Heat-related fever: what to know

A raised temperature can occur after prolonged heat exposure, strenuous activity, or an infection that happens at the same time. Heat illness may also cause thirst, weakness, headache, dizziness, nausea, and heavy sweating. Fever itself is a regulated immune response, whereas overheating can raise body temperature because the body cannot release heat effectively. A hot environment does not prove that the temperature is caused by heat, so new cough, sore throat, rash, burning urine, or a local painful area may point toward infection instead.

Move to a cool, shaded or air-conditioned place and loosen extra clothing. Rest, use cool wet cloths, and offer small frequent sips of water if the person is awake and can swallow. Avoid alcohol and strenuous activity. Do not give drinks to someone who is confused, vomiting repeatedly, or unable to swallow. Recheck how they feel after cooling, and arrange medical advice if symptoms continue. A clinician may look for infection as well as dehydration or heat illness; related explanations include [Common Cold](/conditions/common-cold/) and [COVID-19](/conditions/covid-19/).

Call emergency services for confusion, fainting, a seizure, difficulty breathing, collapse, or skin that is very hot with worsening illness. Seek urgent medical assessment when the person cannot keep fluids down, remains unusually weak after cooling, or has a persistent high temperature. Children, older adults, pregnant people, and those with long-term medical conditions can become unwell quickly. Do not delay because sweating is present or absent.

Ask whether the pattern fits heat illness or infection, whether medication could affect temperature control, and which fluids or fever treatments are suitable. Tell the clinician when symptoms began, how long the heat exposure lasted, any measured temperatures, and whether there was vomiting, rash, cough, or urinary discomfort.