace with losses, or more quickly during an acute illness.

Thirst, a dry mouth, reduced urination and urine that looks darker than usual can occur. Headache, dizziness, tiredness, general weakness and muscle cramps are also common presentations of dehydration. Some people become light-headed on standing because their circulation has less fluid to work with.

Confusion, fainting, inability to keep fluids down, marked drowsiness or very little urine need urgent medical assessment. In babies and young children, fewer wet nappies, unusual sleepiness, no tears when crying, or a sunken soft spot on the head also deserve prompt attention.

Hot weather, strenuous activity and not having drinks readily available can lead to losses that are not replaced. Vomiting and diarrhoea can remove both water and salts. Fever increases fluid needs, while some medicines, including water tablets, may increase urination. High blood sugar and kidney problems can also be relevant, so repeated dehydration merits a clinical review.

Older adults may not feel thirst as strongly or may need help reaching drinks. Infants and young children have smaller fluid reserves and can deteriorate during vomiting or diarrhoea. People working outdoors, exercising in heat, living with swallowing difficulties, or recovering from illness may need a planned approach to fluids.

A clinician will ask about recent fluid intake, heat exposure, illness, urine output and medicines. They may check pulse, blood pressure, temperature, mouth moisture and alertness. Urine or blood tests can help identify dehydration, changes in salts, infection or another cause when symptoms are significant or ongoing.

Mild dehydration can often be managed with frequent small sips of fluid. An oral rehydration drink may be useful when vomiting or diarrhoea has caused salt losses; prepare it exactly as directed. Continue usual food when it is tolerated, unless a clinician has advised otherwise. Avoid relying on very sugary drinks or alcohol to rehydrate.

If someone cannot drink enough, is repeatedly vomiting, has severe symptoms, or has a condition that affects fluid balance, medical care may be needed. Intravenous fluids are used in clinical settings when oral replacement is unsuitable or insufficient.

Drink regularly through hot days and take fluids before, during and after activity. Carry water when travel or work limits access to drinks. During a stomach illness, begin small frequent sips early and watch urine output. People with fluid restrictions from heart, liver or kidney disease should follow their own clinician's advice rather than increasing fluids without guidance.

Arrange a GP appointment for recurring dehydration, ongoing thirst, recurrent vomiting or diarrhoea, or symptoms that do not improve with drinking. Seek urgent help for fainting, confusion, severe weakness, chest pain, trouble breathing, or a child who is difficult to wake. Assessment can address both the fluid loss and the reason it occurred.