What should you know about mild, moderate and severe dehydration?

Dehydration happens when the body loses more fluid than it replaces. Early clues include thirst, a dry mouth, headache, tiredness, and urine that is darker or less frequent than usual. As fluid loss continues, standing may make you light-headed, your heartbeat may feel faster, and you may become unusually weak. Severe dehydration can affect alertness, circulation, and the ability to keep fluids down. Vomiting, diarrhoea, fever, heavy sweating, hot conditions, and not drinking enough can all contribute. Dark urine can have other causes, so one symptom alone does not establish dehydration.

If you are alert and able to swallow, take frequent small sips of water. After vomiting or diarrhoea, an oral rehydration solution can replace water and salts; follow the product directions. Rest somewhere cool, pause strenuous activity, and avoid alcohol. If nausea makes drinking difficult, try a sip at a time rather than a large glass. Babies, older adults, people who are pregnant, and anyone with kidney or heart problems may need individual advice. A clinician can assess the cause, hydration status, and whether treatment such as supervised fluids is needed.

Seek urgent medical help for confusion, fainting, severe weakness, very little or no urine, rapid breathing, cold or clammy skin, or an inability to drink or keep fluids down. Get prompt advice when dehydration follows persistent vomiting, diarrhoea, heat exposure, or a medical condition. If symptoms are mild but do not improve after replacing fluids, arrange a GP consultation. Severe symptoms can require emergency treatment, especially in a child or frail adult.

Ask what may be causing the fluid loss, which drinks or oral rehydration product suit you, how to monitor urine and alertness, and whether your medicines need review during illness.