Why hot weather can leave you tired, thirsty, dizzy or unwell and the simple things you can do to help your body cope before the heat becomes a problem
There is a particular kind of tiredness that can creep in on a very hot day.
You have not necessarily done anything strenuous. Maybe you have only walked to the shops, sat on a bus without air conditioning or spent the afternoon working in a room that refuses to cool down.
Yet suddenly, you feel drained.
Your head feels heavy. Your mouth is dry. You are irritable for no obvious reason, and standing up too quickly makes the room shift slightly beneath you.
That is not simply you being “bad with heat”.
Your body is working harder than you might realise.
When the temperature around you rises, your body has to continuously regulate its own internal temperature. It does this largely by increasing blood flow towards the skin and producing sweat. As sweat evaporates, it removes heat from the skin and helps cool you down. (UK Health Security Agency Blog)
Most of the time, that system works beautifully.
But there is a limit.
When temperatures stay high, particularly when humidity is also high, your body may struggle to lose heat efficiently. Add dehydration, strenuous exercise, illness or certain medications into the mix, and what began as “just a hot day” can become a genuine health problem.
What actually happens to your body when you get hot?
Your body likes stability.
Even while the weather around you changes dramatically, it works to keep your internal temperature within a relatively narrow range.
As you warm up, blood vessels near the surface of your skin widen. This increases blood flow to your skin, allowing more heat to escape.
You also sweat.
Sweating itself is not what cools you. The cooling happens when sweat evaporates from your skin.
That distinction matters.
On a dry day, sweat may evaporate relatively efficiently. In very humid conditions, the surrounding air already contains a great deal of moisture, so evaporation becomes less effective. Your skin may be dripping with sweat while your body is still struggling to cool itself.
The World Health Organisation explains that prolonged exposure to excessive heat can strain the body and worsen existing cardiovascular, respiratory, kidney, and other health conditions. (World Health Organisation)
In other words, heat is not only uncomfortable.
It creates physiological work.
Where does hydration come into it?
Every time you sweat, you lose water.
You also lose electrolytes minerals including sodium that help support normal nerve, muscle and fluid function. (CDC)
Usually, you replace these losses by drinking and eating.
The difficulty starts when your losses outpace what you take in.
That is dehydration.
And it can happen more subtly than people expect.
You do not have to be stranded in a desert or exercising for hours. A hot bedroom, long commute, outdoor job, busy shift, sightseeing trip or afternoon in the sun can be enough to leave you under-hydrated if you are not drinking regularly.
Signs can include:
- thirst
- a dry mouth
- darker urine or urinating less often
- headache
- tiredness
- dizziness
- difficulty concentrating.
The World Health Organisation recommends drinking water regularly during hot weather, rather than relying entirely on thirst to remind you. (World Health Organisation)
But there is no single perfect amount of water that suits everyone in every situation.
How much you need can vary with your body size, activity level, climate, pregnancy, illness, diet, and how much you sweat. People who have been told to restrict fluids because of heart, kidney or other medical conditions should follow their individual healthcare advice rather than suddenly increasing their fluid intake.
Do you really need litres and litres of water?
This is where sensible hydration advice can quickly turn into an online competition.
You may see rules telling you that everyone needs exactly two litres, three litres or even four litres of water every day.
Human bodies are not quite that standardised.
Your fluid needs change.
Someone sitting indoors in mild weather may need much less additional fluid than someone working outdoors in high temperatures.
Rather than forcing down huge amounts all at once, think regularly and consistently.
Keep water within reach. Drink throughout the day. Have something to drink with meals. Take water when you leave the house.
If you are sweating heavily for prolonged periods through exercise or physical work, replacing electrolytes as well as fluid may sometimes be helpful. The CDC notes that heat exhaustion commonly results from excessive loss of water and salt through sweating. (CDC)
For most ordinary day-to-day situations, however, you do not need to turn hydration into a complicated science project.
Water, regular meals and paying attention to how you feel will take you a long way.
When feeling hot becomes heat exhaustion
There is a difference between feeling uncomfortable in the heat and becoming unwell because of it.
Heat exhaustion can develop when your body loses too much water and salt and is struggling with the heat.
