Britain faces its first heatwave of the year before summer officially begins, with temperatures set to climb as high as 33°C in parts of southern England and the Midlands on the bank holiday Monday. The three-day hot spell – meeting the official definition of a heatwave – has prompted yellow and amber heat health alerts across much of England, warning healthcare providers and the public that the sudden warmth poses serious health risks because the body has not yet had a chance to acclimatise.
Forecast and Alerts
The UK is forecast to experience its hottest May bank holiday weekend on record, according to the Met Office. A heatwave is officially recorded when an area records at least three consecutive days with temperatures equal to or above a regional threshold, which varies from 25°C in northern areas to 28°C in the warmer south-east. Much of the country is expected to meet that criteria, with the south and Midlands seeing the highest readings. Heat health alerts have been issued – yellow from Friday morning and amber for parts of England, indicating a heightened risk to health.
The sudden arrival of high temperatures after a long run of unseasonably cool and dull weather in May makes this early-season heatwave particularly dangerous. People are not used to the heat, and the body has not had time to adapt. “Over the past few weeks it’s been quite cool. So people are not acclimatised to these very warm temperatures yet,” said Dr Ross Hemingway, a sports and exercise medicine GP.
How the Body Acclimatises to Heat – and the Risks When It Doesn’t
The human body has two main cooling mechanisms: increasing blood flow to the skin to radiate heat away, and sweating, where heat is lost through evaporation. When the weather stays warm for days or weeks, these processes become more efficient – a process called acclimatisation. But a sudden heatwave, like the one arriving this weekend, means that adaptation has not occurred. As a result, the body is far more vulnerable to overheating and dehydration.
Heat illness occurs when core body temperature rises by 1°C or 2°C above the normal 37.5°C. The risk is significantly higher during physical activity. Dr Hemingway advised people to “dial back initially on how hard they’re pushing themselves” and to exercise before 8am or after 8pm on very hot days. Adequate fluid intake is crucial: drink enough so that you never feel thirsty, before, during and after exercise.
Dehydration can set in within hours, especially if fluid loss is not replaced quickly. Symptoms include fatigue, dizziness, headaches and dry mouth. If left unchecked, heat exhaustion can develop, bringing tiredness, weakness, muscle cramps, nausea and intense thirst. Heatstroke – a life-threatening emergency – is marked by hot, red, dry skin, confusion and loss of consciousness.
Electric fans can help cool indoor spaces, but only when the temperature is below 35°C; above that, fans may not prevent heat-related illness and can increase dehydration. They should not be aimed directly at the body, and hydration must be maintained.
The sun itself also carries immediate risks. Sunburn raises the risk of skin cancer, and the recent lack of sunshine could make people more likely to burn this weekend. “We don’t want people to get caught off guard by a stronger sun,” said Dr Rachel Orritt, health information manager at Cancer Research UK. The National Institute for Health and Care Excellence (Nice) – the NHS medical evidence body – acknowledges that “some sunlight is good for health” because it triggers vitamin D production, essential for strong bones and a healthy immune system. However, Nice advises people to judge from their skin tone how much sun they can take without burning: those with darker skin have a lower risk of burning, while very fair skin can burn in minutes. The latest guidance recommends seeking shade between 11am and 3pm, covering up with clothing and a wide-brimmed hat, and using sunscreen with at least SPF 30 and four or five stars, applied liberally and reapplied regularly.
Persistent high temperatures and sweating can also worsen skin conditions. Dr Babak Ashrafi, a GP for Superdrug, advised wearing loose clothing and showering more often. Hives – an itchy, raised rash – can appear in susceptible people. Chafing, where skin rubs against clothing or other skin, is worsened by heat and moisture; the British Association of Dermatologists recommends keeping the skin dry with talc or using petroleum jelly as a barrier.
Vulnerable Groups: The Toll on Older People and Others
Dehydration becomes increasingly dangerous the longer it persists. Over several days it can lead to blood becoming slightly less watery, which worsens multiple medical conditions. This is one reason heatwaves can be deadly, especially for older people. Five heatwaves between June and August last year – the warmest summer on record – led to more than 1,500 “heat-associated deaths” in England, according to government data. These are not all deaths directly from overheating; rather, they represent a rise in the usual number of daily deaths from heart attacks, strokes, cancer and lung conditions, mainly among people over 75.
The British Geriatrics Society has highlighted that older people living alone or with cognitive impairment are particularly vulnerable. Blood pressure medicines, including ACE inhibitors, angiotensin receptor blockers (ARBs) and diuretics, can interfere with thirst perception and fluid balance, worsening dehydration. Diabetes medications and laxatives can also contribute. The society urges relatives and friends to check in on older people and help ensure they are drinking enough and staying cool.
Beyond the elderly, other groups at heightened risk include infants and young children, people with chronic illnesses such as heart or lung conditions, diabetes, kidney disease or Parkinson’s, those on multiple medications, the homeless, the bed-bound, individuals with drug or alcohol addictions, and people who work or spend significant time outdoors. In care homes and hospitals, mortality during heatwaves has been shown to rise above baseline levels.
Although the 2025 summer saw an estimated 1,504 heat-associated deaths – significantly fewer than the 3,039 originally modelled, thanks to various resilience efforts – the toll remains substantial. The 2022 summer, which included the highest UK temperature ever recorded (40.3°C), saw nearly 3,000 heat-associated deaths. Early-season heatwaves, like the one arriving this weekend, are especially dangerous because people have not yet built up a physiological tolerance and may not have put protective measures in place.
Simple cooling strategies – closing windows during the day and opening them at night, taking cool showers, eating water-rich foods – can help. Water is the best drink; sugary drinks and excessive alcohol should be avoided. Thirst is not always a reliable guide, particularly in older adults; checking the colour of urine – pale or straw-coloured indicates adequate hydration – can be a useful indicator.
The British Geriatrics Society asks that relatives and friends check in on older people living alone or with cognitive impairment, helping to make sure they are drinking enough and staying cool.