Hot weather can make pain worse – here’s why

This summer’s amber heat warnings have brought with them many risks to health.

Many people have experienced these health effects first-hand: brain fog, physical fatigue, restless nights and reduced productivity. If that sounds familiar, you’re not imagining it. Science shows that high temperatures can affect both our bodies and our brains – even before they reach extreme levels.

But one consequence of hot weather that many people may not know about is that it can also affect physical pain.

Our research analysed data from a large, nationally representative survey from the global analytics firm Gallup, which recorded daily measures of pain from more than two million US residents. We found that as temperatures increased so did the likelihood of people reporting they were experiencing some type of generalised physical pain.

The largest increases occurred on very hot days – around 32°C or above. Middle-aged adults and people from lower socioeconomic backgrounds were most likely to report experiencing pain on very hot days.

Why heat worsens pain

Scientists have identified several possible explanations for why you’re more likely to experience worse pain on hot days.

Some of these causes are direct triggers of pain – including dehydration caused by the heat, inflammation and other physiological processes, such as blood pressure changes which can make existing pain worse.

Other causes are indirect triggers. For instance, hot weather can increase stress, disrupt sleep, reduce wellbeing and limit our ability to perform our usual daily activities, such as exercise. All of these factors are known to amplify experiences of pain.

The relationship between pain and these potential triggers can go both ways as well. Sleep is a good example of this.

Poor sleep makes people more sensitive to pain, while pain itself makes it harder to sleep. During heatwaves, many people struggle to get a good night’s sleep, creating a vicious cycle in which poor sleep increases pain and pain further disrupts sleep. Over time, this cycle can take a toll on people’s wellbeing and quality of life.

The effects of pain extend beyond physical discomfort, as well. Pain competes for our brain’s attention. When the body hurts, attention is diverted towards coping with that pain, leaving fewer resources available for concentration, memory and decision-making. This can affect performance at work, learning in school and even everyday decision-making.

In some situations heat can be beneficial for pain – for example, applying a heating pad to help relieve lower back pain after a long day on your feet. But there’s an important difference between using targeted heat to treat a specific area of the body and being exposed to sustained high temperatures that affect the entire body. The latter places stress on multiple physiological systems and can worsen, rather than relieve, physical pain.

The consequences of heat’s effects on pain are not only personal – they’re also economic.

In our study, we estimate that hotter temperatures already cost the United States’ economy around US$2 billion (£1.5bn) every year through higher levels of pain. If temperatures continue to rise and no action is taken to help people adapt to extreme heat, these costs could exceed US$9 billion annually by 2050.

The increasingly frequent and intense heatwaves experienced in recent UK summers suggest that comparable losses in healthcare costs, reduced productivity and diminished quality of life could become an important challenge if hot summers become the new normal.

Bodily pain should therefore be recognised as another hidden health consequence of extreme heat.

Heat affects us in more ways than we often realise. The good news is that there are practical steps we can take to reduce these effects. Staying well hydrated, avoiding strenuous activity during the hottest hours of the day, seeking cool indoor spaces and planning outdoor activities for the morning or evening can all help reduce heat-related pain and discomfort.