According to the NHS, signs can include tiredness, dizziness, headache, nausea or vomiting, excessive sweating, cramps, thirst, weakness and a fast heartbeat or breathing rate. (nhs.uk)
Someone with heat exhaustion needs to cool down.
Move them somewhere cooler, remove unnecessary outer clothing and encourage them to drink cool fluids if they are awake and able to drink safely.
Cooling the skin can also help, for example, with cool water, a damp cloth, a fan or cool packs wrapped in fabric.
And pay attention to what happens next.
If the person is not improving after cooling measures, becomes increasingly confused or develops signs of heatstroke, they need urgent medical attention.
Heatstroke is different, and it is an emergency
Heatstroke is not simply “really bad heat exhaustion”.
It is a medical emergency in which the body’s temperature-control system fails, allowing body temperature to rise dangerously. (CDC)
Warning signs can include:
- confusion or altered behaviour
- poor coordination
- collapse or loss of consciousness
- seizures
- very high body temperature
- hot skin, which may be dry or still sweating
- rapid breathing or a rapid pulse.
One particularly important point: do not wait for someone to stop sweating before taking heatstroke seriously.
Although dry, hot skin can occur, people experiencing heatstroke may still be sweating heavily. (CDC)
If you suspect heatstroke, contact your local emergency medical service immediately and begin cooling the person while help is on its way.
This is not the moment to tell someone to “sleep it off” or wait and see how they feel later.
Who needs to be particularly careful in hot weather?
Heat can affect anyone, but some people are more vulnerable.
Risk can be greater for older adults, babies and young children, people with disabilities, people who live alone, and those living with conditions affecting the heart, lungs, kidneys or other body systems. (World Health Organisation)
Certain medicines can also affect how the body responds to heat or dehydration.
That does not mean you should stop taking prescribed medication when the weather gets hot.
Instead, if you take regular medication and have concerns about heat, hydration or your ability to regulate temperature, speak to a doctor or pharmacist.
And remember that the medicine itself may need protecting from extreme temperatures too.
Can Heat Make Medication Less Effective? What You Need to Know
Small things that make hot days easier on your body
Staying safe in hot weather does not have to involve spending your entire summer indoors beside an air conditioner.
Often, it is about reducing the amount of work your body has to do.
Try to:
- drink regularly throughout the day
- carry water when you are out
- avoid excessive alcohol, particularly during very hot weather
- wear loose, lightweight clothing
- use shade where possible
- move strenuous exercise or outdoor tasks to cooler parts of the day
- take cool showers or baths
- use fans appropriately and keep living spaces as cool as you reasonably can
- close blinds or curtains when strong sunlight is heating your home
- check on people who may find it harder to cope with the heat.
The WHO recommends combining hydration with practical cooling measures such as light clothing, cool showers or baths and reducing exposure to excessive heat. (World Health Organisation)
The idea is not to become frightened of warm weather.
It is to notice when your body is beginning to struggle.
Sometimes your body whispers before it shouts
One of the easiest mistakes to make in hot weather is dismissing early symptoms.
I’m just tired.
I haven’t eaten enough.
It’s only a headache.
I’ll drink something later.
Sometimes those explanations are completely correct.
But during very hot weather, thirst, headache, dizziness, nausea, weakness and unusual fatigue deserve a little more attention.
Your body is remarkably good at keeping itself balanced, but it cannot do everything without your help.
Drink regularly.
Give yourself opportunities to cool down.
Do not push through significant symptoms simply because everybody else seems to be coping.
And keep an eye on the people around you too. The older neighbour who has not opened their windows all day. The child who has suddenly become unusually sleepy. The colleague who looks pale and says they feel dizzy. The friend who insists they are fine despite becoming confused.
Protecting your health during hot weather often begins with noticing the small signs early before they become something bigger.
Because sometimes the most useful health advice really is that simple:
Pay attention.
Cool down.
Have a drink.
And know when “I’m just hot” has become something that needs help.
Medical Disclaimer
This article is for general health information and does not replace personalised advice from a doctor, pharmacist or other qualified healthcare professional. If someone has symptoms of heatstroke or is seriously unwell, contact the appropriate emergency medical service in your area.
