Dr Sarah Jarvis, MBE
Author: Dr Sarah Jarvis, MBE, General Practitioner (GP)

Dr Sarah Jarvis is the Clinical Director of the Patient Platform, an active medical writer, broadcaster, and the resident doctor for BBC Radio 2.

7 min read

Whether it’s the unprecedented heat we’ve seen during the UK’s 2022 heatwave or the regular climate of countries closer to the equator, heat can affect your health. Of course, anyone can get heat exhaustion or heat stroke. But certain groups are at higher risk, particularly if they have underlying health problems, and hot weather can also cause flare-ups of some medical conditions.

Breathe easy – or not

Some estimates suggest more than 1 in 8 people in the population have been diagnosed with asthma at some point. Asthma is more common in children than adults, and in some cases, children grow out of having symptoms. Even so, at least 5.4 million people in the UK currently live with asthma, and about 1 million have ‘severe asthma’, with daily (or almost daily) symptoms and a huge impact on their quality of life, despite treatment.

COPD is another common lung condition, where the flow of air to the lungs is restricted. It’s mostly (but not always) due to smoking and largely affects people in later life. It’s estimated that 3 million people in the UK have COPD, although not all of them have been diagnosed.

Whether you have asthma or COPD, hot weather can make your symptoms worse. There are several reasons:

  • Levels of pollen, which can worsen breathing, tend to be higher.
  • Breathing in hot air can lead to narrowing of the airways.
  • Air pollution is often higher in summer, especially on hot, still days or in cities. In addition, the wildfires seen more often across the world in recent years can greatly increase air pollution.
  • Thunderstorms, which are often preceded by close, humid air, can trigger an increase in levels of small pollen particles which can irritate the smaller airways of the lungs.

If you’re on treatment for a lung condition (usually including inhalers) be sure to take your medication really regularly during hot weather. Be aware of the warning signs that your condition is getting worse and seek medical help early.

Gut stuff

We all know that if you have a tummy bug, with its accompanying diarrhoea and vomiting, you need to replace the fluid you lose. That’s because dehydration can lead to all sorts of short-term symptoms (dizziness, headaches, poor concentration, etc) as well as the risk of acute kidney damage.

But if you have an inflammatory bowel condition such as Crohn’s disease or ulcerative colitis, any flare-up can lead to worsening diarrhoea.

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Sweaty business

Our bodies function best when the temperature and other conditions inside us are extremely tightly controlled. One of the main ways we regulate our body temperature is to sweat. That means anything that affects our body’s normal sweating mechanisms can cause issues.

Some medications for conditions such as depression, Alzheimer’s and other forms of dementia, as well as strong opioid painkillers, can lead you to sweat more. This makes you more prone to dehydration, which in turn leaves you more vulnerable to heat exhaustion and heatstroke, as well as kidney damage.

By contrast, other medications can prevent you from sweating. This too can leave you prone to heatstroke, because you can’t cool your body down effectively. These include:

  • Anticholinergic drugs are used for overactive bladder, Parkinson’s disease, abnormal health rhythms, and more.
  • Carbonic anhydrase inhibitors are prescribed for altitude sickness, heart failure, and epilepsy, among other conditions.
  • Tricyclic antidepressant medicines are sometimes used to treat depression but are also commonly prescribed for nerve pain such as trigeminal neuralgia.

Nervous system concerns

People with multiple sclerosis, which affects many parts of your nervous system, can experience pain, weakness, muscle spasms, issues with their eyesight, and much more. They often find that their balance, eyesight, and tiredness worsen in hot weather – and painful muscle spasms can be particularly hard to cope with. If you have multiple sclerosis, it’s little consolation to know that there’s a name – Uhtoff’s phenomenon – for why even a small increase in body temperature can aggravate symptoms.

Many of the 6 million migraine sufferers in the UK can confirm that along with irregular meals, lack of sleep, bright lights, alcohol, stress, and anxiety, dehydration can trigger the pounding headache (and often nausea, exhaustion, light sensitivity, and more) of migraine.

Postural tachycardia syndrome, or PoTS, is an abnormal response of part of your nervous system – the autonomic nervous system. Common symptoms include light-headedness, fainting, headaches, sweating, poor sleep, palpitations, and chest pain. The cause is an abnormal increase in heart rate, which almost always comes on when you’re in the upright position and improves if you lie down.

Although PoTS is still poorly understood, even today, we know it’s seen more often in people with other medical conditions such as ME/Chronic Fatigue Syndrome and autoimmune conditions such as Lupus and Sjögren’s syndrome. People with PoTS often have problems with sweating in hot weather. This can trigger worsening of palpitations, dizziness, and dehydration.

There are multiple Ehlers-Danlos syndromes (EDS) that can affect the stretchiness and strength of supporting tissues in the body, including skin, joints, blood vessels, and internal organs. Many people with EDS are more prone to headaches and migraines, dizziness, palpitations, and heat rash – all of which can become more problematic in hot weather.


Autoimmune conditions are caused when your immune system, which usually helps you fight off invaders such as bacteria and viruses, recognises part of your immune system as an invader and attacks it. Autoimmune conditions like Lupus and rheumatoid arthritis cause joint pain and fatigue. UV rays from direct sunlight can cause flare-ups of both these conditions.

If you have either of these conditions, you should avoid direct sunlight whenever you can. If you are outdoors, protect your skin with long sleeves, trousers, a broad-brimmed hat, and high-factor sunscreen.

Other conditions

The skin condition rosacea affects the skin of your face, leading to flushing, redness, acne-like spots, and thickening of the skin. It affects as many as 1 in 10 people in the UK and the sun can irritate rosacea, worsening flushing and redness.

And spare a thought for people who are visually impaired: sunglasses can affect light perception; and if they use echolocation, it’s more difficult if they have to wear a wide-brimmed hat.

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