According to the Met Office, a heatwave is declared when a location records a period of at least three consecutive days when daily maximum temperatures meet or exceed the heatwave temperature threshold for that area.
Most counties in the south east of England, for example, have a threshold of 27C, while central areas of England and the south-east of Wales have a threshold of 26C.
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Controversially, the Met Office raised the threshold for eight counties in England last year by 1C, making the threshold for declaring a heatwave higher.
There is no exact measure for when heat becomes dangerous to human health, as certain people are more vulnerable to heat than others due to pre-existing conditions or difficulty regulating their body temperature.
The elderly, the disabled and people with long-term health issues are more susceptible to death or heat stroke when higher temperatures hit, for instance. This is why knowing how to cool down at home is crucial whenever temperatures rise.
However, when heat combines with humidity it can create what’s known as “wet bulb temperature” – the lowest temperature to which an object can cool down when moisture evaporates from it.
Wet bulb temperature measures how well our bodies are able to cool down by sweating when it’s hot, and the lower the wet bulb temperature, the easier it is for us to cool ourselves down.
If wet bulb temperature reaches the same level as the temperature of our skin, it becomes impossible for us to cool ourselves down by releasing heat from our bodies or sweating, and the impact can be deadly.
Scientists estimate a prolonged wet bulb temperature of above 35C can be deadly even for the healthiest people.
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How can I cool down in the day?
If you’re at home during the day, whether working or relaxing, knowing how to cool down will prevent you from feeling uncomfortable or getting unwell. Easy actions you can take include:
- Closing curtains or blinds in rooms facing the sun
- Drinking plenty of water throughout the day
- Wearing loose clothing made of thin, breathable fabrics
- If the temperature outside is cooler than inside, opening some windows
- Using air conditioning or fans to keep yourself cool
- Keeping lights and other appliances off
- Using a wet flannel on the back of your neck
- Taking a lukewarm shower – and being careful not to opt for freezing cold water, as your body will try to heat up again quickly afterwards
How can I cool down at night?
As well as taking the above measures, knowing how to cool down at night is key to getting a proper night’s sleep. Actions you can take include:
- Moving to a cooler room where possible. If your home has two levels, opt for the downstairs level as heat tends to rise
- Sleeping with a fan on can help cool you down, but it can also aggravate allergies, so this is something to be aware of
- Wearing thin clothing to bed and opting for lightweight cotton bedclothes
- Cooling your socks or your bedclothes in the fridge before bed – cooling down your feet can have a particularly effective impact on your body temperature
- Tying your hair up if it’s long to keep it off your face
- Avoiding sharing a bed if possible
- Avoiding big meals or exercise before bedtime
How can I make my house cooler generally?
Longer term, there are ways that homeowners can make their living space more resilient to high temperatures. If you’re able to, you could consider:
- Using pale and reflective paint on the outside of your home, and pale paint indoors too
- Having your loft and cavity walls insulated
- Growing leafy plants and trees near windows to act as air conditioners
- Installing stutters on your windows to keep the sun out
If you live in a rented home, your landlord has a responsibility to make sure that the conditions in it are liveable, so you should contact them as a first port of call if your home is uncomfortably hot.
If the landlord doesn’t act, you could ask your local council to perform a “health and safety standards for rented homes” assessment.
This will assess hazards in your home which could affect your health and could lead to the council forcing your landlord to take action.
If you rent from the council and are not satisfied with their response to overheating in your home, you could consider complaining to the housing ombudsman here.
What are the symptoms of heat stroke?
Too much exposure to heat can lead to heat exhaustion or heat stroke. Symptoms include:
- Dizziness and confusion
- A headache
- Feeling sick and/or loss of appetite
- Excessive sweating and clammy skin
- Being very thirsty
- Cramps in the legs, arms and stomach
Children with heat stroke may also become floppy and tired. To help someone recover from heat stroke, they must be cooled down quickly. You can help by doing the following:
- Moving the person to a cool place or room
- Getting them to drink lots of water
- Getting them to lie down and raise their feet slightly
- Cooling their skin down by, for instance, giving them a cold flannel