Vomiting and diarrhoea make you lose fluids and salts quickly, which can lead to dehydration if not replaced. Early signs include thirst, a dry mouth and lips, passing less urine that is darker than usual, feeling tired, light-headed or having a headache. Children may have fewer wet nappies, be unusually sleepy or irritable, and lack tears when crying.
To prevent and treat mild dehydration, sip fluids regularly and use oral rehydration salts, which replace water and essential salts. Take small frequent sips if you feel sick. Avoid large amounts of sugary or caffeinated drinks.
Seek urgent care or call your local emergency number for signs of severe dehydration: confusion or drowsiness, fainting, a rapid heartbeat, sunken eyes, very little or no urine for many hours, or inability to keep any fluids down. Babies, older adults and people with chronic illness can deteriorate quickly and should be assessed early.