What are the risk factors for dehydration?

Dehydration occurs when the body loses more fluid than it replaces. [Gastroenteritis](/conditions/gastroenteritis/) can cause vomiting and diarrhoea, while fever and poor appetite may reduce drinking. Hot, humid conditions, exercise, outdoor work and [Heat Exhaustion](/conditions/heat-exhaustion/) increase losses through sweat. Babies, older adults and people who depend on others for drinks may become dehydrated more easily. Diabetes, kidney problems and medicines that increase urination can also alter fluid balance.

Drink regularly, with extra fluids during heat, exercise or illness. Take small, frequent sips if nausea makes drinking difficult. During significant vomiting or diarrhoea, ask a pharmacist or clinician about an oral rehydration solution rather than relying only on plain water. Keep vulnerable family members within reach of drinks and check on them in hot weather. If you have heart or kidney disease, ask how much fluid is suitable before increasing intake substantially.

Seek urgent medical care for confusion, fainting, severe weakness, inability to keep fluids down, very little or dark urine, rapid breathing, or worsening dizziness. Emergency help is needed if someone is difficult to wake, has a seizure, or collapses. Children, older adults and people with serious long-term conditions may need assessment sooner because they can deteriorate quickly. Read more about [Dehydration](/conditions/dehydration/).

How much should I drink during illness or hot weather? Do my medicines increase fluid loss? Should I use oral rehydration solution? Which symptoms mean I need urgent assessment?