Can heat exhaustion cause dehydration?

Heat exhaustion develops when the body struggles to cool itself, often after exertion or prolonged exposure to heat. Sweating is one of the body’s main cooling methods, but ongoing sweating reduces circulating fluid. Dehydration can then make cooling harder, creating a cycle of weakness, headache, dizziness, thirst, nausea and muscle cramps. A person may have heat exhaustion without noticing thirst, especially during activity or when they are already unwell. Learn more about [Dehydration](/conditions/dehydration/) and [Heat Exhaustion](/conditions/heat-exhaustion/).

Move to a cool, shaded or air-conditioned place and loosen extra clothing. Rest, cool the skin with wet cloths or a fan, and take small, frequent sips of water or an oral rehydration drink if the person is awake and able to swallow. Avoid alcohol and strenuous activity while recovering. If vomiting prevents drinking, or symptoms do not start improving after cooling and fluids, arrange prompt medical advice.

Call emergency services if there is confusion, fainting, a seizure, inability to drink, severe weakness, or very hot skin with worsening symptoms. These signs can indicate heat stroke or another serious problem. Do not force fluids into someone who is drowsy, confused or unable to swallow; cool them while waiting for help.

Ask whether your symptoms fit heat exhaustion or dehydration, how much fluid is appropriate for you, and whether medicines or a health condition could increase fluid loss. Mention how long you were in the heat, how much you drank, whether you vomited, and any faintness or change in alertness.