Dehydration and temperature: what to know

Your body uses fluid for sweating and blood circulation, both of which help release heat. When you lose more fluid than you take in, sweating may reduce and your body may feel unusually hot. A raised temperature can also occur with an illness that is causing fluid loss, such as vomiting or diarrhoea, so dehydration and fever can happen together without one fully explaining the other.

Heat exposure, strenuous activity and gastroenteritis can all increase fluid loss. Chills, weakness, headache, thirst, a dry mouth or dark urine add useful context, but temperature alone cannot show how dehydrated you are.

Move to a cool place, loosen extra clothing and rest. Take frequent small sips of water; an oral rehydration drink may help when vomiting or diarrhoea has caused losses of fluid and salts. Avoid alcohol, and do not rely on very sugary drinks as your main rehydration choice. Check whether you are passing urine and whether its colour becomes lighter as you recover.

Get urgent medical help for confusion, fainting, a seizure, severe weakness, trouble breathing, inability to keep fluids down, or very little or no urine. A very high temperature after heat exposure, hot dry skin, or worsening symptoms can signal a heat emergency. Contact a clinician if fever persists, fluid loss continues, or you have kidney disease, heart failure, diabetes, are pregnant, or are caring for a young child or older adult.

Ask whether your temperature is more consistent with infection or heat illness, which rehydration drink is suitable for you, and whether any medicines or medical conditions change how much fluid you should take.