Hot weather can place sudden strain on the heart, brain and circulatory system. The UK Health Security Agency (UKHSA) says anyone can be affected, but older people, babies, young children and those with long-term conditions need extra care. Simple steps such as staying cool, drinking enough fluids and avoiding the strongest sunlight can prevent heat exhaustion. If symptoms worsen or do not improve, heatstroke can develop and become a medical emergency.
How extreme heat changes the body
The body normally works to maintain a core temperature of about 37°C. When temperatures rise, blood vessels near the skin widen so more heat can be released into the surroundings. This helps cooling, but it can also lower blood pressure and make the heart work harder to circulate blood. The added cardiovascular strain can contribute to heat rash, swollen ankles or feet, and, in vulnerable people, a greater risk of heart problems.
Sweating is the body’s other major cooling system. As sweat evaporates from the skin, it carries heat away. But perspiration removes water and salts, disrupting the delicate balance needed for normal circulation, muscle function and organ activity. When fluid loss becomes significant, especially in a hot environment, heat exhaustion can follow.
Common symptoms include dizziness, nausea, fainting, confusion, muscle cramps, headache, heavy sweating and unusual tiredness. Confusion is particularly important because it may signal that the condition is becoming more serious. Heat can turn quickly, and an initially mild headache or weakness should not be ignored in someone who is older, unwell or unable to cool themselves.
Practical precautions recommended by UKHSA include closing curtains in rooms facing the sun, drinking plenty of fluids, limiting alcohol, staying in the shade and avoiding exercise during the hottest part of the day. People should also seek shade, use sunscreen with a high SPF and UVA rating, wear a wide-brimmed hat and avoid direct sunlight between 11:00 and 15:00, when its rays are strongest. Anyone travelling in hot weather should carry water, while those considering cooling off in a river or open water should check local warnings for hidden hazards.
Who is most vulnerable in hot weather?
Older adults are more likely to struggle because the body may respond more slowly to rising temperatures. Babies and young children heat up faster and depend on others to keep them cool and hydrated. People with reduced mobility may also find it harder to move to a cooler place or obtain fluids.
Long-term health conditions can add to the risk. Heart disease reduces the body’s ability to cope with the extra demand placed on the circulation. Diabetes can cause faster water loss, while some complications can affect blood vessels and the ability to sweat. Dementia and other brain conditions may mean a person does not recognise the heat or knows what to do to protect themselves.
Social and environmental circumstances matter too. Someone who lives alone may have no one to notice early symptoms, while people experiencing homelessness have little protection from prolonged