U.K. — The UK Health Security Agency (UKHSA) issued public health guidance regarding precautions during hot weather to help reduce the risk of heat exhaustion and heatstroke. The body's core temperature is typically around 37C, and as temperatures rise, the body attempts to lose heat by opening blood vessels near the skin and initiating sweating.

Opening blood vessels lowers blood pressure, requiring the heart to work harder to circulate blood. This process can lead to symptoms such as an itchy heat rash or swollen feet. Sweating causes the body to lose fluids and salt, which can alter their balance. The combination of lowered blood pressure and losses of fluid and salt can result in heat exhaustion.

Symptoms of heat exhaustion include dizziness, nausea, fainting, confusion, muscle cramps, headaches, heavy sweating, and tiredness. If blood pressure drops too far, the risk of heart attacks rises. Most heat-related excess deaths are due to heart attacks and strokes caused by the strain of trying to keep body temperatures stable.

If a person does not recover from heat exhaustion within 30 minutes, they are at risk of heatstroke, which is a medical emergency requiring immediate attention. Individuals experiencing heatstroke may have a temperature exceeding 40C, stop sweating despite being overheated, or experience seizures and loss of consciousness. The higher death rate from heat starts to increase once the temperature passes 25C-26C. Evidence suggests heat-related deaths tend to be caused by higher temperatures in spring or early summer, and previous heatwaves indicate the increase in deaths happens within the first 24 hours.

The UKHSA advises individuals to keep out of the sun between 11:00 and 15:00, seek shade, use sunscreen with a high SPF and UVA rating, and wear a wide-brimmed hat. Avoiding physical exercise during the hottest part of the day and carrying water when traveling are also recommended. The agency also suggests staying cool indoors by closing curtains on sun-facing rooms, drinking plenty of fluids, and limiting alcohol consumption.

Certain groups face a greater risk of serious harm from hot weather, including older people, babies, and young children. The UKHSA recommends checking on older individuals, those with underlying health conditions, and those who live alone. People with long-term conditions like heart disease may struggle more with the strain heat places on the body. Diabetes can lead to faster water loss and alter blood vessels or the ability to sweat. Children and less mobile individuals may also be more vulnerable.

Brain diseases such as dementia can diminish awareness of heat or the ability to respond to it. Individuals experiencing homelessness are also more exposed to the sun, and those residing in top-floor flats may encounter higher indoor temperatures. No one, especially babies, young children, and animals, should be left in a locked vehicle.

The NHS advises moving a person with suspected heat exhaustion to a cool place, having them lie down, and slightly raising their feet. They should drink water, sports drinks, or rehydration drinks. Cooling the skin with cool water, fanning, or using cold packs on areas like the armpits or neck can also help. The NHS states that people should continue taking their medication as usual during hot weather.

Some medications can interact with heat. Diuretics increase water expulsion, potentially leading to dehydration and mineral imbalances in high temperatures. Antihypertensives, which lower blood pressure, can combine with dilating blood vessels to cause sharp drops in blood pressure during warm conditions. Drugs for epilepsy and Parkinson's can inhibit sweating, hindering the body's natural cooling process. Additionally, medications like lithium or statins can become more concentrated and problematic in the blood if too much fluid loss occurs.

In 2022, England reached its highest recorded temperature of 40.3C, resulting in an estimated 2,985 excess deaths due to heat. There were an estimated 1,311 heat-associated deaths in England during summer 2024 and 1,504 heat-associated deaths in England during summer 2025.