Causes of Dehydration

Dehydration is simple arithmetic: more water and salts leaving the body than coming in. The causes sort into three everyday buckets - losing too much, taking in too little, or both at once.

Losing too much fluid

• Diarrhoea and vomiting: the biggest cause worldwide, and the most dangerous in children - a small body can lose its reserves in a day
• Fever: every degree of temperature raises fluid loss through faster breathing and sweating
• Sweating: Indian summers, heatwaves, hard outdoor work, sports - sweat takes salts with it, not just water
• Excess urination: uncontrolled diabetes (high sugar drags water out), diuretic medicines, and alcohol

Taking in too little

• Simply not drinking enough: busy days, travel, avoiding water to avoid public toilets
• Illness with poor appetite or a sore throat that makes swallowing hurt
• Infants dependent on others for fluids, and elderly people whose thirst signal fades with age

The dangerous combinations

• Vomiting plus diarrhoea together (gastroenteritis, food poisoning, cholera)
• Fever plus summer heat
• Fasting in hot weather
• Hard exercise in the afternoon sun without replacing fluids

Who runs out fastest

• Infants and young children: small reserves, fast losses - the group doctors worry about most
• The elderly: blunted thirst, often on diuretics, slower to notice
• Outdoor workers and athletes in hot months
• People with diabetes, kidney disease, or on water tablets

One-line summary

Dehydration comes from diarrhoea and vomiting, fever, sweating, or simply not drinking - with infants, the elderly, and anyone losing fluids in the heat running out of reserves fastest.