Symptoms of sunstroke and dehydration

Dehydration occurs when the body loses more fluid than it replaces. Heat, sweating, vomiting, diarrhoea, fever, or not drinking enough can contribute. Dark urine, constipation, headache, tiredness and muscle cramps may accompany fluid loss; urine colour can also change for other reasons.

Heat exhaustion may cause heavy sweating, clammy skin, nausea, weakness and light-headedness. Sunstroke or heat stroke is more severe: confusion, collapse, seizure, or very hot skin indicates that the brain and body are being affected and needs emergency help.

Move to a cool place, rest, loosen tight clothing, and take frequent small sips of water or an oral rehydration drink if you are alert and can swallow. After vomiting or diarrhoea, an oral rehydration solution may replace salts as well as fluid. Avoid alcohol and strenuous activity while recovering.

Do not force drinks on someone who is confused, very sleepy, or vomiting repeatedly. A clinician can check whether dehydration relates to gastroenteritis, a urinary infection, or another problem and can advise if you have kidney disease or take fluid-affecting medicines.

Call emergency services for confusion, fainting, seizure, severe overheating, breathing difficulty, or inability to drink safely. Seek prompt medical advice for very little urine, worsening dizziness, persistent vomiting or diarrhoea, blood in urine, or pain suggesting kidney stones or a urinary tract infection. Children, older adults, and people with chronic illness can become unwell quickly.

Ask how much and what type of fluid is suitable, whether your medicines need review during hot weather, and whether changes such as cloudy urine, constipation, or dark urine need testing.