What is the medical term for dehydration?

Your body loses fluid through urine, sweat, breathing, vomiting, and diarrhoea. Dehydration develops when replacement does not keep up with those losses. Thirst, a dry mouth, tiredness, dizziness, headache, and darker urine can occur. Constipation may also appear when less water reaches the bowel; persistent dark urine can be a useful sign to discuss with a clinician.

The cause matters. Gastroenteritis can remove fluid through vomiting or diarrhoea, while heat exhaustion can increase losses through sweating. Dehydration can also make urine more concentrated, but cloudy urine or urinary pain may have another cause.

If you are alert and able to drink, take frequent small sips of water. After vomiting or diarrhoea, an oral rehydration solution can help replace fluid and salts; follow the product directions. Rest somewhere cool if heat or exercise contributed, and avoid alcohol while recovering. Do not force large amounts quickly if that worsens nausea. People with kidney, heart, or other conditions affecting fluid balance should ask a clinician how much to drink.

Get urgent medical help for confusion, fainting, severe weakness, inability to keep fluids down, very little urine, or rapid worsening. Seek prompt advice if dehydration follows prolonged vomiting or diarrhoea, occurs in a young child or older adult, or does not improve after drinking. Fever, severe abdominal or back pain, blood in urine, or painful urination may point to a separate problem such as a urinary tract infection or kidney stones.

Ask what may have caused the fluid loss, whether an oral rehydration solution is suitable, and which symptoms would require same-day assessment. Mention your urine changes, bowel symptoms, medicines, and any kidney or heart condition.