What causes dehydration?

Fluid leaves the body through urine, sweat, breathing and stools. Loss increases with gastroenteritis, heat exhaustion, fever, heavy exercise, or ongoing vomiting and diarrhoea. Pain, nausea, mobility difficulties, swallowing problems and some medicines can make drinking harder. Frequent urination can occur with diabetes or a urinary infection. Dark urine, a dry mouth, thirst, constipation, headache, tiredness and dizziness can accompany fluid loss.

Dehydration can worsen quickly in babies, older adults and people who are pregnant or have a long-term illness. Cloudy urine has several possible causes and does not by itself prove dehydration; the overall pattern and how the person feels matter.

Take small, frequent sips if nausea is present. Oral rehydration solution can replace water and salts lost through vomiting or diarrhoea; prepare it exactly as directed. Continue suitable breast or formula feeds for infants and ask a clinician about children. Water-rich foods may help when tolerated. Avoid relying on alcohol, and seek advice before changing fluid intake if you have kidney or heart disease.

Seek urgent help for confusion, fainting, severe weakness, very little or no urine, fast breathing, inability to keep fluids down, blood in vomit or stool, or severe abdominal pain. Babies with fewer wet nappies, a dry mouth or unusual sleepiness need prompt assessment. Medical review is needed when diarrhoea or vomiting continues, or when heat-related symptoms do not improve after cooling and fluids.

Ask what fluid and rehydration product is suitable, whether medicines may be increasing fluid loss, and whether symptoms such as dark urine, constipation or frequent urination need another explanation.