What happens if dehydration is not treated?

Dehydration occurs when the body loses more fluid than it replaces, through vomiting, diarrhoea, fever, sweating, or difficulty drinking. Early clues can include excessive thirst, dark urine, dry mouth, constipation, headache, or dizziness. As fluid levels fall, blood pressure may drop and the heart may work harder to circulate blood. Severe dehydration can cause confusion, fainting, kidney injury, or loss of consciousness. Infants, older adults, and people who are unwell may deteriorate faster.

Take frequent small sips of water or an oral rehydration drink if you can swallow and keep fluids down. If vomiting or diarrhoea continues, ask a clinician or pharmacist which rehydration product is suitable. Keep track of urination and alertness. Do not rely on thirst alone, and do not delay advice when a child, older person, or person with a long-term illness cannot replace lost fluids.

Seek urgent help for fainting, confusion, extreme sleepiness, very little or no urine, rapid breathing, severe weakness, or inability to keep fluids down. Medical assessment is also needed when dehydration follows heavy bleeding, severe diarrhoea, or persistent vomiting.

Ask what may be causing the fluid loss, how much and what type of fluid is appropriate, and whether medicines or illness increase your risk. Ask which changes in urination or alertness should prompt urgent care.