Symptoms of Dehydration and Heat Exhaustion

Dehydration develops when the body loses more fluid than it replaces. Heat exhaustion can occur after exposure to heat, especially with sweating and physical activity, and dehydration can make it harder for the body to cool itself. The two can happen together.

Early dehydration may cause excessive thirst, a dry mouth, tiredness, less frequent urination, or urine that looks darker than usual. You may also notice a headache or dizziness, particularly when standing or walking.

Heat exhaustion often causes heavy sweating, clammy skin, weakness, headache, dizziness, nausea, muscle cramps, or difficulty concentrating after being in a hot environment. Sweating can remain heavy because the body is trying to release heat. Symptoms can worsen during exercise, outdoor work, or time in a hot, poorly ventilated place.

Symptoms overlap with other problems, so they do not identify one cause on their own. Heat intolerance, vomiting, diarrhoea, fever, medicines, and illnesses can also affect fluid balance or temperature control.

Stop physical activity and move to a cool or shaded place. Loosen extra clothing, use cool wet cloths or a fan, and rest. Sip water slowly; an oral rehydration drink may be useful when fluid loss has followed heavy sweating, vomiting, or diarrhoea.

Avoid alcohol and further exertion while recovering. Do not force large amounts of fluid at once, and do not give anything by mouth to a person who is confused, faint, or unable to swallow safely. If symptoms do not begin to improve with cooling and fluids, arrange medical assessment.

Call emergency services for confusion, loss of consciousness, a seizure, trouble breathing, severe weakness, or very hot skin with a change in behaviour. These signs can indicate a dangerous heat-related illness rather than uncomplicated heat exhaustion.

Seek prompt medical advice for persistent vomiting, inability to drink, worsening dizziness, very little urine, severe headache, chest pain, or symptoms that continue after cooling and rest. Be especially cautious with a child, older adult, pregnant person, or anyone with a chronic illness or taking medicines that affect fluid balance.

Ask what may have triggered the symptoms, whether you need an examination or blood tests, and which fluids are suitable for you. Mention the heat exposure, activity, fluid intake, urination, vomiting or diarrhoea, and all medicines or supplements you use.