1. Heatstroke is fatal

Signs of a heat-related illness in an individual often begin with heat exhaustion. If left untreated, this might progress to heatstroke, which is when your core body temperature is 40.6C or higher. Unfortunately, progression to death after heatstroke can happen rapidly within a few hours, even with prompt medical care.

In many situations, heat exposure is not confirmed as the underlying cause of death, so heat-related illness is massively underreported. Heat exposure can exacerbate pre-existing health conditions and in high income countries, most heat-related deaths are likely to occur from cardiovascular or respiratory diseases.

- Shak

2. The human body has a delicate natural cooling system

Coping with hot weather is dependent on the body's ability to act as a natural cooling system and humans maintain an internal temperature within a narrow range around 37C. This is independent of temperature fluctuations externally.

Sweat production is the primary physiological way to lose heat during hot weather and is needed to keep us cool. This mechanism can be diminished or delayed in susceptible groups, such as elderly people, those with chronic illnesses, or people taking certain medications.

- Shak

3. Heat can cause premature labour and low birth weight

When temperatures are high, the body sweats and blood is diverted to the skin to cool us down. This can increase the risk of dehydration, which may reduce blood flow to the placenta and result in a stressful situation for the fetus. Exposure to heat through a heat wave or a heat event, from up to one day to four weeks before birth, is known to increase the risk of premature labour. Heat exposure throughout pregnancy can also reduce the birth weight of the baby.

There is some evidence that proteins called, heat shock proteins, may play a role in the early onset of labour, but there is still much we don’t know about the exact mechanisms. Animal studies, in particular studies in sheep, show that heat stress in the third trimester alone can cause the fetus to appear stunted, similar to what you would see in a malnourished setting.

- Ana 

4. Acclimitising to hot weather does not protect our core temperatures from rising dangerously

It’s true, humans can adapt to hotter temperatures through what’s known as heat acclimitisation. Women in the Gambia will be better adapted to a hotter environment than those living in the UK, for example. But core temperatures can still elevate dangerously high because our heat exposure comes from both external and internal heat. For example, if you are in a very hot environment and working hard, a large amount of internal heat will be generated. With high external temperatures (of 40C for example), the internal heat will be unable to escape and a person will then develop heat strain.

We know from athletes, the military and other groups exposed to heat stress environments frequently, that you can force yourself to become acclimatised by having repeated episodes of getting very hot. This is why you have more deaths at the beginning of the summer than at the end of the summer - at the beginning of the summer, nobody is heat acclimatised.

- Ana

5. Reducing heat-stress is one of many benefits we will see from a zero-carbon society

When talking about reducing heat-stress and rising temperatures, it’s really useful to think about the idea of co-benefits - actions that benefit both the ecosystem and human health. We want to turn the tap off on our carbon dioxide emissions so that global heating is prevented from getting any worse.

Thinking in terms of co-benefits also means we can link together health problems and find better solutions. For example, women in The Gambia are not only working as subsistence farmers, but they are also often going to fetch water and firewood. All of these actions require a lot of energy and exposure to heat. Reducing the amount of firewood that's needed to cook (by using biogas/solar cookers etc), will help protect trees from being cut down. This will give benefits for the ecosystem and the soil structure and will provide more shade to alleviate heat and reduced heat exposure.

- Ana

Dr Shakoor Hajat

Dr Ana Bonell

Listen to the full LSHTM Viral episode, ‘What if we can’t handle the heat’.